The main objective of intraoperative neuromonitoring is to prevent new neurologic impairment by identifying it sufficiently early to allow prompt correction of its cause.
An evoked potential is a measurement of electrical activity. A waveform is recorded from the response of an electrified pattern of stimulus of nervous tissue, sensory or motor system which the subsequent recorded response pattern following the cycle of activation is analyzed.
Intraoperative monitoring uses evoked potential techniques in addition to passive real-time modalities to create a comprehensive understanding of the integrity of the nervous system in real-time while monitoring the depth of anesthesia on board a patient. The available modalities that are monitored during surgery are:
Electroencephalography (EEG), electromyography (EMG), triggered electromyography (tEMG/eSTIM), somatosensory evoked potentials (SEP), trans-cranial motor evoked potentials (tcMEP), brainstem auditory evoked potentials (BAEP), visual evoked potentials (VEP) and direct cortical motor evoked potentials (dcMEP).
One may consider two types of surgical procedures, brain and spine surgeries, that use these modalities in addition to specialized tests in various combinations for effective protection of the nervous system.
Goal is to make surgery safer for everyone, a triad relationship between the neurophysiologist, attending surgeon/resident and attending anesthesiologist/resident for the benefit of the patient. This is accomplished by detecting changes in function, identifying neuroanatomical structures that may not be visible thereby identifying areas of pathology and also potentially determining when the goal of surgery has been achieved. This is accomplished by taking advantage of the properties of the nervous system connection to muscles and the fibers and tracts that bind them.
Injuries can be detected before they become permanent and if the cause of injury is known a determination of what happened during surgical manipulation that caused the change in function. The real-time monitoring provided by the surgical neurophysiologist can make this determination by following every step of the surgery, documenting and observing any kind of deviation from baseline and relaying it to the surgeon. The surgeon and anesthesiologist must react to the neurophysiologist recommendation whom places a lot of trust in their determination. This course is to give the neurophysiologist the best chance at earning the trust of the surgeon and anesthesiologist you work for.
The neurophysiologist provides warning of risk of injury that may lead to permanent neurologic damage for the patient. We gain a REDUCED risk of postoperative and potentially improve the outcome, we can reduce the stress on the surgeon and surgical team by providing information that would otherwise be unknown (Phiroz, "I'm so glad that you are here!" Anesthesia, "Is the patient too light/too deep, What are the baseline results, is the positioning okay? Are they getting light? Was there a change there, which branch of the facial nerve do you identify, is that motor cortex or sensory cortex? I see improvements!) and can also reduce operating time by be able to provide critical information at critical moments. The immediate benefits are for the patient, by reducing postoperative neurologic deficits and less risk of loss of quality of life like walking or being able to talk. Fewer expensive complications.
Tell me more about monitoring:
Tumors can distort anatomy
What can be monitored?
Neural conduction
Neural conduction in nerves and fiber tracts changes BEFORE permanent injury occurs, there is a time period where manipulations that has caused a temporary injury, these manipulations can be reversed and no permanent injury will occur. THIS IS THE BASIS for neuromonitoring.
Synaptic Activity
Synaptic activity decreases before cell integrity is at risk, even synaptic activity can cease to occur and the cells can be revived and no permanent damage occurs. means evoked potentials change before neurological deficit occurs.
Intraoperative monitoring uses evoked potential techniques in addition to passive real-time modalities to create a comprehensive understanding of the integrity of the nervous system in real-time while monitoring the depth of anesthesia on board a patient. The available modalities that are monitored during surgery are:
Electroencephalography (EEG), electromyography (EMG), triggered electromyography (tEMG/eSTIM), somatosensory evoked potentials (SEP), trans-cranial motor evoked potentials (tcMEP), brainstem auditory evoked potentials (BAEP), visual evoked potentials (VEP) and direct cortical motor evoked potentials (dcMEP).
One may consider two types of surgical procedures, brain and spine surgeries, that use these modalities in addition to specialized tests in various combinations for effective protection of the nervous system.
Goal is to make surgery safer for everyone, a triad relationship between the neurophysiologist, attending surgeon/resident and attending anesthesiologist/resident for the benefit of the patient. This is accomplished by detecting changes in function, identifying neuroanatomical structures that may not be visible thereby identifying areas of pathology and also potentially determining when the goal of surgery has been achieved. This is accomplished by taking advantage of the properties of the nervous system connection to muscles and the fibers and tracts that bind them.
Injuries can be detected before they become permanent and if the cause of injury is known a determination of what happened during surgical manipulation that caused the change in function. The real-time monitoring provided by the surgical neurophysiologist can make this determination by following every step of the surgery, documenting and observing any kind of deviation from baseline and relaying it to the surgeon. The surgeon and anesthesiologist must react to the neurophysiologist recommendation whom places a lot of trust in their determination. This course is to give the neurophysiologist the best chance at earning the trust of the surgeon and anesthesiologist you work for.
The neurophysiologist provides warning of risk of injury that may lead to permanent neurologic damage for the patient. We gain a REDUCED risk of postoperative and potentially improve the outcome, we can reduce the stress on the surgeon and surgical team by providing information that would otherwise be unknown (Phiroz, "I'm so glad that you are here!" Anesthesia, "Is the patient too light/too deep, What are the baseline results, is the positioning okay? Are they getting light? Was there a change there, which branch of the facial nerve do you identify, is that motor cortex or sensory cortex? I see improvements!) and can also reduce operating time by be able to provide critical information at critical moments. The immediate benefits are for the patient, by reducing postoperative neurologic deficits and less risk of loss of quality of life like walking or being able to talk. Fewer expensive complications.
Tell me more about monitoring:
Tumors can distort anatomy
What can be monitored?
Neural conduction
Neural conduction in nerves and fiber tracts changes BEFORE permanent injury occurs, there is a time period where manipulations that has caused a temporary injury, these manipulations can be reversed and no permanent injury will occur. THIS IS THE BASIS for neuromonitoring.
Synaptic Activity
Synaptic activity decreases before cell integrity is at risk, even synaptic activity can cease to occur and the cells can be revived and no permanent damage occurs. means evoked potentials change before neurological deficit occurs.
EMGElectromyography is passive electrical measurements of real-time activity from the neuromuscular junction.
tEMG/eSTIMTriggered electromyography incorporates an evoked stimulus at nervous tissue and records a response from at a desired muscle/muscle group.
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Aage Moller Notes
tumors can distort anatomy, and anatomy can be revealed by electrophysiologic recrodings.
the hospital benefits by shortening the operating room time, fewer complications which are extremely expensive, if paralysis or hemipersis need various aids and treatments and risk of law suits.
long term benefits
better operating methods, revealed ways of improving operations so that the risk of injury to the nervous system decreases
better teaching of residents who figure out what they should and shouldn't do in a procedure
contributes in general to the activities of the operating room, is better to have another set of eyes to make obserations, you are a team player and can catch things that nobody else meant
also increases the awareness and understanding of the pathophysiology and normal physiology through research, for example dbs in the basal ganglia
which operations should be monitored?
must be based on risk assessment and the likelihood of an occurrence of a permanent deficit
can lose hearing versus tinnitus for example
cost/benefit ratio is economically feasible in regard to quality of medical treatment but also economically
what are the requirements?
solid knowledge of anatomy and physiology of the nervous system
skill in interpretation of neuroelectric recordings
practical skill and experience of monitoring; knowing the surgery, what the steps are during the operation and what is going to be done
good judgement is important, what to tell the surgeon, how often to tell the surgeon, how to react to an unexpected change
communications with surgeons
different surgeons have different uses of monitoring; the experienced surgeon may use monitoring less than less experienced surgeon who may need guidance or causes changes that a more experienced surgeon will not.
monitoring is not a set of warnings of eminent disasters, it provides the surgeon information with options, wait and see if it develops or if change incrases or decreases, can elect to reverse manipulation immediately so he or she does not need to worry about it in the future.
goal to avoid complications has been accomplished, we cannot avoid complications but we can reduce the risk considerably and it is also important for the neurophysiologist to visit the patient before and let them know what they are going to do and what the purpose is, to reduce risk of complications as much as possible.
Lesson 2 Anatomy and Physiology Overview
basis for understanding how changes can occur when the central nervous system is involved
conventions for anatomical directions and orientations, important to know; posterior, rostral, dorsal, caudal, etcetera* this would be a great first place to start, some surgeons use posterior and anterior where someone else would use dorsal and ventral
coronal plane used the most, most mri's and ct's are done in this scan,
focus on the middle cerebral artery, important to know what areas these are supplying with blood, incoming vessels are two carotid and vertebral arteries which feeds into the circle of willis, if
skull based tumors are important, important to know where they come out from circle of willis, middle cerebral artery is very important and supplies to brain with blood, they are numbered, M1, M2, M3 branches if they are for instance operating on aneurysms. middle cerebral artery and anterior cerebral artery and posterior cerebral artery and posterior communicating artery. these are not in the same place for everyone which is why it is importnat to have imaging, to see where these arteries are and where they supply. IOM is importatnt because it can show if a part of the brain is not functioning or anoxic with blood supply and shows if clamping could have effect by not having any collateral supply, if not if clip here can tell. IOM is the way of finding that out, there is no other way.
cerebral cortex has areas of motor control and sensory
primary visual cortex, motor control and somatosensory cortex, primary and secondary sensory cortex hidden in deep fissure is audotory cortex in temporal lobe and also areas for speech control, the frontal part of the brain is for high central nervous system functioning, planning, personallity, etcetera.
central sulcus separates primary motor area which delivers commands to muscles and sensory area and central sulcus is prominent structure that can be seen easily but many variations exist and people are different so type of monitoring for identifying the central sulcus, it looks clear in picture but if you see a brain it can look different. many surgeons would guess in parts and monitoring is very important for that.
brain in midsagitall view shows old part of the brain and the corpus callosum which connects two sides of the brain, not doing much monitoring on that area, middle of the brain there are structures like the thalamus and hypothalamus, limbic structures, see transition between the brain and spinal cord. there are a lot of tracts in these strcutrues which are targets for lots of monitoring.
floor of the fourth ventricle where monitoring is done is many different ways, can see it if cerebellum is removed, can map this area which is part of monitoring, where there are tumors, etcetera where there are tumors that need to be taken care of and to get there safely without distrubing fiber tracts and nuclei it is a good idea to have a map which can only be done electrophysiologically.
