An evaluation of sedation level using bispectral index (BIS) and correlated adverse events in patients undergoing colonoscopies

The purpose of this prospective, observational study was to provide data for anesthesia providers on current sedation practices during elective colonoscopies. This included determining the incidence of general anesthesia (GA) and the presence or absence of correlated adverse events. Additionally, this research considered if patients who are commonly consented for a MAC anesthetic should be more appropriately consented for GA. Participants (N = 39) consisted of a convenience sampling of physical status (PS) I, II, and III patients scheduled for elective colonoscopies and undergoing sedation with propofol. Data was collected by researchers over a four-week period at a non-teaching rural hospital in Western North Carolina. A bispectral index (BIS) monitor was used to monitor the depth of sedation and values were utilized to determine possible correlated adverse events. Statistical analysis showed that 100% (39/39) of patients reached levels of GA (i.e., BIS = 60) at some point during their procedure. Variables that showed a significant correlation with the occurrence of GA were smaller body mass index (BMI) (r = -.42, r2 = .17, p = .008), longer length of procedure (r = .85, r2 = .72, p < .001), and the number of minutes patients experienced an absent end tidal carbon dioxide (ETCO2) (i.e., apnea) waveform (r = .49, r2 = .24, p = .002). Additionally, greater BMI correlated with a greater nadir BIS value obtained throughout the entire procedure (r = .54, r2 = .29, p < .001), and was found to correlate with less time at BIS values = 40 (r = -.51, r2 = .26, p < .001). Longer procedures correlated with more minutes spent with BIS values = 40 (r = .43, r2 = .18, p = .007), and more minutes with absent ETCO2 waveform (r = .52, r2 = .27, p = .001); however, these findings were clinically insignificant since only one absent ETCO2 waveform actually resulted in a decrease in saturation of peripheral oxygen (SpO2) to = 90% (i.e., hypoxia), which quickly resolved with a chin lift. Additionally, the number of minutes with SpO2 = 90% was not significantly correlated with the minutes of GA (r = -.17, r2 = .03, p = .299). The results of this study indicate, in patients scheduled for colonoscopies who are consented for IV GA, it is common for anesthesia providers to consistently deliver a level of sedation concordant with GA. The significance of this finding relates to the pre-study clinical observation, that endoscopic patients being consented for anesthesia designated as MAC with IV sedation, actually demonstrate intraoperative signs of GA similar to what were observed in this study. Future studies are warranted to determine the frequency of the various forms of anesthesia consent obtained for elective colonoscopies, along with research that assesses anesthetic depth with BIS monitoring in patients consented for MAC with IV sedation. Such research would help to further enhance patient safety and address potential medical legal concerns