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74s Neurophysiol Clin (1990) 20, S, 74s-76s © Elsevier, Paris Communications affich4es Posters SESSION 11 Monitorage EEP et PE en soins intensifs et en chirurgie EEG and EPs monitoring in intensive care and surgery P107 LIGHT ANESTHESIA, AWARENESS, AND EEG MONITORING. E.R.J.F. Boezeman, N. van der Ende, S.J. Hengeveld and A.J.R. Simons. Departments of clinical neurophysiology and anesthesiology, St. Antonius Hospital, Koekoekslaan i, 3435 CM Nieuwegein, The Netherlands. In open heart surgery we observed that some cases showed a sudden appearance of alpha-rhythm following a painful stimulus as electrocautery. Alpha-rhythm occurs on the boundery of the state of aetiviation and unconsciousness and may therefore be useful in detecting the moment of transition between these two states. In an experiment during induction of anesthesia, with linearly increasing plasma levels of ethomidate using an open two compartiment model, we asked i0 patients to close their eyes and to press a hand-held button whenever they perceived a loud short lasting tone burst applied in random order through earphones. In all these cases with increasing plasma levels of ethomidate alpha activity was suppressed for 1 to 5 seconds within the first three minutes after induction. This showed up in the visually judged stripehart EEG within 100-200 milliseconds following the stimulus. Thereafter this suppression disappeared but our patients were still capable to press the button, i.e., being aware of the stimulus. Within 2 minutes more significant EEG changes developed, and the time it took to press the button became longer whereupon this reaction finally stopped. The alpha suppression is very likely the very first sign in EEG recordings just before consciousness disappears and real anesthesia begins. During the start of anesthesia, however, the alpha-rhythm can be provoked by the stimulus instead of being suppressed. This may indicate a situation that precedes awareness. P108 REAL-TIME QUANTITATIVE EEG INTRAOFEItA'YIVE MONITORING DURING CAROTID ENDARTERECTOMY L.D. GUGINO, R.J. Chahot, L. AGLIO, R.HEINO, Brigham and Women's Hospital, Boston(USA) EEG monitoring during vascular surgery began in 1957. However, de- spite this fact, EEG monitoring is not accepted standard clinical practise. Reluctance to incorporate this technique into standard surgical protocols may be due to controversy about what degree of EEG changes are critical and concerns about the appropriate number, optimalplacement of electrodes and optimal EEG features to be monitored. Within th]s presentation we describe a real-time quantitative EEG (QEEG) monitoring devise and describe its application during 45 carotid endarterec- tomy procedures. EEG was recorded from 19 monopolar and 8 bipolar derivations with QEEG features calculated on line upon user specified epoch sizes. Features calculated across the standard frequency bands included ab- solute and relative power, amplitude asymmetry, waveform coherence, and a series of multivariate features calculated across cortical leads associated with the perfusion fields of the major cerebral arteries. All features were displayed on-line as raw values or as z-score deviations from a self-normed baseline collected at any user specified time. We will describe QEEC feature changes in 40 carotid endarterectomy procedures, 20 of which required shunt placement and 20 of which were ac- complished without shunt placement. All QEEG features were evaluated at baseline after stable anesthesia was established and at 7 additional time intervals including; (a)prior to carotid clamp placement, (b)three time in- tervals after clamp placement, and (c)three time intervals after shunt place- ment (shunted patients) or three additional comparable time intervals (non- shunted patients). This data will be described with attention paid to deter- mining which QEEG features best reflect cerebral ischemia, which electrodes show changes, and what degree of change reflects a need for shunt placement. These questions will also be addressed by examining QEEG changes in five carotid endarterectomy patients who developed a stroke during the proce- dure.