cranial nerves are monitored extensively, need to know clearly and with no doubt what the cranial nerves are doing, we have 12 pairs of symmetrical cranial nerves, important to know name and number of each of nerves because they will always refer to the numbers of the cranial nerves, IV, V, etcetera
most cranial nerves are crossed and go to the other sides of the brain, optic nerve isn't like that half of optic nerve is uncrossed, half is crossed, can tell if disorder of eye, tract or brain by the way the visual field is represented
3 motor nerves that control position of the eye and innervate extraocular muscle; there are five muscles, the 3 cranial nerve, oculomotor goes to 3 muscles and has fibers that control size of the pupil and lens for accomodation; can move the eye up and down and to the sized, can happen that this gets destroyed during surgical manipulation, renders eyes useless
i olfactory; smell
ii; optic; mediates information from the eye about what we see; can be monitored; peculiarity and differences between species; differece between rats and squirrels who are hunted, we are hunters, they have different organization of optic nerve
iii; oculomotor
iv; trochlear; superior oblique moves eyes downward toward midline; difficult to diagnose deficit of this nerve
v; trigeminal; has sensory part and motor part, sI, sII, sIII; motor part is submaxillary, buccinator, etcetera; trigeminal neuralgia is a shooting pain that attacks, can be treated by moving a blocked vessel off the trigeminal nerve or with medicine. mentalis muscle? muscle of mastication, chewing or biting enemies!
vi; abducens; lateral rectus, moves eye from midline toward the side, abducens paresis cannot move eye from midline to the side, they move their head instead
vii; facial
viii; vestibulocochlear
ix; glossopharyngeal
x;
loss of facial nerve is devastating, was frequent before for acoustic tumors or now vestibular schwannomas
nervus intermedus, there is a small nerve that runs through but it is not a nerve but a number of fascicles that runs between auditory vestibular nerve and facial nerve, almost had XIII nerves, probably involved in taste or lacrimal glands, can be associated with shooting pain that attacks can also be felt deep within the ear, patient's describe something that is very specific, deep in the ear but not in the canal and it is not there always. audiologists and laryngologists, treatment is to cut a fascicle or two of this nerve and it eliminates pain and ususally without any deficits, can be treated with medicine like with trigeminal neuralgia. medicine that is a sodium channel blocker, this is the end of chapter 2 anatomy and physiology, this is the basis of the understanding of how changes can occur during operations.
Part 3
Brainstem anatomy with specific nuclei locations, reticular nucleus, ascending pathway towards thalamus, all adjacent to the cerebellum and near medulla and midbrain, etcetera
apinal cord is housed within vertebra, 31 pairs, cervical enlargement and lumbar enlargement, spinal nerves exit laterally and anteriorly and posteriorly, sensory, motor, the roots, dorsal, ventral, etcetera, within, in the middle is grey matter, cells, white matter on the outside which are fiber tracts, grey matter has complex functions, dorsal horns are concerned with sensory function and pain and ventral part is mainly concerned with motor function, motor and sensory are separate in the spinal cord.
dorsal columns, etcetera
blood supply to the spinal cord, mainly two sources, anterior spinal artery and posterior spinal artery, segmental arteries
dorsal and ventral portions of the spinal cord have mostly different blood supplies
there is a large degree of variability, mainly posterior spinal artery supplies dorsal part of spinal cord, spinal cord itself can become compromised during surgery of course in addition to blood supply. there are a number of feeder arteries that varies within individuals
dorsal roots with nerves showing descending tracts and the anterolateral funiculus for ascending tracts for pain, not always in the place for the slide that he shows, they are on the opposite side near the motor portion and provides sensation of pain, basically showing a difference between proprioceptive and motor function.
Brainstem anatomy with specific nuclei locations, reticular nucleus, ascending pathway towards thalamus, all adjacent to the cerebellum and near medulla and midbrain, etcetera
apinal cord is housed within vertebra, 31 pairs, cervical enlargement and lumbar enlargement, spinal nerves exit laterally and anteriorly and posteriorly, sensory, motor, the roots, dorsal, ventral, etcetera, within, in the middle is grey matter, cells, white matter on the outside which are fiber tracts, grey matter has complex functions, dorsal horns are concerned with sensory function and pain and ventral part is mainly concerned with motor function, motor and sensory are separate in the spinal cord.
dorsal columns, etcetera
blood supply to the spinal cord, mainly two sources, anterior spinal artery and posterior spinal artery, segmental arteries
dorsal and ventral portions of the spinal cord have mostly different blood supplies
there is a large degree of variability, mainly posterior spinal artery supplies dorsal part of spinal cord, spinal cord itself can become compromised during surgery of course in addition to blood supply. there are a number of feeder arteries that varies within individuals
dorsal roots with nerves showing descending tracts and the anterolateral funiculus for ascending tracts for pain, not always in the place for the slide that he shows, they are on the opposite side near the motor portion and provides sensation of pain, basically showing a difference between proprioceptive and motor function.
pRT 4 Sensory potentials
shows how a stimulus affects nerve in the peripheral nervous system and how a threshold of action potentials that is conducted along an axon reaches the CNS and facilitates transmiter release, the chemical transition from the sensory cell to the sensory neuron.
muscle spindle with trigger one and myelinated axons nodes of ranvier with a sensory neuron cell body to a synaptic terminal
typical properties of mechano receptors, have fast and slow adaptation, meissner, merkel, ruffini, pacinian
shows receptive field of a dorsal column nuclus cell; shows ulnar nerve stimulation site.
inhibitory receptive fields, have inhibigory influence that will counteract the activity of the fibers that are excitatory, form of processing that is common throughout the nervous system, divergence is not very common but convergence is very common
pictures of a nerve cell which is a circle with synapses that are coming in that terminate on dendrites, branches
electrical activity of nerve cells
receptor potentials are small 0.1-10 mV duration is brief 5 - 100 ms
synaptic potentials are also small but brief to long 5 ms to 20 min and propagated active signals, such as action potentials are large 70 - 110 mV and 1-10ms in duration
the conduction velocity of nerve fibers is proportional to their diameter, these are alpha, beta, gamma and c
different types of nerve fieers carry different types of pain, here are many different fiber types and different diameters and conduction velocities and functions
most nerves are mixed nerves, containing nerve fibers with different diameters, you have to stimulate one end of the nerve and record from the other end of the nerve and you find out that potentials will arrive at different times,
shows how a stimulus affects nerve in the peripheral nervous system and how a threshold of action potentials that is conducted along an axon reaches the CNS and facilitates transmiter release, the chemical transition from the sensory cell to the sensory neuron.
muscle spindle with trigger one and myelinated axons nodes of ranvier with a sensory neuron cell body to a synaptic terminal
typical properties of mechano receptors, have fast and slow adaptation, meissner, merkel, ruffini, pacinian
shows receptive field of a dorsal column nuclus cell; shows ulnar nerve stimulation site.
inhibitory receptive fields, have inhibigory influence that will counteract the activity of the fibers that are excitatory, form of processing that is common throughout the nervous system, divergence is not very common but convergence is very common
pictures of a nerve cell which is a circle with synapses that are coming in that terminate on dendrites, branches
electrical activity of nerve cells
receptor potentials are small 0.1-10 mV duration is brief 5 - 100 ms
synaptic potentials are also small but brief to long 5 ms to 20 min and propagated active signals, such as action potentials are large 70 - 110 mV and 1-10ms in duration
the conduction velocity of nerve fibers is proportional to their diameter, these are alpha, beta, gamma and c
different types of nerve fieers carry different types of pain, here are many different fiber types and different diameters and conduction velocities and functions
most nerves are mixed nerves, containing nerve fibers with different diameters, you have to stimulate one end of the nerve and record from the other end of the nerve and you find out that potentials will arrive at different times,
PART 5 ASCENDING SENSORY PATHWAYS
classical and no-classical pathways shows the basic components from receptor to nucleus to decusssation to thalamus, etcetera and then possibly to the limbic system and association cortices
the thalamus is the gateway to the cerebral sensory cortices
the thalamus has two main parts
the ventral part is connect toprimary sensory cortices
the dorsal and medial part bypass primary sensory corrices connect to secondary ansd association corices and from subcortical connections o other parts of the brain such as to the emotional brain (amygdala nuclei)
classical pathways use the ventral part of the thalamus
the primary sensory cortices are the common final pathway for sensory information to higher brain centers
organization of the cerebral cortex is extremely complex which shows
neocortex has six layers
layer 1 the molecular layer is composed mostly of glial cells and axons raveling laterally and presumbably connect local cortical areas. it contains few cell bodies. nonspecific input from the thalamus reach neurons in layer 1
layer 2 the external granular layer is a receiving area hat sens=ds connections to other cortical areas on the same side
input from the thalamus mainly goes to layer 4 but also to other areas, this is the main input to the cortex is in layer 4, the output of the cortex. we may be stimulating cortex and remember that such stimulation can activate the thalamus and recently such stimulation has been used to treat tinnitus, possible that acting on activating the thalamus it is important to use monitoring for placement of such devices
the cerebral cortex is organized in columns, i has a lot of internal circuitry that can process information. perpendicular to the surface it will meet cells of the same kind, same kinds of cells in the same columns
two main pathways to the emotional brain, the high route and low route
the high route uses the classical pathways from thalamus to cortex and the low route goes through the thalamus and amygdala
classical and no-classical pathways shows the basic components from receptor to nucleus to decusssation to thalamus, etcetera and then possibly to the limbic system and association cortices
the thalamus is the gateway to the cerebral sensory cortices
the thalamus has two main parts
the ventral part is connect toprimary sensory cortices
the dorsal and medial part bypass primary sensory corrices connect to secondary ansd association corices and from subcortical connections o other parts of the brain such as to the emotional brain (amygdala nuclei)
classical pathways use the ventral part of the thalamus
the primary sensory cortices are the common final pathway for sensory information to higher brain centers
organization of the cerebral cortex is extremely complex which shows
neocortex has six layers
layer 1 the molecular layer is composed mostly of glial cells and axons raveling laterally and presumbably connect local cortical areas. it contains few cell bodies. nonspecific input from the thalamus reach neurons in layer 1
layer 2 the external granular layer is a receiving area hat sens=ds connections to other cortical areas on the same side
input from the thalamus mainly goes to layer 4 but also to other areas, this is the main input to the cortex is in layer 4, the output of the cortex. we may be stimulating cortex and remember that such stimulation can activate the thalamus and recently such stimulation has been used to treat tinnitus, possible that acting on activating the thalamus it is important to use monitoring for placement of such devices
the cerebral cortex is organized in columns, i has a lot of internal circuitry that can process information. perpendicular to the surface it will meet cells of the same kind, same kinds of cells in the same columns
two main pathways to the emotional brain, the high route and low route
the high route uses the classical pathways from thalamus to cortex and the low route goes through the thalamus and amygdala
Part 6
Motor pathways, anatomy of motor system descending from motor cortex through the internal capsule to respective cranial nerve nucleai or the lateral corticospinal tract, remember there is a decussation of pyramids to the spinal cord which is the final processor of motor commands.
lateral descending system
corticospinal tract connet directly to alpha motoneurons or through propriospinal interneurons
rubrospinal tract, from nucleus ruber to propriospinal interneurons
projections from sensory and motor cortices to spinal cord, motor cortex fibers mainly innervate cells in ventral part of spinal horns, whereas the cells in the somatosensory cortex innervate dorsal horns
Motor pathways, anatomy of motor system descending from motor cortex through the internal capsule to respective cranial nerve nucleai or the lateral corticospinal tract, remember there is a decussation of pyramids to the spinal cord which is the final processor of motor commands.
