SEP RUNOFF
Transmission; generated by a nerve or tract as an action potential is propagated past the recording site, latency is dependent on the distance from site of stimulation to site of recording
bipolar vs referential recordings
bipolar recording electrodes are relatively closely spaced specific far field responses common mode rejected, near field responses recorded referential recording electrodes are spaced relatively far apart sensitive both far-field and near field responses are recorded, less common mode rejection
note that p31 and n34 are absent in the non-cephalic recording, widespread scalp potential
present in the not cephalic to cephalic recordings referential recording
absent in the cephalic to cephalic recordings bipolar recording
anesthetic effects
effects of inhalational agents on ssep responses; cause a dose-dependent decrease in cortical amplitudes and increase cortical latencies
@ 1/2 MAC as increase gases there is a dose dependent latency and amplitude reduction
the effects of nitrous oxide on cortical amplitude amplification with etomidate administration; shows decreasing amplitude with time
Effects of Midazolam injection on SSEP cortical waveforms
warning criteria; greater than 50% amplitude decrease, greater than 10% latency increase
non surgical factors effecting Evoked Potentials; anesthetic changes - cortical waveforms will change in response to increases in the gases boluses and changes in infusion rates or concentrations, BP changes, temperature changes, limb ischemia
When to expect changes - always, you should always remain vigilant when monitoring SSEP responses as changes could occur at any time for numerous reasons, there are 3 types of changes that we may expect to see, systemic, surgical manipulations, technical
periods during procedure to expect changes; intubation especially if the patient has cervical myelopathy, positioning, decompression, placement of distractors, placement of instrumentation, clamping of carotid artery
*LH* round 2
Effects of midazolam (versed) injection on SSEP cortical waveforms; decrease amplitude over time
Change criteria; greater than 50% amplitude decrease; greater than 10% latency increase
Non-surgical factors effecting Evoked potentials; anesthetic changes; cortical waveforms will change in response to increases in the gases, boluses and changes in infusion rates or concentrations, blood pressure changes, temperature changes, limb ischemia
When to expect changes, always you should always remail vigilant when monitoring SSEP responses as changes could occur at any time for numerous reasons. There are 3 types of changes that we may expect to see; systemic; surgical manipulations, technical
Periods during procedure to expect changes; intubation, especially if the patient has cervical myelopathy, positioning, decompression, placement of distractors, placement of instrumentation, clamping of carotid artery
Surgical Procedures where SSEPs are indicated; cervical and thoracic decompressions and fusions, carotid endarterectomies, brainstem procedures, cerebral and aortic aneurysms, lumbar fusions
SEP Runoff
dorsal column / medial lemniscus / thalamus / primary sensory cortex
stimulate the peripheral nerve, record at multiple levels (brachial plexus, medulla, cortex)
small signals, signal averaging required
sensitive to compression of the spinal cord but not spinal ischemia
monitors posterior posterior column function in spine surgery
sensitive to cortical and thalamic ischemia
monitors cerebral perfusion in vascular surgery
can use to map the location of the central sulcus with surface electrodes
useful in positioning of an unstable cervical spine
most common agents lower amplitude and increase latency (the same effects as compromise of neural pathways)
*LH*
Somatosensory Evoked Potentials
Pathways Waveforms and Generators
Goal of SSEP monitoring is during surgery to preserve functional integrity of the peripheral nerve monitored, spinal cord, brain stem and brain (cortical and subcortical structures) to detect injury early before neural damage becomes permanent
how is this accomplished; by stimulating a peripheral nerve distal (caudal) to the surgical site and by recording evoked potentials from the cortical and subcortical structures proximal to the surgical site with the assumption that the spinal cord or other structure at risk must be functioning properly if recording of caudal sensory stimulation can occur caveat intact SSEP responses do not necessarily indicate intact motor pathways
Nerves generally monitored Upper Extremities Median Nerve C5-T1 nerve root innervations; Ulnar nerve C8-T1 nerve root innervations C7-T1 in some patients