P107 Light anesthesia, awareness, and EEG monitoring

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Page 1: P107 Light anesthesia, awareness, and EEG monitoring

74s Neurophysiol Clin (1990) 20, S, 7 4 s - 7 6 s

© Elsevier , Pa r i s

C o m m u n i c a t i o n s aff ich4es Posters

S E S S I O N 11

Monitorage E E P et P E en soins intensifs et en chirurgie EEG and EPs monitoring in intensive care and surgery

P107

LIGHT ANESTHESIA, AWARENESS, AND EEG MONITORING. E.R.J.F. Boezeman, N. van der Ende, S.J. Hengeveld and A.J.R. Simons. Departments of clinical neurophysiology and anesthesiology, St. Antonius Hospital, Koekoekslaan i, 3435 CM Nieuwegein, The Netherlands.

In open heart surgery we observed that some cases showed a sudden appearance of alpha-rhythm following a painful stimulus as electrocautery. Alpha-rhythm occurs on the boundery of the state of aetiviation and unconsciousness and may therefore be useful in detecting the moment of transition between these two states. In an experiment during induction of anesthesia, with linearly increasing plasma levels of ethomidate using an open two compartiment model, we asked i0 patients to close their eyes and to press a hand-held button whenever they perceived a loud short lasting tone burst applied in random order through earphones. In all these cases with increasing plasma levels of ethomidate alpha activity was suppressed for 1 to 5 seconds within the first three minutes after induction. This showed up in the visually judged stripehart EEG within 100-200 milliseconds following the stimulus. Thereafter this suppression disappeared but our patients were still capable to press the button, i.e., being aware of the stimulus. Within 2 minutes more significant EEG changes developed, and the time it took to press the button became longer whereupon this reaction finally stopped. The alpha suppression is very likely the very first sign in EEG recordings just before consciousness disappears and real anesthesia begins. During the start of anesthesia, however, the alpha-rhythm can be provoked by the stimulus instead of being suppressed. This may indicate a situation that precedes awareness.

P108

R E A L - T I M E Q U A N T I T A T I V E E E G I N T R A O F E I t A ' Y I V E M O N I T O R I N G D U R I N G C A R O T I D E N D A R T E R E C T O M Y L.D. G U G I N O , R . J . C h a h o t , L. A G L I O , R . H E I N O , Brigham

and Women's Hospital, B o s t o n ( U S A )

EEG monitoring during vascular surgery began in 1957. However, de- spite this fact, EEG monitoring is not accepted s tandard clinical practise. Reluctance to incorporate this technique into s tandard surgical protocols may be due to controversy about what degree of EEG changes are critical and concerns about the appropr ia te number, op t imalp lacement of electrodes and opt imal EEG features to be monitored.

Within th]s presentat ion we describe a real-t ime quanti tat ive EEG (QEEG) monitoring devise and describe its application during 45 carotid endarterec- tomy procedures. EEG was recorded from 19 monopolar and 8 bipolar derivations with QEEG features calculated on line upon user specified epoch sizes. Features calculated across the s tandard frequency bands included ab- solute and relative power, ampl i tude asymmetry , waveform coherence, and a series of multivariate features calculated across cortical leads associated with the perfusion fields of the major cerebral arteries. All features were displayed on-line as raw values or as z-score deviations from a self-normed baseline collected at any user specified time.

We will describe QEEC feature changes in 40 carotid endarterectomy procedures, 20 of which required shunt placement and 20 of which were ac- complished without shunt placement. All QEEG features were evaluated at baseline after stable anesthesia was established and at 7 additional t ime intervals including; (a)prior to carotid clamp placement, (b)three time in- tervals after clamp placement, and (c)three t ime intervals after shunt place- ment (shunted patients) or three addit ional comparable t ime intervals (non- shunted patients). This da ta will be described with a t tent ion paid to deter- mining which QEEG features best reflect cerebral ischemia, which electrodes show changes, and what degree of change reflects a need for shunt placement. These questions will also be addressed by examining QEEG changes in five carot id endarterectomy patients who developed a stroke during the proce- dure.