lateral descending system
corticospinal tract connet directly to alpha motoneurons or through propriospinal interneurons
rubrospinal tract, from nucleus ruber to propriospinal interneurons
projections from sensory and motor cortices to spinal cord, motor cortex fibers mainly innervate cells in ventral part of spinal horns, whereas the cells in the somatosensory cortex innervate dorsal horns
Lesson 3 Near and Far Field Generators
Generation of nearfield evoked potentials
compound action potentials from nerves, nuclei and fiber tracts
monopolar records activity that is propagated within the nerve and also record potentials that are conducted passivelly to that location
all amplifiers are differential amplifiers, have two inputs and differnce that inputs generate the output, we want to record with one single electode means another is a neutral positoin
always show positive as a downward projection, negative goes up
monopolar recordings yields a triphasic compound action potential
see triphasic potentials when stimulate auditory nerve, when stimulate cochlear nucleus, it is not nerve activity, monopolar will record everything from the nerve, not only what is propagated but also what is conducted because nerve is a good conductor
the waveform of the recorded potentials depends on the location of the recording
peripheral nerves approx 50 meters per second or 5 cm/msec, spinal decending tracts approx 70 to 100 m/sec, cranial nerves vary but auditory nerve is 20 m/sec
essentially three different types of pathologies
neurapraxia - most mild form of injury, prevents nerve impulses to be conducted but usually recovers all by itself
axonotmesis - more severe means that the axons are inturrupted
neurotmesis - the most severe form of nerve injury, means that the structure around the axons is also injured
nuclei can also be injured which results in different kind of discharge pattern/altered
compound action potentials from nerves, nuclei and fiber tracts
monopolar records activity that is propagated within the nerve and also record potentials that are conducted passivelly to that location
all amplifiers are differential amplifiers, have two inputs and differnce that inputs generate the output, we want to record with one single electode means another is a neutral positoin
always show positive as a downward projection, negative goes up
monopolar recordings yields a triphasic compound action potential
see triphasic potentials when stimulate auditory nerve, when stimulate cochlear nucleus, it is not nerve activity, monopolar will record everything from the nerve, not only what is propagated but also what is conducted because nerve is a good conductor
the waveform of the recorded potentials depends on the location of the recording
peripheral nerves approx 50 meters per second or 5 cm/msec, spinal decending tracts approx 70 to 100 m/sec, cranial nerves vary but auditory nerve is 20 m/sec
essentially three different types of pathologies
neurapraxia - most mild form of injury, prevents nerve impulses to be conducted but usually recovers all by itself
axonotmesis - more severe means that the axons are inturrupted
neurotmesis - the most severe form of nerve injury, means that the structure around the axons is also injured
nuclei can also be injured which results in different kind of discharge pattern/altered
Lesson 3 Part 2
depolarization will see the beginning as all positive potential out of the amplifier, when the depolarization leaves the electrode then we will see a small positivity after a large negativity. if the nerve was injured, so it doesn't conduct any longer then we will only see a positive deflection, that is a very important sign of injury* if we see a positive deflection, then we know that it is severely injured. can have conduction block
Auditory shows positivity and negativity coming from the cochlear nucleus, this was injured by heat close to the nerve where it spread throughout the nerve for injury and you see a decreased positi; triphasic potential coming from proagated injury. when injured by heat from vessel coagulation and the heat is dangerous, the positivity gradually increases while negativity decreases. that means more and more nerve fibers are not conducting. postive defelection downward, negativity is an upward deflection. shows that coagulation should be done in spurts to allow cooling to happen, and it shows how neuromonitoring helps during surgeries.
what other pathologies are there for nerves? mechanical stretching can prevent nerves from being conducted.
*patients with diabetes have poor conduction of peripheral nerve and it can mean that you don't get good recordings.
what monitoring is all about, pathologies, disorders of various kinds can interupt normal recordings, may have decreased conduction
END
depolarization will see the beginning as all positive potential out of the amplifier, when the depolarization leaves the electrode then we will see a small positivity after a large negativity. if the nerve was injured, so it doesn't conduct any longer then we will only see a positive deflection, that is a very important sign of injury* if we see a positive deflection, then we know that it is severely injured. can have conduction block
Auditory shows positivity and negativity coming from the cochlear nucleus, this was injured by heat close to the nerve where it spread throughout the nerve for injury and you see a decreased positi; triphasic potential coming from proagated injury. when injured by heat from vessel coagulation and the heat is dangerous, the positivity gradually increases while negativity decreases. that means more and more nerve fibers are not conducting. postive defelection downward, negativity is an upward deflection. shows that coagulation should be done in spurts to allow cooling to happen, and it shows how neuromonitoring helps during surgeries.
what other pathologies are there for nerves? mechanical stretching can prevent nerves from being conducted.
*patients with diabetes have poor conduction of peripheral nerve and it can mean that you don't get good recordings.
what monitoring is all about, pathologies, disorders of various kinds can interupt normal recordings, may have decreased conduction
END
Chapter 3 Part 3
Electrophysiological signs are usually detectable before permanent damage occurs, this is of course very important because it is the possibility of reducing the risks. if it was not possible to detect signs before permanent injury occurs then we would have no possibilities of reversing them so the nerves would not be injured.
monopolar would reflect passive activity, for example the cochlear nucleus could passively conduct.
bipolar theoretically does not reflect passive activity but only propagated activity, if we put an amplifer between the nerve, the best way of doing that is recording a bipolar electrode comprised of two monopolar electrodes.
the auditory nerve of course some surgeries the vestibular nerve is cut and want to make sure to cut that and not the auditory nerve so you use a bipolar recording but the surgeon must have a steady hand in order to not destroy the auditory nerve.
evoked potentials from a nucleus are taken from the auditory nerve and the initial positive-negative deflection a slow potential, when recording from cochlear nucleus you can see the auditory nerve and IX and X cranial nerves, the surface of the cochlear nucleus is the floor of the lateral recess of the fourth ventricle which is a communications area and the entrance to the foraminal recess, what do you get from the cochlear nucleus that you don't get from the nerve? There is a first negativity (upward deflection) at N1 and a second at N2 probably recording from dendrites, at N1 approx 3 ms and N2 approximately 6 ms also with P1 and P2. similar thing observed in the inferior colliculus which had a negative deflection at 6 ms.
the concept of a dipole,
farfield potentials are recorded far from where they are generated, typically have a smaller amplitude than recorded directly because we are farther but can record from more than one source, placing an electrode directly on a nerve . a long nerve generates far field potentials when neural conduction stops, the electrical conductivity of the surrounding media changes, it is bent.
Electrophysiological signs are usually detectable before permanent damage occurs, this is of course very important because it is the possibility of reducing the risks. if it was not possible to detect signs before permanent injury occurs then we would have no possibilities of reversing them so the nerves would not be injured.
monopolar would reflect passive activity, for example the cochlear nucleus could passively conduct.
bipolar theoretically does not reflect passive activity but only propagated activity, if we put an amplifer between the nerve, the best way of doing that is recording a bipolar electrode comprised of two monopolar electrodes.
the auditory nerve of course some surgeries the vestibular nerve is cut and want to make sure to cut that and not the auditory nerve so you use a bipolar recording but the surgeon must have a steady hand in order to not destroy the auditory nerve.
evoked potentials from a nucleus are taken from the auditory nerve and the initial positive-negative deflection a slow potential, when recording from cochlear nucleus you can see the auditory nerve and IX and X cranial nerves, the surface of the cochlear nucleus is the floor of the lateral recess of the fourth ventricle which is a communications area and the entrance to the foraminal recess, what do you get from the cochlear nucleus that you don't get from the nerve? There is a first negativity (upward deflection) at N1 and a second at N2 probably recording from dendrites, at N1 approx 3 ms and N2 approximately 6 ms also with P1 and P2. similar thing observed in the inferior colliculus which had a negative deflection at 6 ms.
the concept of a dipole,
farfield potentials are recorded far from where they are generated, typically have a smaller amplitude than recorded directly because we are farther but can record from more than one source, placing an electrode directly on a nerve . a long nerve generates far field potentials when neural conduction stops, the electrical conductivity of the surrounding media changes, it is bent.
Lesson 4 The Auditory System
Auditory nerve is at risk in many surgeries, cerebellopontine angle, but monitoring of it can be used in other operations, when the brainstem is being manipulated. the auditory system plays an important role and it's important to undersatnd the basics of the auditory nerve and ear.
the cross section of the ear shows the tympanic membrane, the incus, the malleus and the stapes, the oval window and the auditory nerve.
the patient could have hearing problems that are totally unrelated and make it difficult to observe the function of the audiotry nerve.
the tympanic membrane, the coclea is fluid filled and contain sensory cells that turn into nerve impulses, low frequency, high frequency, the coclhear nerve and vestibular system, the balance system. the facial nerve is not directly involved in the ear of course because it controls the muslses of the face but it travels with the auditory and vestibular nerve so it can also be at risk.
the anatomical relations of these structures
basilar membrane separates the cochleas fluid filled canals and has the hair cells baby
inner hair cells and outer hair cells are along the basilar membrane and the inner hair cells are different than the outer hair cells the inner hair cells act as sensory cells as we know it in other sensory systems mediating information about sounds to the brain via the auditory nerve whereas the outer hair cells amplifiy the motion of the basilar membrane, three rows of outer hair cells and one row of inner hair cells, outer hair cells are in w formation and inner hair cells are more of a straight line. hair cells are mechanosensitive, when they are deflected in one direction the discharge rate increases and in the other direction decreases.
basilar membrane is tuned to a specific frequency travelling wave motion, sound will set up a motion along the basilar membrane which causes a wave which travels from the base toward the apex giving it frequency selectivity. activity of the hair cells generate nerve impulses in the fibers of the auditory nerve but also gives rise to a bunch of potentials in the ear and some of them have importance for neuromonitoring.
cochlear microphonics, summating potentails and compound action potentials. the summating potentials and cochlear microphonics are generated by the hair cells and we can visualize all three kinds by selecting the sound of which we stimulate the ear.
ascending auditory pathway shows the cochlea first arrives at the cochlear nucleus crosses over to the other side on the lateral lemnisucus where cells terminate on the central nucleus of the inferior colliculus to the thalamus where cells terminate in the medial geniculate body which is in the ventral part of the thalamus which then project to the primary auditory cortex = this is simplified but these are important structures.
the anatomical location shows where the cochlear nucleus is, the floor of the fourth ventricle with the cerebellum removed.
the cross section of the ear shows the tympanic membrane, the incus, the malleus and the stapes, the oval window and the auditory nerve.
the patient could have hearing problems that are totally unrelated and make it difficult to observe the function of the audiotry nerve.
