An initial investigation of bispectral monitoring as an adjunct to nurse-administered propofol sedation for colonoscopy

BACKGROUND AND AIMS: Bispectral (BIS) monitoring has been used to evaluate depth of sedation in intensive care and surgical patients. We sought to explore its utility as a monitoring device for nurse-administered propofol sedation (NAPS) during colonoscopy. METHODS: Fifty consecutive patients (ASA I or 11) receiving NAPS for outpatient colonoscopy were evaluated. BIS scores, sedation scores, and propofol dosing were correlated. The nurses assessed the usefulness of BIS by questionnaire. RESULTS: The mean (SD) dose of propofol required to produce a BIS value < 60 was 109.4 (43.9) mg and an Observer's Assessment of Alertness/Sedation (OAA/S) score of 1 (deep sedation) was 91.4 (44.8) mg (p < 0.0001). The mean times required to achieve BIS values < 60 (188 +/- 147.1 s) and < 70 (164.3 +/- 95.1 s) were significantly longer than the mean time required to achieve an OAA/S of 1 (117.4 +/- 93.0 s, p = 0.0007). Similarly, during the recovery phase, there was a lag time of 197.9 s between mean (SD) time required from the last dose of propofol to an OAA/S of 5 (372.1 197.1 s) and the mean (SD) time required from the last dose of propofol to a BIS value greater than or equal to 90 or return to baseline (570 +/- 279.9 s, p < 0.0001). The mean (SD) BIS value in the maintenance phase of sedation was 58.9 (8.53), with a range of 22-88. Nurses administering propofol rated the usefulness of BIS at a mean of 2.85 (maximum usefulness scored as 4) in guiding the dosing of propofol sedation during the maintenance phase of sedation. No patient required mask ventilation or endotracheal intubation. CONCLUSIONS: The BIS index in its current version is not useful in titrating boluses of propofol to an adequate level of sedation, because there is a substantial lag time between decrease of BIS scores to <70 and OAA/S scores indicative of deep sedation. There is also a substantial lag time between recovery of alertness and return of BIS scores to normal. A controlled trial of whether BIS values can assist in avoiding unnecessary propofol dosing during the maintenance phase of sedation appears warranted.