Transmission; generated by a nerve or tract as an action potential is propagated past the recording site, latency is dependent on the distance from site of stimulation to site of recording
bipolar vs referential recordings
bipolar recording electrodes are relatively closely spaced specific far field responses common mode rejected, near field responses recorded referential recording electrodes are spaced relatively far apart sensitive both far-field and near field responses are recorded, less common mode rejection
note that p31 and n34 are absent in the non-cephalic recording, widespread scalp potential
present in the not cephalic to cephalic recordings referential recording
absent in the cephalic to cephalic recordings bipolar recording
anesthetic effects
effects of inhalational agents on ssep responses; cause a dose-dependent decrease in cortical amplitudes and increase cortical latencies
@ 1/2 MAC as increase gases there is a dose dependent latency and amplitude reduction
the effects of nitrous oxide on cortical amplitude amplification with etomidate administration; shows decreasing amplitude with time
Effects of Midazolam injection on SSEP cortical waveforms
warning criteria; greater than 50% amplitude decrease, greater than 10% latency increase
non surgical factors effecting Evoked Potentials; anesthetic changes - cortical waveforms will change in response to increases in the gases boluses and changes in infusion rates or concentrations, BP changes, temperature changes, limb ischemia
When to expect changes - always, you should always remain vigilant when monitoring SSEP responses as changes could occur at any time for numerous reasons, there are 3 types of changes that we may expect to see, systemic, surgical manipulations, technical
periods during procedure to expect changes; intubation especially if the patient has cervical myelopathy, positioning, decompression, placement of distractors, placement of instrumentation, clamping of carotid artery
*LH* round 2
Effects of midazolam (versed) injection on SSEP cortical waveforms; decrease amplitude over time
Change criteria; greater than 50% amplitude decrease; greater than 10% latency increase
Non-surgical factors effecting Evoked potentials; anesthetic changes; cortical waveforms will change in response to increases in the gases, boluses and changes in infusion rates or concentrations, blood pressure changes, temperature changes, limb ischemia
When to expect changes, always you should always remail vigilant when monitoring SSEP responses as changes could occur at any time for numerous reasons. There are 3 types of changes that we may expect to see; systemic; surgical manipulations, technical
Periods during procedure to expect changes; intubation, especially if the patient has cervical myelopathy, positioning, decompression, placement of distractors, placement of instrumentation, clamping of carotid artery
Surgical Procedures where SSEPs are indicated; cervical and thoracic decompressions and fusions, carotid endarterectomies, brainstem procedures, cerebral and aortic aneurysms, lumbar fusions
SEP Runoff
dorsal column / medial lemniscus / thalamus / primary sensory cortex
stimulate the peripheral nerve, record at multiple levels (brachial plexus, medulla, cortex)
small signals, signal averaging required
sensitive to compression of the spinal cord but not spinal ischemia
monitors posterior posterior column function in spine surgery
sensitive to cortical and thalamic ischemia
monitors cerebral perfusion in vascular surgery
can use to map the location of the central sulcus with surface electrodes
useful in positioning of an unstable cervical spine
most common agents lower amplitude and increase latency (the same effects as compromise of neural pathways)
*LH*
Somatosensory Evoked Potentials
Pathways Waveforms and Generators
Goal of SSEP monitoring is during surgery to preserve functional integrity of the peripheral nerve monitored, spinal cord, brain stem and brain (cortical and subcortical structures) to detect injury early before neural damage becomes permanent
how is this accomplished; by stimulating a peripheral nerve distal (caudal) to the surgical site and by recording evoked potentials from the cortical and subcortical structures proximal to the surgical site with the assumption that the spinal cord or other structure at risk must be functioning properly if recording of caudal sensory stimulation can occur caveat intact SSEP responses do not necessarily indicate intact motor pathways
Nerves generally monitored Upper Extremities Median Nerve C5-T1 nerve root innervations; Ulnar nerve C8-T1 nerve root innervations C7-T1 in some patients