the tympanic membrane, the coclea is fluid filled and contain sensory cells that turn into nerve impulses, low frequency, high frequency, the coclhear nerve and vestibular system, the balance system. the facial nerve is not directly involved in the ear of course because it controls the muslses of the face but it travels with the auditory and vestibular nerve so it can also be at risk.
the anatomical relations of these structures
basilar membrane separates the cochleas fluid filled canals and has the hair cells baby
inner hair cells and outer hair cells are along the basilar membrane and the inner hair cells are different than the outer hair cells the inner hair cells act as sensory cells as we know it in other sensory systems mediating information about sounds to the brain via the auditory nerve whereas the outer hair cells amplifiy the motion of the basilar membrane, three rows of outer hair cells and one row of inner hair cells, outer hair cells are in w formation and inner hair cells are more of a straight line. hair cells are mechanosensitive, when they are deflected in one direction the discharge rate increases and in the other direction decreases.
basilar membrane is tuned to a specific frequency travelling wave motion, sound will set up a motion along the basilar membrane which causes a wave which travels from the base toward the apex giving it frequency selectivity. activity of the hair cells generate nerve impulses in the fibers of the auditory nerve but also gives rise to a bunch of potentials in the ear and some of them have importance for neuromonitoring.
cochlear microphonics, summating potentails and compound action potentials. the summating potentials and cochlear microphonics are generated by the hair cells and we can visualize all three kinds by selecting the sound of which we stimulate the ear.
ascending auditory pathway shows the cochlea first arrives at the cochlear nucleus crosses over to the other side on the lateral lemnisucus where cells terminate on the central nucleus of the inferior colliculus to the thalamus where cells terminate in the medial geniculate body which is in the ventral part of the thalamus which then project to the primary auditory cortex = this is simplified but these are important structures.
the anatomical location shows where the cochlear nucleus is, the floor of the fourth ventricle with the cerebellum removed.
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takes time for impulses to get from one place to another
The Auditory Nerve is approximately 2.5cm at 20m/s conduction velocity means it would take 1 or 1.2 ms to get from ear to cochlear nucleus, the same for the lengths of the lateral lemniscus and so forth,
record from auditory nerve in operations of the posterior fossa, trigeminal neuraligia, tinnitus, hemi-facial spasm, all of these risk the auditory nerve, important to monitor auditory nerve.
we can record far field potentisla by putting electrodes on scalp, vertex, and ear
using signal averaging, adding stimuli together, such as click stimuli and adding the potentials, the reason is the background potentials are not related to the stimulus but appear randomly and the structures are closely associated and therefore will add up and the more the clearer they will be in the final record. of course there is noise interference. these two factors, signal averaging make it possible to obtain these abr, auditory brain responses in the operating room.
what is it that we look at?
we look at the latencies, any injury of the nerve will cause it to conduct more slowly, the latencies of structures will decrease, we want to determine the latency of these peaks and enhance them, we also want to know where theses peaks come from, peak one is generated by the distal part of the auditory nerve, peak 2 is central auditory nerve peak 3 is mainly cochlear nucleus, peak 4 unknown, probably generatied by structures by midline, peak 5 is generated by the termination of the lateral lemniscus in the contralatera inferior colliculus. the nerves or fiber tracts tend to
*there was a whole mess of stuff that was here but when i went to publish, weebly locked me out...l
The Auditory Nerve is approximately 2.5cm at 20m/s conduction velocity means it would take 1 or 1.2 ms to get from ear to cochlear nucleus, the same for the lengths of the lateral lemniscus and so forth,
record from auditory nerve in operations of the posterior fossa, trigeminal neuraligia, tinnitus, hemi-facial spasm, all of these risk the auditory nerve, important to monitor auditory nerve.
we can record far field potentisla by putting electrodes on scalp, vertex, and ear
using signal averaging, adding stimuli together, such as click stimuli and adding the potentials, the reason is the background potentials are not related to the stimulus but appear randomly and the structures are closely associated and therefore will add up and the more the clearer they will be in the final record. of course there is noise interference. these two factors, signal averaging make it possible to obtain these abr, auditory brain responses in the operating room.
what is it that we look at?
we look at the latencies, any injury of the nerve will cause it to conduct more slowly, the latencies of structures will decrease, we want to determine the latency of these peaks and enhance them, we also want to know where theses peaks come from, peak one is generated by the distal part of the auditory nerve, peak 2 is central auditory nerve peak 3 is mainly cochlear nucleus, peak 4 unknown, probably generatied by structures by midline, peak 5 is generated by the termination of the lateral lemniscus in the contralatera inferior colliculus. the nerves or fiber tracts tend to
*there was a whole mess of stuff that was here but when i went to publish, weebly locked me out...l
digitial filtering can use different filters for he same record at the same time and you can take the one that you think is the most suitable
filtering can elimnate slow potentials, the N10 potential
optimal electrode placement chapter four mastoid to vertex or mastoid to forehead are not good, the earlobe is good
the dipoles of peak 1 2 and 3 are horizontal from one earlobe to another, in order to use these peaks in the best way, one on one earlobe and the other on the other earlobe, there is no equivalent of a dipole in the head that is just a description. the dipole for peak 5 are perpendicular to these dipoles (the first three peaks) that means the earlobe is not opitmal to record peak five means that vertex and cspine? AAGE moller does a two channel ABR.
the recording is reduction of electrical interference that exists in the recording the more responses are needed to be added and the longer time it will take to determine an interpretable record.
if we want to improve the signal to noise ratio need to reduce averaging, because more trials and more waiting is not ideal, need to reduce signal to noise the square root of the number of responses that are added, compare the situation 100 responses added and we want to increase signal to noise ratio with a factor of 2 then we have to increase the responses by a factor of four, so 400 responses. but what if you have 1000 noises added and want to improve signal to noise ratio to 2 and do 4X have to go to 4000 responses!
recording directly from the auditory nerve is ideal but it needs to be exposed, you can put an electrode on it.
recording from the auditory nerve should be done with an, its inside the auditory meatus and cerebellar pontine angle, an electrode with a cotton wick is a sutiable electrode to record from it. it's. to determine which part is auditory and which part is vestibular, appropriate to review the anatomy as you see it in the cerebellar pontine angle.
filtering can elimnate slow potentials, the N10 potential
optimal electrode placement chapter four mastoid to vertex or mastoid to forehead are not good, the earlobe is good
the dipoles of peak 1 2 and 3 are horizontal from one earlobe to another, in order to use these peaks in the best way, one on one earlobe and the other on the other earlobe, there is no equivalent of a dipole in the head that is just a description. the dipole for peak 5 are perpendicular to these dipoles (the first three peaks) that means the earlobe is not opitmal to record peak five means that vertex and cspine? AAGE moller does a two channel ABR.
the recording is reduction of electrical interference that exists in the recording the more responses are needed to be added and the longer time it will take to determine an interpretable record.
if we want to improve the signal to noise ratio need to reduce averaging, because more trials and more waiting is not ideal, need to reduce signal to noise the square root of the number of responses that are added, compare the situation 100 responses added and we want to increase signal to noise ratio with a factor of 2 then we have to increase the responses by a factor of four, so 400 responses. but what if you have 1000 noises added and want to improve signal to noise ratio to 2 and do 4X have to go to 4000 responses!
recording directly from the auditory nerve is ideal but it needs to be exposed, you can put an electrode on it.
recording from the auditory nerve should be done with an, its inside the auditory meatus and cerebellar pontine angle, an electrode with a cotton wick is a sutiable electrode to record from it. it's. to determine which part is auditory and which part is vestibular, appropriate to review the anatomy as you see it in the cerebellar pontine angle.
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the recorded potentials from the nerve is like any recording from a monopolar electrode, a triphasic waveform
condensation and rarefaction, people with hearing loss have a difference if you look at both forms,
better to record condensation and rarefaction separately not together
MOLLER PART 4
even a slight injury can have an effect, we have potentials not hearing, we get information about their hearing afterwards after they can make an audiological assessment. audiogram and speech siscrimination, tinnitus devastating no intellectual work
even a slight injury can have an effect, we have potentials not hearing, we get information about their hearing afterwards after they can make an audiological assessment. audiogram and speech siscrimination, tinnitus devastating no intellectual work
Moller part 5
continuation of chapter 4, the practical aspects of recording in the operating room
practical way of displaying ABR for intraoperative monitoring in an operation for a vestibular schwannoma
vertex positivity is displayed downwards, also need to verify that the artery that supplies the cochlea is not manipulated or removed during tumor removal
a nucleus generates large far field potentials when dendrites are arranged orderly and
injuries to the auditory nerve may happen after closure of dura
continuation of chapter 4, the practical aspects of recording in the operating room
practical way of displaying ABR for intraoperative monitoring in an operation for a vestibular schwannoma
vertex positivity is displayed downwards, also need to verify that the artery that supplies the cochlea is not manipulated or removed during tumor removal
a nucleus generates large far field potentials when dendrites are arranged orderly and
injuries to the auditory nerve may happen after closure of dura
The Somatosensory System
dorsal column - fine touch, inturrupted in dorsal column nuceli
anteriolateral, pain temperature and deep touch, inturrupted in dorsal horn of spinal cord and crosses at segmental level and travels up the spinal cord on the opposite side
the organization of the spinal cord
organization of the dorsal and ventral horn of the spinal cord
anteriolateral, pain temperature and deep touch, inturrupted in dorsal horn of spinal cord and crosses at segmental level and travels up the spinal cord on the opposite side
the organization of the spinal cord
organization of the dorsal and ventral horn of the spinal cord
dorsal roots innervate dorsal horn cells several segments up and down the spinal cord
Part 2
dermatomes are innervated from different segments
dermatomes are innervated from different segments
notice that C1 does not have a dorsal root
stimulation of ulnar and median nerves
somatosensory pathway through the face is mainly through the trigeminal nerve
stimulation of ulnar and median nerves
somatosensory pathway through the face is mainly through the trigeminal nerve
Part 3
main branches from the trigeminal nerve but also at C2 the second cervical vertebrae the dorsal root innervates part of the skin at the head, the rear of the head coming under the platysma and C3 is at the neck
main branches from the trigeminal nerve but also at C2 the second cervical vertebrae the dorsal root innervates part of the skin at the head, the rear of the head coming under the platysma and C3 is at the neck
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sensory parts of cranial nerve V, IX and X these fibers joins the medial lemniscus and terminate in the ventral part of the thalamus, the ventral posterior medial part of the thalamus. and synapse with cells in the rostral trigeminal nucleus and their axons cross the midline to reach the ventral thalamus (VPM)
The body surface is projected onto the surface of the somatosensory cortex, the tongue is in the most lateral part of the somatosensory cortex, the hand in the middle and the foot and leg in the middle part of the brain. this is important when want to record, for stimulation of the leg we put the electrode on the scalp for midline and for the hand we put the electrode on the side of the head in the parietal area.
