Aortic Arch Replacement
This 72-year-old man with a history of COPD and no prior cardiac history underwent CT of the abdomen/pelvis for follow-up evaluation of known left adrenal adenoma (benign) and small hepatic and renal cysts. During this exam he was found to have a 5 cm aneurysm at the level of the diaphragm. He was referred to cardiovascular surgery and chest CT angiography showed an ascending aortic aneurysm beginning at the aortic valve measuring 8.3 cm and extending into the aortic arch and 5 cm of the descending aorta. He also has moderate-severe aortic insufficiency, and has recently complained of fatigue and chest pressure with exertion. He is now undergoing replacement of his ascending arch and aortic valve with deep hypothermia and circulatory arrest. This procedure carries attendant risks of cerebral ischemia, therefore EEG and SEP monitoring was requested by the surgeon to ensure an isoelectric EEG before circulatory arrest.
07:05 - Sterile needle electrodes were placed at the following locations of the International 10-20 system: F3, F4, F7, F8, T3, C3’, C4’, T4, T5, P3, P4, T6, O1, and O2. An 8-channel bipolar montage was used: F7-T3, F3-C3, T3-T5, P3-O1, F8-T4, F4-C4, T4-T6, and P4-O2, Raw EEG was displayed on a Cadwell Cascade system, as well as processed EEG, including CSA, DSA, and left/right asymmetry, in order to detect any EEG slowing or asymmetry associated with vascular insufficiency. Stimulating electrodes were placed over the left and right ulnar and posterior tibial nerves and cortical responses recorded from scalp electrodes C3’, C4’, and Cz’, referred to Fpz, and subcortical responses from an electrode over the cervical spine.
08:15 - Pre-incision baselines obtained: EEGs are symmetrical, showing primarily low voltage slow activity on all channels. Excessive 60 Hz activity seen, cannot ascertain source, notch filters on. SEPs show robust responses from stimulation of all four extremities: left ulnar nerve - N20 - 20.0 ms /2.20 uvolts, right ulnar nerve N20 - 22.3 ms /1.92 uvolts, left posterior tibial nerve P50 - 50.0 ms /3.64 uvolts, right posterior tibial nerve P50 - 49.8 ms /1.98 uvolts. The cervical N13 was obscured by excessive 60 Hz artifact (cannot use notch filter on SEP channels).
09:47 - On bypass, begin cooling. Nasopharyngeal temperature now at 33.9 C.
09:54 - SEPs lost, EEG activity still present, temperature at 31.7 C.
09:58 - Temperature now at 29.2 C, EEGs are mostly flat with occasional activity.
10:03 - Temperature now at 26.5 C, EEGs still showing occasional complexes.
10:13 - Temperature now at 23.2 C. EEGs now in electro-cerebral silence, as well as can be determined given high artifact levels. Results reported to surgeon.
10:19 - Surgeon confirms EEGs still showing electro-cerebral silence.
10:20 - Very occasional EEG waves seen, > 95% silence. Temperature at 22.9 C.
10:32 - Begin slow re-warming.
10:42 - Temperature now at 24.9 C, more EEG activity noted. Surgeon informed, states that circulatory arrest will not be necessary so some EEGs are OK.
10:44 - Reappearance of left posterior tibial nerve SEPs at 74.6 ms (!). Temperature at 25.2 C.
10:52 - Now seeing stretches of several seconds of continuous EEG, still periods of electro-cerebral silence in between. Temperature at 25.8 C. SEPs now evident from all four extremities, very delayed.
11:15 - Replacing aortic valve. EEGs/SEPs as before, all four SEPs slowly returning toward baseline latencies, EEGs still showing periods of electro-cerebral silence intermixed with low voltage slow waves.
07:05 - Sterile needle electrodes were placed at the following locations of the International 10-20 system: F3, F4, F7, F8, T3, C3’, C4’, T4, T5, P3, P4, T6, O1, and O2. An 8-channel bipolar montage was used: F7-T3, F3-C3, T3-T5, P3-O1, F8-T4, F4-C4, T4-T6, and P4-O2, Raw EEG was displayed on a Cadwell Cascade system, as well as processed EEG, including CSA, DSA, and left/right asymmetry, in order to detect any EEG slowing or asymmetry associated with vascular insufficiency. Stimulating electrodes were placed over the left and right ulnar and posterior tibial nerves and cortical responses recorded from scalp electrodes C3’, C4’, and Cz’, referred to Fpz, and subcortical responses from an electrode over the cervical spine.
08:15 - Pre-incision baselines obtained: EEGs are symmetrical, showing primarily low voltage slow activity on all channels. Excessive 60 Hz activity seen, cannot ascertain source, notch filters on. SEPs show robust responses from stimulation of all four extremities: left ulnar nerve - N20 - 20.0 ms /2.20 uvolts, right ulnar nerve N20 - 22.3 ms /1.92 uvolts, left posterior tibial nerve P50 - 50.0 ms /3.64 uvolts, right posterior tibial nerve P50 - 49.8 ms /1.98 uvolts. The cervical N13 was obscured by excessive 60 Hz artifact (cannot use notch filter on SEP channels).
09:47 - On bypass, begin cooling. Nasopharyngeal temperature now at 33.9 C.
09:54 - SEPs lost, EEG activity still present, temperature at 31.7 C.
09:58 - Temperature now at 29.2 C, EEGs are mostly flat with occasional activity.
10:03 - Temperature now at 26.5 C, EEGs still showing occasional complexes.
10:13 - Temperature now at 23.2 C. EEGs now in electro-cerebral silence, as well as can be determined given high artifact levels. Results reported to surgeon.
10:19 - Surgeon confirms EEGs still showing electro-cerebral silence.
10:20 - Very occasional EEG waves seen, > 95% silence. Temperature at 22.9 C.
10:32 - Begin slow re-warming.
10:42 - Temperature now at 24.9 C, more EEG activity noted. Surgeon informed, states that circulatory arrest will not be necessary so some EEGs are OK.
10:44 - Reappearance of left posterior tibial nerve SEPs at 74.6 ms (!). Temperature at 25.2 C.
10:52 - Now seeing stretches of several seconds of continuous EEG, still periods of electro-cerebral silence in between. Temperature at 25.8 C. SEPs now evident from all four extremities, very delayed.
11:15 - Replacing aortic valve. EEGs/SEPs as before, all four SEPs slowly returning toward baseline latencies, EEGs still showing periods of electro-cerebral silence intermixed with low voltage slow waves.