Erroneous Conclusion from Processed Electroencephalogram with Changing Anesthetic Depth

Abstract

Intraoperative monitoring of the electroencephalogram (EEG) is commonly used for detection of cerebral ischemia during carotid endarterectomy. Although real-time interpretation of analog EEG recordings may be considered the "gold standard" for ischemia detection, various signal-processing techniques have been used to ease the interpretation of intraoperative EEG. Several reviews of various EEG-processing techniques are now available. 1,2 Appropriate monitoring of intraoperative EEG for cerebral ischemia assumes that anesthetic depth remains relatively constant, because changes in anesthetic depth or surgical stimulation are known to have profound effects on the EEG. 3 We report the case of a patient having a carotid endarterectomy in which the processed EEG showed a significant loss of "power," and a shift of the spectral edge frequency to lower frequencies during anesthetic emergence. If the EEG had been recorded under conditions of a stable anesthetic when the carotid artery was clamped, the record could have been interpreted as cerebral ischemia. Case ReportA 65-yr-old woman with a history of hypertension and asymptomatic bilateral 90% carotid artery stenosis presented for elective right carotid endarterectomy. Routine physical examination, laboratory values, electrocardiogram, and chest radiograph were otherwise within normal limits.In addition to application of routine monitors, a left radial artery catheter was inserted. EEG electrodes were placed in an approximation of the International 10-20 system using an electrode-embedded nylon cap (Electro-cap International Inc., Eaton, OH). An eight-channel EEG (Neurotrac II, Moberg Medical, Ambler, PA) in a monopolar montage (F3, F4, C3, C4, P3, P4, T5 and T6 referred to CZ) was recorded continuously and stored digitally. Low-and high-filter settings were 0.5 and 30 Hz, respectively. A 2 MHz-pulse wave transcranial Doppler (TCD) probe (Multigon Industries Inc., Yonkers, NY) was applied over the right temporal window to insonate the ipsilateral middle cerebral artery.Following intravenous 100 µg fentanyl and 2 mg midazolam, general anesthesia was induced using 250 mg sodium thiopental, and tracheal intubation was facilitated with succinylcholine. Anesthesia was maintained using N 2 O and isoflurane. Neuromuscular blockade was achieved with 10 mg vecuronium and reversed with 3.5 mg neostigmine and 0.6 mg glycopyrrolate. All hemodynamic and anesthetic data were monitored continuously and recorded every minute by a computer-based data acquisition system (Lifelog from MI 2 , Rosemont, PA).The patient underwent a routine carotid endarterectomy with general anesthesia. Before and after application of the carotid cross clamps, systolic blood pressure was maintained within the patient's normal range between 120 and 150 mmHg. Phenylephrine was used to increase systolic blood pressure to approximately 180 mmHg during carotid artery cross clamping. Because there were no EEG changes indicative of ischemia with carotid artery clamping, no shunt was inserted (fig. 1, upper; precl...

Cerebral Injury Predicted by Transcranial Doppler Ultrasonography But Not Electroencephalography During Carotid Endarterectomy

“…The reliability of EEG monitoring depends on three major factors: the number of channels (with 16 being ideal, but seldom possible in the majority of operating rooms), the experience level of the observer, and the depth of anesthesia (14,15). Sometimes EEG changes arise from causes other than cerebral ischemia, as we have already reported in one example (16). Similarly, while TCD is used to measure CBF changes in the operating room during CEA because it is a continuous noninvasive monitor of CBF in the MCA, it is also subject to misinterpretation and may lack sensitivity and specificity (17).…”

Souffrance cérébrale sous anesthésie générale: que peut-on attendre de la surveillance de l’EEG?

“…1 3 Spectral analysis produced poor results during cardiac 14 or carotid surgery. 10 Aperiodic analysis, using the Lifescan™ monitor (Diatek, San Diego, CA, USA) in carotid surgery, also produced a number of false negative and a few false positive results. 15,16 In summary, classical EEG monitoring is not absolutely reliable to detect brain injury.…”