The anterolateral system is involved in temperature and pain and some deep touch particularly in the belly, it is phylogenetically older than the dorsal column system and is more developed in animals than it is in humans and it is less developed in primates. it consists of three or four different fiber tracts, different ascending tracts, the spinothalamic tract, the spinomesenphalic tracts, the spinoreticular tract and the paleospinal tract.
the spinothalamic tract, the periaqueductal grey has significant participation in pain, the dorsal connections to the thalamus are thought to be the most important for pain and ascend to association cortices whereas ventral part of thalamus heads to somatosensory cortex
the spinothalamic tract and it's nuclei is mainly dor
spinoreticular is bilateral, has an uncrossed and crossed path, connects to dorsal thalamus and gives off collaterals to reticular formation
spinomesencephalic path goes from receptor to dorsal horn to periaquductal grey through hypothalamus and amygdala for emotional response to pain
descending connnections from the cerebral cortex that reach the thalamus the dorsal column nuclei and the dorsal horns
the descending pathways are mainly from the periaqueductal gray (PAG) that reach the dorsal horn in the spinal cord; now it is known that there are opiod receptors in the spinal cord
there are several types of pain; body pain can be caused by:
1. stimulation of pain receptors
2. overstimulation of mechanoreceptors
3. injury, asphyxia and inflammation to body tissues
actue pain sensation from stimulation is caused by stimulation of nociceptors or overstimulation of other receptors are of two kinds, one kind mediated by A delta fibers one kind mediated by C fibers, first pain is distinct, has a spike, and the second phase of pain is slow and burning mediated by C fibers, when use local anesthetics it is mostly affecting the C fibers, if you visit the dentist, you are mostly pain free but still have sensation, if compress the nerve it is Delta fibers that are affected and can still have pain but lose sensation.
classifications of nerve fibers
A fibers which are myelinated, A delta pain, A Beta for touch and A alpha mostly for motor control for motor fibers, C fibers are small unmyelinated fibers for slow, grinding, burning kind of pain. different kind of fibers give a different type of pain sensation.
SOMATOSENSORY EVOKED POTENTIALS
anatomy and physiology of the somatosensory system
generation of the SSEP
how pathologies can change these potentials
There are two kinds that are important for monitoring; upper limb from median or ulnar nerve and those that are elicited by stimulating from the lower limb, ususally on the foot
The waveform of the elicited responses depends on the placement of the recording electrodes,
The body surface is projected onto the surface of the somatosensory cortex, the tongue is in the most lateral part of the somatosensory cortex, the hand in the middle and the foot and leg in the middle part of the brain. this is important when want to record, for stimulation of the leg we put the electrode on the scalp for midline and for the hand we put the electrode on the side of the head in the parietal area.
The anterolateral system is involved in temperature and pain and some deep touch particularly in the belly, it is phylogenetically older than the dorsal column system and is more developed in animals than it is in humans and it is less developed in primates. it consists of three or four different fiber tracts, different ascending tracts, the spinothalamic tract, the spinomesenphalic tracts, the spinoreticular tract and the paleospinal tract.
the spinothalamic tract, the periaqueductal grey has significant participation in pain, the dorsal connections to the thalamus are thought to be the most important for pain and ascend to association cortices whereas ventral part of thalamus heads to somatosensory cortex
the spinothalamic tract and it's nuclei is mainly dor
spinoreticular is bilateral, has an uncrossed and crossed path, connects to dorsal thalamus and gives off collaterals to reticular formation
spinomesencephalic path goes from receptor to dorsal horn to periaquductal grey through hypothalamus and amygdala for emotional response to pain
descending connnections from the cerebral cortex that reach the thalamus the dorsal column nuclei and the dorsal horns
the descending pathways are mainly from the periaqueductal gray (PAG) that reach the dorsal horn in the spinal cord; now it is known that there are opiod receptors in the spinal cord
there are several types of pain; body pain can be caused by:
1. stimulation of pain receptors
2. overstimulation of mechanoreceptors
3. injury, asphyxia and inflammation to body tissues
actue pain sensation from stimulation is caused by stimulation of nociceptors or overstimulation of other receptors are of two kinds, one kind mediated by A delta fibers one kind mediated by C fibers, first pain is distinct, has a spike, and the second phase of pain is slow and burning mediated by C fibers, when use local anesthetics it is mostly affecting the C fibers, if you visit the dentist, you are mostly pain free but still have sensation, if compress the nerve it is Delta fibers that are affected and can still have pain but lose sensation.
classifications of nerve fibers
A fibers which are myelinated, A delta pain, A Beta for touch and A alpha mostly for motor control for motor fibers, C fibers are small unmyelinated fibers for slow, grinding, burning kind of pain. different kind of fibers give a different type of pain sensation.
SOMATOSENSORY EVOKED POTENTIALS
anatomy and physiology of the somatosensory system
generation of the SSEP
how pathologies can change these potentials
There are two kinds that are important for monitoring; upper limb from median or ulnar nerve and those that are elicited by stimulating from the lower limb, ususally on the foot
The waveform of the elicited responses depends on the placement of the recording electrodes,
P for positive and N for negative and a number subscript that tells the normal latency, not the actual latency of the peak. notice the difference from a noncephalic reference, meaning the other end of the amplifier is placed off the head, like on the neck or shoulder, a non-cephalic.
we see the first potential is P9 followed by P11 then a complex of P14/P18 can also see N18 at 18 ms and then there is a huge potential at N20. if we were to place electrodes differently so that we put them on the forehead we only see the N20.
P9 brachial plexus enters the spinal cord
N13 also coming from spinal cord (would get this reference from placement at C6)
P11 is in the dorsal horn and has nothing to do with transmission to the brain, not an important potential to observe when monitoring
P14/16 generated at dorsal column nuclei
P18 in midbrain/brainstem
N20 generated in primary somatosensory cortex
these can be different because peoplehave different lengths of arms and if are cool, the conduction velocity will go down so the latency will go up. the normal values of these latencies,
waveform depends on how electrodes are placed, the difference between having a noncephalic reference and one on the forehead are quite differenct. if we move electrodes to other locations we will have different waveforms. waveform of these potentials depends greatly on how electrodes are placed.
10-20 system, different positions on the scalp have a letter and a subscript, odd numbers on left, even numbers on right, the midline is letter Z as a subscript.
somatosensory at median nerve are often recorded a little behind C3 or C4 electrode, just about over somatosensory cortex
End of Chapter 5 part 3
we see the first potential is P9 followed by P11 then a complex of P14/P18 can also see N18 at 18 ms and then there is a huge potential at N20. if we were to place electrodes differently so that we put them on the forehead we only see the N20.
P9 brachial plexus enters the spinal cord
N13 also coming from spinal cord (would get this reference from placement at C6)
P11 is in the dorsal horn and has nothing to do with transmission to the brain, not an important potential to observe when monitoring
P14/16 generated at dorsal column nuclei
P18 in midbrain/brainstem
N20 generated in primary somatosensory cortex
these can be different because peoplehave different lengths of arms and if are cool, the conduction velocity will go down so the latency will go up. the normal values of these latencies,
waveform depends on how electrodes are placed, the difference between having a noncephalic reference and one on the forehead are quite differenct. if we move electrodes to other locations we will have different waveforms. waveform of these potentials depends greatly on how electrodes are placed.
10-20 system, different positions on the scalp have a letter and a subscript, odd numbers on left, even numbers on right, the midline is letter Z as a subscript.
somatosensory at median nerve are often recorded a little behind C3 or C4 electrode, just about over somatosensory cortex
End of Chapter 5 part 3
Upper limb SSEPs are used for monitoring intracranial operations from median nerve, the cortical components of the SSeP are affected by decrease in oxygenation (blood supply) the changes in SSEP in response to ischemia occur before permanent damage. see changes in SSEPs first and can reverse.
it is advantageous to use the central conduction time rather than the absolute latency times, the reason is that stimulating the medain nerve makes use of the peripheral nerve on the arm, arm is usually exposed, meaning that conduction time will affect, the operating room is cold, meaning the conduction time in the peripheral part, namely the median nerve, will slowly increase that is of course benign and should not cause any alarm to the surgeon
End of Chapter 5 part 4
it is advantageous to use the central conduction time rather than the absolute latency times, the reason is that stimulating the medain nerve makes use of the peripheral nerve on the arm, arm is usually exposed, meaning that conduction time will affect, the operating room is cold, meaning the conduction time in the peripheral part, namely the median nerve, will slowly increase that is of course benign and should not cause any alarm to the surgeon
End of Chapter 5 part 4
Chapter 5 part 5
The time the potentials from the dorsal column nuclei to the N20 as illustrated, the beginning of N20 has a central conduction time of approx 6.6ms, if look at the peak of P14 then it is about 6.1ms to N20, another advantage of using central conduction time is that the length of the arm does not affect the results.
Erbs point is just about at the clavicle and is over the brachial plexus and shows responses from here, it is practical to have this response because it shows that the stimulation was affected and activiating the peripheral nerves; it is a gauge for stimulation, makes sure that the stimulation is sufficient to activate the peripheral nerve.
remember that individuals have different responses, so if the response does not show up as it does in the textbook then it is part of individual variation.
it is possible to record ipsilateral and contralateral response from both sides that can show alternating stimulation of both sides.
In order to understand results from monitoring we need to understand the blood supply of the brain. the middle cerebral artery and anterior cerebral artery mostly occur for aneurysms here, they mostly occur at the middle cerebral artery. there are many branches and are labeled 1, 2 and 3. clipping of aneurysms can glean if responses disappear when the branch is clipped or the blood supply has disappeared. the clipping of these branches is necessary in order to repair the artery for the aneurysm. when the clip is removed because of the evoked potentials disappearance shows that they can come back and the surgeon will have to develop another strategy.
the effect of occluding the internal carotid artery
loss of potentials during carotid endarterectomy once ICA is closed, sometimes it is important to stop the blood flow to an artery while the cleaning is done, is it possible to occlude the vessel in question, if there are no changes, it is obviously safe, if it does cause changes then something should be done differently.
operation to remove a benign meningioma, when the bone was opened, trepanation, the somatosensory evoked potential disappears, big surprise because it shouldn't have caused anything to happen. what happened us that the brachial plexus and head needed repositioned. this is not uncommon, many people get damage to the brachial plexus during positioning. median nerve should be used when patients are placed in an awkward position on the operating room table. it is a good way to safeguard agains this mishap.
there are artifacts in recording of cortical SSEP in sitting position, the patient was in a sitting position, air crept in under the dura and compromised the recording electrodes on the scalp. there was no electrical connection to the cerebral cortex and subsequently the potentials disappeared. much reduced amplitude came back to almost normal when the patient was at the end of the operation was placed in a supine position.
lower limb ssep stimulating left posterior tibial nerve. frontal recording non-cephalic reference yields a much smaller recording, the middle recording from a non-cephalic reference shows more waveforms (18:00) if you take the difference between A and B. It can sometime be an advantage to take the difference because it can suppress noise.
the neural generators of the lower limb SSEP are not as clearly understood as the upper limb, but they should just go through the gracilis? cuneatus?
posterior tibial nerve that is stimulated and can record at the popliteal fossa at the knee to make sure the stimulation is accurate. responses to stimulation of the posterior tibial nerve. the waveform of lower limb SSEP depends on the placement of the recording electrodes.
location of the posterior tibial nerve is to show where the anatomy of the foot.
some other responses directly recorded from the dorsal column nuclei compared with the scalp recordings.
monitoring of the lower limb ssep is important and done very often, especially when there is a risk of damaging the spinal cord or dorsal roots.
amytal "provocative" test during embolization of a vascular spinal tumor. the problem is if ithe blood supply is compromised if the tumor is removed. to test that it is often used to temporary occlude vessels, if the process involves embolization (permanently blocking vessels that supply such a tumor) to test to see if it is possible, amytal is injected and that will inactivate neural tissue that is supplied from this tissue to the vessel. by watching the evoked potentials can see if it was important or if it can be blocked permanently.
