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BIS™ Variability in the Obtunded and Comatose Patient
Michael C. Woo, M.D.; Sajid Shahul, M.D.; John P. Kress, M.D.; Michael F. O'Connor, M.D.; Jesse Hall, M.D.
Anesthesia and Critical Care, University of Chicago, Chicago, Illinois
Introduction: BIS™ monitoring is increasingly advocated for monitoring conscious sedation in critically ill patients. The BIS™ monitor has been extensively evaluated and validated in a population of mostly healthy patients undergoing general anesthesia. Its performance in metabolic derangement or neurologic injury is unknown. We hypothesize that monitor performance degrades in the setting of severe metabolic derangement or neurologic injury associated with stupor and coma.

Methods: After obtaining IRB approval, we studied 27 patients who had Ramsey scores of 5 or 6. Patients were non-sedated, intubated, mechanically ventilated, and suffering from metabolic derangement or neurologic injury. BIS™ values were recorded during a 15-30 minute observation period, immediately followed by a 5 minute assessment period. Ramsey scores were assessed by an observer blinded to BIS™ values. We used the A-1050 BIS monitor (Aspect Medical Systems) with the most current software available.

We recorded demographics, coexisting diseases, current diagnoses, use of sedative medications, APACHE III scores, modified Ramsey scores, and OAAA/S scores.

Results: In observation period, BIS™ values ranged from 19 to 98 (mean 63, median 58). They were stable in 14 patients. 13 patients' BIS™ values fluctuated over time. Average fluctuaton was an average of +/-7 points, with a range of 2 to 21.

During this undisturbed period, BIS™ values of 7 patients never trended below 85.

During the assessment period, BIS™ values ranged from 32 to 98 (mean 79, median 90). They did not change in 10 patients. 17 patients' BIS™ values fluctuated by at least 2, and up to 50 points. Average fluctuaton was +/-6.

Discussion: We anticipated that BIS™ values >85 in unsedated patients would be associated with higher levels of responsiveness and apparent consciousness than we observed. BIS™ values did not correlate with levels of responsiveness in obtunded and comatose patients.

Anesthesiology 2002; 96: A583
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