Frequency and clinical impact of preserved bispectral index activity during deep sedation in mechanically ventilated ICU patients

Objective Despite an overall correlation between the bispectral index of the EEG (BIS) and clinical sedation assessment, unexpectedly high BIS values can be observed at deep sedation levels. We assessed the frequency, interindividual variability and clinical impact of high BIS values during clinically deep sedation. Design and setting Prospective observational study in two university-affiliated intensive care units. Patients Sixty-two mechanically ventilated patients requiring intravenous sedation and analgesia for ≥24 h. Measurements and main results Paired measurements of BIS and sedation measured on the adaptation to intensive care environment (ATICE) score were obtained every 3 h until awakening. A paired measurement with BIS >60 at deep sedation (ATICE Awakeness ≤2) was defined as discordant. Patients were considered discordant if their individual ratio of number of discordant measurements to number of total measurements during deep sedation was above the median discordance ratio of the overall cohort. At least one discordant assessment was observed in 52 patients (83.9%). Median individual discordance ratio was 32% (14.3–50.0%). Time from awakening to first T-piece trial [16 h (4–34) vs. 46 h (9–109), p = 0.01] and to extubation [35 h (23–89) vs. 88 h (46–152 h), p = 0.05] were significantly shorter in discordant compared to concordant patients. BIS-ATICE discordance was independently associated with successful extubation within 48 h after awakening (OR 6.7, CI 95% 1.8–25.0, p = 0.005). The rate of ICU recall was not different in BIS-ATICE discordant and concordant patients. Conclusions In mechanically ventilated ICU patients, discordance between high BIS values and deep clinical sedation is frequently observed and may suggest faster weaning from the ventilator.