End of Chapter 5 part 5
The time the potentials from the dorsal column nuclei to the N20 as illustrated, the beginning of N20 has a central conduction time of approx 6.6ms, if look at the peak of P14 then it is about 6.1ms to N20, another advantage of using central conduction time is that the length of the arm does not affect the results.
Erbs point is just about at the clavicle and is over the brachial plexus and shows responses from here, it is practical to have this response because it shows that the stimulation was affected and activiating the peripheral nerves; it is a gauge for stimulation, makes sure that the stimulation is sufficient to activate the peripheral nerve.
remember that individuals have different responses, so if the response does not show up as it does in the textbook then it is part of individual variation.
it is possible to record ipsilateral and contralateral response from both sides that can show alternating stimulation of both sides.
In order to understand results from monitoring we need to understand the blood supply of the brain. the middle cerebral artery and anterior cerebral artery mostly occur for aneurysms here, they mostly occur at the middle cerebral artery. there are many branches and are labeled 1, 2 and 3. clipping of aneurysms can glean if responses disappear when the branch is clipped or the blood supply has disappeared. the clipping of these branches is necessary in order to repair the artery for the aneurysm. when the clip is removed because of the evoked potentials disappearance shows that they can come back and the surgeon will have to develop another strategy.
the effect of occluding the internal carotid artery
loss of potentials during carotid endarterectomy once ICA is closed, sometimes it is important to stop the blood flow to an artery while the cleaning is done, is it possible to occlude the vessel in question, if there are no changes, it is obviously safe, if it does cause changes then something should be done differently.
operation to remove a benign meningioma, when the bone was opened, trepanation, the somatosensory evoked potential disappears, big surprise because it shouldn't have caused anything to happen. what happened us that the brachial plexus and head needed repositioned. this is not uncommon, many people get damage to the brachial plexus during positioning. median nerve should be used when patients are placed in an awkward position on the operating room table. it is a good way to safeguard agains this mishap.
there are artifacts in recording of cortical SSEP in sitting position, the patient was in a sitting position, air crept in under the dura and compromised the recording electrodes on the scalp. there was no electrical connection to the cerebral cortex and subsequently the potentials disappeared. much reduced amplitude came back to almost normal when the patient was at the end of the operation was placed in a supine position.
lower limb ssep stimulating left posterior tibial nerve. frontal recording non-cephalic reference yields a much smaller recording, the middle recording from a non-cephalic reference shows more waveforms (18:00) if you take the difference between A and B. It can sometime be an advantage to take the difference because it can suppress noise.
the neural generators of the lower limb SSEP are not as clearly understood as the upper limb, but they should just go through the gracilis? cuneatus?
posterior tibial nerve that is stimulated and can record at the popliteal fossa at the knee to make sure the stimulation is accurate. responses to stimulation of the posterior tibial nerve. the waveform of lower limb SSEP depends on the placement of the recording electrodes.
location of the posterior tibial nerve is to show where the anatomy of the foot.
some other responses directly recorded from the dorsal column nuclei compared with the scalp recordings.
monitoring of the lower limb ssep is important and done very often, especially when there is a risk of damaging the spinal cord or dorsal roots.
amytal "provocative" test during embolization of a vascular spinal tumor. the problem is if ithe blood supply is compromised if the tumor is removed. to test that it is often used to temporary occlude vessels, if the process involves embolization (permanently blocking vessels that supply such a tumor) to test to see if it is possible, amytal is injected and that will inactivate neural tissue that is supplied from this tissue to the vessel. by watching the evoked potentials can see if it was important or if it can be blocked permanently.
End of Chapter 5 part 5
Chapter 5 part 6
Neural generators of the lower limb SSEP are not as clearly understood, this is a repeat of stuff mentioned earlier.
recordings can illustrate something about the gross origin of these potentials, the posterior tibial nerve is stimulated and can record potentials at popliteal fossa to make sure stimulation is accurate. recording from over C2 with a reference in the front will reveal a potential with a latency of 34 mS, this is regarded as a subcortical potential likely in the dorsal column nuclei, if we record from Cz and a frontal reference then the main potential will occur at about 41mS, this is regarded as the potentials generated by the somatosensory cortex.
monitoring could be of less value for certrain surgeries because it is not possible to reverse the change,
comparison between dermatomal and tibial SEP, can be examined even though only one root is stimulated
anesthesia can reduce amplitude of SSEPs, principals of the same, it builds up in the fatty tissues, it is related to the concentration that the effect of the concentration is increased and almost extinguishes the response. there is a linear relationship between the concentration of inhalation agents and the latency of the potentials, the latency increases, almost anything you can think of as bad can increase the latency, stretching, heating, cooling, anesthetic, etcetera.
in summary it can be said that monitoring somatosensory evoked potentials are important, have to remember that the blood supply to the spinal cord is different for the dorsal and ventral parts, it is possible to injure the ventral part while have potentials from the ventral part, also calls for monitoring the anterior part with motor evoked potentials. but there is one way that should be mentioned regarding SSEP recorded in operations on the spine, the possibility of monitoring the ventral part, for motor evoked potentials has come much later. pioneering work done in scloliosis cases during the seventies by dr. brown, he made use of some phenomenon similar to called a spinal shock if the ventral part is injured for instance by interuppting the blood supply then some abnormality may spread to the dorsal part, normally the person would see this recovery and say that it is good but it should be taken as a warning that perhaps something has happened to the ventral part of the spinal cord. it is common that if such a suspicioun occurs then a wake up test can be useful. it may sound dramatic but it is not and could be useful.
Neural generators of the lower limb SSEP are not as clearly understood, this is a repeat of stuff mentioned earlier.
recordings can illustrate something about the gross origin of these potentials, the posterior tibial nerve is stimulated and can record potentials at popliteal fossa to make sure stimulation is accurate. recording from over C2 with a reference in the front will reveal a potential with a latency of 34 mS, this is regarded as a subcortical potential likely in the dorsal column nuclei, if we record from Cz and a frontal reference then the main potential will occur at about 41mS, this is regarded as the potentials generated by the somatosensory cortex.
monitoring could be of less value for certrain surgeries because it is not possible to reverse the change,
comparison between dermatomal and tibial SEP, can be examined even though only one root is stimulated
anesthesia can reduce amplitude of SSEPs, principals of the same, it builds up in the fatty tissues, it is related to the concentration that the effect of the concentration is increased and almost extinguishes the response. there is a linear relationship between the concentration of inhalation agents and the latency of the potentials, the latency increases, almost anything you can think of as bad can increase the latency, stretching, heating, cooling, anesthetic, etcetera.
in summary it can be said that monitoring somatosensory evoked potentials are important, have to remember that the blood supply to the spinal cord is different for the dorsal and ventral parts, it is possible to injure the ventral part while have potentials from the ventral part, also calls for monitoring the anterior part with motor evoked potentials. but there is one way that should be mentioned regarding SSEP recorded in operations on the spine, the possibility of monitoring the ventral part, for motor evoked potentials has come much later. pioneering work done in scloliosis cases during the seventies by dr. brown, he made use of some phenomenon similar to called a spinal shock if the ventral part is injured for instance by interuppting the blood supply then some abnormality may spread to the dorsal part, normally the person would see this recovery and say that it is good but it should be taken as a warning that perhaps something has happened to the ventral part of the spinal cord. it is common that if such a suspicioun occurs then a wake up test can be useful. it may sound dramatic but it is not and could be useful.
Lesson 6 The Motor System
Monitoring of Spinal Motor Systems
have similarities with sensory motor systems just turned backward. both motor and sensory systems have two parts. motor systems have lateral and medial systems.
monitoring of motor systems depends on the understanding of anatomy and physiology of the motor systems.
lateral descending system consists of the corticospinal tract and rubrospinal tract
corticospinal tract connects directly to alpha motor neurons and the final common pathway
the rubrospinal tract originates in the nucleus ruber, it is very small in humans and probably plays a minimal role in the normal funciton of the spinal motor system, it can simply be ignored but can glean into patient history, if have trouble with fine touch and discrimination, rubbing your bro
somatotopic organization of the motor cortex show a different homunculus.
primary motor cortex issues commands to muscles however it receives it's input from a wide variety of areas, Broadmans 6 lateral premotor area, supplementary motor area, primary motor area is brodmanns area 4.
Medial Descending System
Reticulospinal tract
Tectospinal Tract superior colluculus mainly sends info down to spinal cord
Vestibulospinal tract origin is vestibular nuclei
posture and walking and input from medial system, in monitoring spinal motor systems restricting only to corticospinal tracts puts one at a disadvantage, can interfere with persons ability to walk or stand up, etcetera. in the future I'm sure we will be able to monitor the medial system but now it's not done.
the distincition of pyramidal and non-pyramidal system does not have a foundation in anatomy, the basal ganglia and thalamus process information from the motor cortex and then send it back for processing, a feedback loop. this is very important because now we know that the descending pathways carry information from the motor cortex and information has been further processed information. so there is no distinction between what comes directly from the motor cortex and what has been processed by the basal ganglia. the motor cortex issues commands and the basal ganglia and thalamus process it they just command it from the cortex. these nuclei have different names of course and are organized in groups.
chapter 6 part 1 end
Monitoring of Spinal Motor Systems
have similarities with sensory motor systems just turned backward. both motor and sensory systems have two parts. motor systems have lateral and medial systems.
monitoring of motor systems depends on the understanding of anatomy and physiology of the motor systems.
lateral descending system consists of the corticospinal tract and rubrospinal tract
corticospinal tract connects directly to alpha motor neurons and the final common pathway
the rubrospinal tract originates in the nucleus ruber, it is very small in humans and probably plays a minimal role in the normal funciton of the spinal motor system, it can simply be ignored but can glean into patient history, if have trouble with fine touch and discrimination, rubbing your bro
somatotopic organization of the motor cortex show a different homunculus.
primary motor cortex issues commands to muscles however it receives it's input from a wide variety of areas, Broadmans 6 lateral premotor area, supplementary motor area, primary motor area is brodmanns area 4.
Medial Descending System
Reticulospinal tract
Tectospinal Tract superior colluculus mainly sends info down to spinal cord
Vestibulospinal tract origin is vestibular nuclei
posture and walking and input from medial system, in monitoring spinal motor systems restricting only to corticospinal tracts puts one at a disadvantage, can interfere with persons ability to walk or stand up, etcetera. in the future I'm sure we will be able to monitor the medial system but now it's not done.
the distincition of pyramidal and non-pyramidal system does not have a foundation in anatomy, the basal ganglia and thalamus process information from the motor cortex and then send it back for processing, a feedback loop. this is very important because now we know that the descending pathways carry information from the motor cortex and information has been further processed information. so there is no distinction between what comes directly from the motor cortex and what has been processed by the basal ganglia. the motor cortex issues commands and the basal ganglia and thalamus process it they just command it from the cortex. these nuclei have different names of course and are organized in groups.
chapter 6 part 1 end
Chapter 6 part 2 begin
motoneurons redeive excitiatory input from muscle spindles (length) and inhibitory input from tendon organs (tension)
why are we so interested in monitoring the motor system?
the ventral part of the spinal cord and ventral horns has a different blood supply from the dorsal or sensory part which is monitoried by somatosensory evoked potentials. this is why it is important to monitor both.
mainly two sources, the anterior spinal artery, posterior spinal artery and segmental arteries. again there is a large degree of individual variability.
collateral supply is common but not universal.
activation of motor tracts; transcranial electrical stimulation of the motor cortex and transcranial magnetic stimulation doesn't give any pain is harmless and efficient, when this was taken to the ooperating room, it didn't work, so we use electrical stimulation of the spinal cord.
alpha motorneurons need facilitated activation which is suppressed by anesthesia.
recording of responses
electroymyogrphic potentials, compound action potentials from motor nerves, cannot be used with muscle relaxant. compound muscle action potentials.
D and I waves are generated by descending activity of the corticospinal tract and caused by activity of neurons in the primary cortex, D waves are Direct electrical stimulation,
recordings from the surface of the spinal cord in a 14 year old patient undergoing a scoliosis operation. transcranial electrical stimulation at different strengths.
spearated in time from two or three i waves; d waves are produced by cells that give rise to descending fibers and i waves are assumed to be other cells in the motor cortex in the cerebellum. the electrode placement on the scalp and vertex will give d waves and i waves but using c1 c2 will give d waves but not i waves showing that generators are electrically different.
train of pulses is more appropriate to activate alpha motor neurons especially when under anesthesia, it is the normal background excitiatory facilitory input that is suppressed by anesthesia which can be compensated by a train of impulses because the excitatory post synaptic potentials will add due to temporal summation. the effect of repetition rate of transcranial electrical stimulation and the number of impulses applied on the responses from the thenar muscle
and the effect of pulse width and current intensity
repeating trains of stimuli can increase the EMG responses from the right abductor hallucis brevis in response to trains of five elctrical impulses to the scalp.
descending motor activity is affected by attention! if they think of something else the response will go down, this is during magnetic stimulation of the motor cortex in an awake individual.
End of Chapter 6 part 2
motoneurons redeive excitiatory input from muscle spindles (length) and inhibitory input from tendon organs (tension)
why are we so interested in monitoring the motor system?
the ventral part of the spinal cord and ventral horns has a different blood supply from the dorsal or sensory part which is monitoried by somatosensory evoked potentials. this is why it is important to monitor both.
mainly two sources, the anterior spinal artery, posterior spinal artery and segmental arteries. again there is a large degree of individual variability.
collateral supply is common but not universal.
activation of motor tracts; transcranial electrical stimulation of the motor cortex and transcranial magnetic stimulation doesn't give any pain is harmless and efficient, when this was taken to the ooperating room, it didn't work, so we use electrical stimulation of the spinal cord.
alpha motorneurons need facilitated activation which is suppressed by anesthesia.
recording of responses
electroymyogrphic potentials, compound action potentials from motor nerves, cannot be used with muscle relaxant. compound muscle action potentials.
D and I waves are generated by descending activity of the corticospinal tract and caused by activity of neurons in the primary cortex, D waves are Direct electrical stimulation,
recordings from the surface of the spinal cord in a 14 year old patient undergoing a scoliosis operation. transcranial electrical stimulation at different strengths.
spearated in time from two or three i waves; d waves are produced by cells that give rise to descending fibers and i waves are assumed to be other cells in the motor cortex in the cerebellum. the electrode placement on the scalp and vertex will give d waves and i waves but using c1 c2 will give d waves but not i waves showing that generators are electrically different.
train of pulses is more appropriate to activate alpha motor neurons especially when under anesthesia, it is the normal background excitiatory facilitory input that is suppressed by anesthesia which can be compensated by a train of impulses because the excitatory post synaptic potentials will add due to temporal summation. the effect of repetition rate of transcranial electrical stimulation and the number of impulses applied on the responses from the thenar muscle
and the effect of pulse width and current intensity
repeating trains of stimuli can increase the EMG responses from the right abductor hallucis brevis in response to trains of five elctrical impulses to the scalp.
descending motor activity is affected by attention! if they think of something else the response will go down, this is during magnetic stimulation of the motor cortex in an awake individual.
End of Chapter 6 part 2
Chapter 6 part 3
Descending motor activity is affected by anesthesia.
purpose of anesthesia is to keep the patient unconscious, pain-free and to keep the patient from moving.
pathways where only few synapses are involved are effected less than where many synapses are involved, this is importnat to consider. it is not so much the direct pathway from cortex to muscles that are affected but pathways that supply alpha motor neurons with the facilitory input that is necessary that a command from the cortex can elicit a motor contraction. the same is of course for sensory systems such as auditory brainstem evoked potentials then it is apparent that anesthetic does not affect these potentials very much because there are few synapses involved.
what can different types of anesthetic do to muscle contractions and d and i waves?
halogenated agent can affect the compound muscle action potential and it's naturally so the effect increases with the concentration of gas. these halogenated agents.
etomidate can enhance signals
Propofol is in a mixutre of oil, TIVA, used in general surgery, has had very little problems or risk of serious complications many of these modern anesthetics will have hallucinations after they wake up. also happens with propofol but seems to disappear in short time. has the same effect on D waves which are well preserved but the I waves are not.
Spinal cord ends at T12-L1 so pedicle screws below this area will not be affected by screws but below could be a problem with the roots, the screws are electrically conducted and connected to an electric stimulator and then placed monitoring of EMG potentials from respective muscles at the same time. if stimulates low will be close to the root. have to remember that the amount of current that is passed through the screw can show how far away the nerve can be stimulated. can be able to stimulate at a sufficient distance, therefore important to keep the current steady. naturally also important to know which muscles to record from, this depends on which root innervates where.
Descending motor activity is affected by anesthesia.
purpose of anesthesia is to keep the patient unconscious, pain-free and to keep the patient from moving.
pathways where only few synapses are involved are effected less than where many synapses are involved, this is importnat to consider. it is not so much the direct pathway from cortex to muscles that are affected but pathways that supply alpha motor neurons with the facilitory input that is necessary that a command from the cortex can elicit a motor contraction. the same is of course for sensory systems such as auditory brainstem evoked potentials then it is apparent that anesthetic does not affect these potentials very much because there are few synapses involved.
what can different types of anesthetic do to muscle contractions and d and i waves?
halogenated agent can affect the compound muscle action potential and it's naturally so the effect increases with the concentration of gas. these halogenated agents.
etomidate can enhance signals
Propofol is in a mixutre of oil, TIVA, used in general surgery, has had very little problems or risk of serious complications many of these modern anesthetics will have hallucinations after they wake up. also happens with propofol but seems to disappear in short time. has the same effect on D waves which are well preserved but the I waves are not.
Spinal cord ends at T12-L1 so pedicle screws below this area will not be affected by screws but below could be a problem with the roots, the screws are electrically conducted and connected to an electric stimulator and then placed monitoring of EMG potentials from respective muscles at the same time. if stimulates low will be close to the root. have to remember that the amount of current that is passed through the screw can show how far away the nerve can be stimulated. can be able to stimulate at a sufficient distance, therefore important to keep the current steady. naturally also important to know which muscles to record from, this depends on which root innervates where.
screws can be placed in different places and must ask the plan on where surgeon will place screws
stimulator connected to the pedicle screw and electrode placed somewhere else, can show that current can escape from the screw, not all is being transmitted to the nerve root that this screw is in close proximity to but it is shunted away. in operations for skull based tumors, the same problem arises.
there are two ways of stimulating , constant current and constant voltage
constant current is convenient for stimulating peripheral nerve because electrode impedance is likely to change so in order to have constant current pass is suitable.
if fluid is shunting then constant voltage is more appropriate to ensure that the same amount of current flows through. depends on if would be dry or wet, if wet then more current will shunt because more current will be needed that will be lost. if they would have used constant voltage...
E=IR, I = E/R, R = E/I; Voltage = Current x Resistance. many stimulators in the operating room have options for constant current and constant voltage
Chapter 6 end of part 3
stimulator connected to the pedicle screw and electrode placed somewhere else, can show that current can escape from the screw, not all is being transmitted to the nerve root that this screw is in close proximity to but it is shunted away. in operations for skull based tumors, the same problem arises.
there are two ways of stimulating , constant current and constant voltage
constant current is convenient for stimulating peripheral nerve because electrode impedance is likely to change so in order to have constant current pass is suitable.
if fluid is shunting then constant voltage is more appropriate to ensure that the same amount of current flows through. depends on if would be dry or wet, if wet then more current will shunt because more current will be needed that will be lost. if they would have used constant voltage...
E=IR, I = E/R, R = E/I; Voltage = Current x Resistance. many stimulators in the operating room have options for constant current and constant voltage
Chapter 6 end of part 3
Lesson 7 Monitoring Operations in the Skull Base
monitoring of the facial nerve in operations for vestibular schwannoma is a model for monitoring other cranial motor nerves.
how to activate the facial nerfe, electrical stimulation, magnetic stimulation, etc.
monopolar and bipolar, need to omit muscle relaxant obviously
preservation of the facial nerve in operations for vestibular schwannoma
identification regions of the tumor where there is no part of the facial nerve present
identification of all of the parts of the facial nerve
monitoring of mechanical induced facial nerve stimulation
monitoring of injury induced facial nerve activation
stimulation want passed stimulator to identify, usually with constant current type.
find the location of the facial nerve.
vary the strength of the stimulation to obtain less than maximal responses
not change in amplitude as stimulating electrode is removed
increased amplitude of EMG means that the electrode was moved towards the facial nerve
decreased amplitude of EMG means that the electrode is moved away from the facial nerve.
Surgeons want to be fast, use as little time as possible.
use of partial muscle relaxation is bad because it is difficult to maintain low level of muscle relaxation, will prevent repetitive muscle contractions. questionable whether partial muscle relaxation offers any protection of the patient from moving. never use any muscle relaxation when the facial nerve is being monitored.
use of emg for decision making regarding grafting?
electrophysiologic methods cannot distinguis between neurapraxia, axonotmesis or neurotmesis
End of Chapter 7 part 1
monitoring of the facial nerve in operations for vestibular schwannoma is a model for monitoring other cranial motor nerves.
how to activate the facial nerfe, electrical stimulation, magnetic stimulation, etc.
monopolar and bipolar, need to omit muscle relaxant obviously
preservation of the facial nerve in operations for vestibular schwannoma
identification regions of the tumor where there is no part of the facial nerve present
identification of all of the parts of the facial nerve
monitoring of mechanical induced facial nerve stimulation
monitoring of injury induced facial nerve activation
stimulation want passed stimulator to identify, usually with constant current type.
find the location of the facial nerve.
vary the strength of the stimulation to obtain less than maximal responses
not change in amplitude as stimulating electrode is removed
increased amplitude of EMG means that the electrode was moved towards the facial nerve
decreased amplitude of EMG means that the electrode is moved away from the facial nerve.
Surgeons want to be fast, use as little time as possible.
use of partial muscle relaxation is bad because it is difficult to maintain low level of muscle relaxation, will prevent repetitive muscle contractions. questionable whether partial muscle relaxation offers any protection of the patient from moving. never use any muscle relaxation when the facial nerve is being monitored.
use of emg for decision making regarding grafting?
electrophysiologic methods cannot distinguis between neurapraxia, axonotmesis or neurotmesis
End of Chapter 7 part 1
Chapter 7 part 2
the trigeminal nerve may be involved in operations for vestibular schwannoma. the trigeminal nerve travels rostral, innervations is great and lots of times it is located closely to 7 and 8 nerve. that means that the trigeminal nerve may be involved in a large acoustic tumor. since it has a motor part, electrical stimulation would cause contraction of muscles that are innervated by the trigeminal nerve, these muscles are the masseter and temporalis muscles, the muscles of mastication, ask patient to bite down on something to be able to distinguish activity.
there is a differnce in stimulation activity for 7 and 5
practical way of displaying ABR for intraoperative monitoring in an operation for vestibular schwannoma, vertex positivity is displayed downard, this should all be seen in about 10ms!
End of Chapter 7 part 2
the trigeminal nerve may be involved in operations for vestibular schwannoma. the trigeminal nerve travels rostral, innervations is great and lots of times it is located closely to 7 and 8 nerve. that means that the trigeminal nerve may be involved in a large acoustic tumor. since it has a motor part, electrical stimulation would cause contraction of muscles that are innervated by the trigeminal nerve, these muscles are the masseter and temporalis muscles, the muscles of mastication, ask patient to bite down on something to be able to distinguish activity.
there is a differnce in stimulation activity for 7 and 5
practical way of displaying ABR for intraoperative monitoring in an operation for vestibular schwannoma, vertex positivity is displayed downard, this should all be seen in about 10ms!
End of Chapter 7 part 2
Chapter 7 part 3
recording from extraocular muscles, place needle electrodes percutaneously so they come close to respective muscles
medial rectus for CNIII
Lateral rectus for CN VI
Superior oblique for CN IV
the extraocular muscles are difficult to place,
typical placements of recording electrodes used in skull base operations, recording from extraocular muscles: place needle electrodes percutaneously so they come close to respective muscles.
recording from extraocular muscles, place needle electrodes percutaneously so they come close to respective muscles
medial rectus for CNIII
Lateral rectus for CN VI
Superior oblique for CN IV
the extraocular muscles are difficult to place,
typical placements of recording electrodes used in skull base operations, recording from extraocular muscles: place needle electrodes percutaneously so they come close to respective muscles.
Monitoring other cranial motor nerves
Lower cranial motor nerves IX, X, XI and XII
Lower cranial motor nerves IX, X, XI and XII
monitoring X can be done by placing electrodes near vocal chords
Monitoring of ABR can detect manipulations of the brainstem before cardiovascular signs change. it takes a good deal of manipulations of the brainstem. we use the monitoring of the ABR because there are many nuclei in the brainstem that are sensitive to manipulations, we would expect that the ABR would change if the brainstem is manipulated.
amplitude of peak 5 amplitude changes differently with blood pressure and heart rate. V can change before heart rate change in 2/3 of cases and before blood pressure changes. most changes happen before or at the same time.
End of Chapter 7 Part III
amplitude of peak 5 amplitude changes differently with blood pressure and heart rate. V can change before heart rate change in 2/3 of cases and before blood pressure changes. most changes happen before or at the same time.
End of Chapter 7 Part III
Chapter/Lesson 8 Practical Aspects of IONM, Working in the OR and the History of IONM
electrical potentials of various kinds
Electrophysiologic recordings in an electrically hostile environment; 60Hz noise from the room and also from other instruments, microscope, none of them have a standard for the electrical fields that others are allowed to omit.
Electrophysiologic recordings in an anesthetized patients.
The need to obtain interpretable records in a short time
interpretation of results must occur promptly
what changes to report and what not to report
communication with the surgeon
relation with the anesthesia team
relations with other members of the operating room team
walking into an operating room before you have done any neuromonitoring, equipment can omit electrostatic
EEG tells the signature of interference; averaged potentials do not.
Find out if there is interference, an antenna connected to the potentials picked up, when the antenna increases then it is going toward the source.
electrical potentials of various kinds
Electrophysiologic recordings in an electrically hostile environment; 60Hz noise from the room and also from other instruments, microscope, none of them have a standard for the electrical fields that others are allowed to omit.
Electrophysiologic recordings in an anesthetized patients.
The need to obtain interpretable records in a short time
interpretation of results must occur promptly
what changes to report and what not to report
communication with the surgeon
relation with the anesthesia team
relations with other members of the operating room team
walking into an operating room before you have done any neuromonitoring, equipment can omit electrostatic
EEG tells the signature of interference; averaged potentials do not.
Find out if there is interference, an antenna connected to the potentials picked up, when the antenna increases then it is going toward the source.
An electric field can also cause interference and the piece of equipment, blood warmers are controlled by measuring the temperature of the blood or they may distort the wave form of the power line.
it is important to reduce the noise as much as possible at the source, electrical noise must be reduced as much as possible. wires should be as short as possible, twisted together or braided together with no loops which will pick up interference and turn it into an electrical signal.
Have a plan of what to do for neuromonitoring, what is to be done before entering the operating room and confirming with the surgeon. the interpretation of results should occur promptly. prepare yourself ahead of time so you understand the recordings and their interpretations. understand the different kinds of changes that can occur and their meaning with regard to pathologies.
What is important to the surgeon, only which information that is of value; changes in recorded potentials, all unusual events. In case of dramatic changes, first assume a biologic cause and always notify the surgeon immediately, then check the equipment, etcetera. changes in the recorded potentials that are larger than normal.
surgeons aren't neurophysiologists, they shouldn't know as much about neurophysiology than neurophysiologists. do not report data without interpretation, a stream of numbers without interpretation is of little value. know what the different steps are, there is a guide here:
EVOKED POTENTIALS
Sensory Evoked Potentials - would you look at latency changes or amplitude changes. people have traditionally looked more at latency than amplitude, the amplitudes tend to fluctuate. better to do the baseline in the operating room with the patient anesthetized but before skin was cut. how do you want to keep your baseline? Keep it superimposed as a certain color or show on. , many use waterfall, stack displays but it is a good thing for documenting but not to look at, what you really want to know is how did the potentials change before the operation began,
Non-pathologic changes
change in anesthesia
change in body temperature
patient position is a critical thing that many times the position on the operating table can cause the brachial plexus to be strectched so it's important to know when they're doing positioning.
irrigation can change the environment, for example, irrigating in the cerebello-pontine angle with a syringe is not a good idea because it can damage the auditory nerve. even peripheral nerves could get hurt with a syringe.
End of Chapter 8 Part I
it is important to reduce the noise as much as possible at the source, electrical noise must be reduced as much as possible. wires should be as short as possible, twisted together or braided together with no loops which will pick up interference and turn it into an electrical signal.
Have a plan of what to do for neuromonitoring, what is to be done before entering the operating room and confirming with the surgeon. the interpretation of results should occur promptly. prepare yourself ahead of time so you understand the recordings and their interpretations. understand the different kinds of changes that can occur and their meaning with regard to pathologies.
What is important to the surgeon, only which information that is of value; changes in recorded potentials, all unusual events. In case of dramatic changes, first assume a biologic cause and always notify the surgeon immediately, then check the equipment, etcetera. changes in the recorded potentials that are larger than normal.
surgeons aren't neurophysiologists, they shouldn't know as much about neurophysiology than neurophysiologists. do not report data without interpretation, a stream of numbers without interpretation is of little value. know what the different steps are, there is a guide here:
EVOKED POTENTIALS
Sensory Evoked Potentials - would you look at latency changes or amplitude changes. people have traditionally looked more at latency than amplitude, the amplitudes tend to fluctuate. better to do the baseline in the operating room with the patient anesthetized but before skin was cut. how do you want to keep your baseline? Keep it superimposed as a certain color or show on. , many use waterfall, stack displays but it is a good thing for documenting but not to look at, what you really want to know is how did the potentials change before the operation began,
Non-pathologic changes
change in anesthesia
change in body temperature
patient position is a critical thing that many times the position on the operating table can cause the brachial plexus to be strectched so it's important to know when they're doing positioning.
irrigation can change the environment, for example, irrigating in the cerebello-pontine angle with a syringe is not a good idea because it can damage the auditory nerve. even peripheral nerves could get hurt with a syringe.
End of Chapter 8 Part I
Chapter 8 Part 2
False positives and False negatives, false positive means the test tells that there is disease present when their isn't. false negative says there isn't disease when their is disease present, meaning it escapes medical tests. there is a limited relevance for intraoperative monitoring. we are most interested in preventing post operative deficits. false negative means something changed that was not observed in the monitoring. that did not cover that area where the changes occurred.
End of Part 2
False positives and False negatives, false positive means the test tells that there is disease present when their isn't. false negative says there isn't disease when their is disease present, meaning it escapes medical tests. there is a limited relevance for intraoperative monitoring. we are most interested in preventing post operative deficits. false negative means something changed that was not observed in the monitoring. that did not cover that area where the changes occurred.
End of Part 2
Chapter Part 3 Remember the nurses control the environment, don't be afraid to lend a helping hand, it keeps good relationships with people. the nurses, anesthesiologists, doctors are to provide the best possible care for the patient.
The neurophysiologist should always be in the operating room. the person responsible should be physically present in the operating room
End of part 3
The neurophysiologist should always be in the operating room. the person responsible should be physically present in the operating room
End of part 3
END of Chapter 8 Part 4 Aage Moller