General anesthesia occurs frequently in elderly patients during propofol-based sedation and spinal anesthesia

Study Objective: To test the hypothesis that sedation in elderly patients is often electrophysiologically equivalent to general anesthesia (GA). Design: Prospective, observational study. Setting: Operating room of a university medical center. Patients: 40 elderly patients (≥65 yrs of age) undergoing hip fracture repair with spinal anesthesia and propofol-based sedation. Interventions: In the routine practice group (RP; n = 15), propofol sedation was administered per the usual routine of the anesthesiologist. In the targeted sedation group (TS; n = 25), sedation was titrated to an observer's assessment of alertness/sedation (OAA/S) score of 4 (ie, lethargic in response to name called) to 5 (ie, awake and alert). Measurements: Both patient groups underwent processed electroencephalographic monitoring using bispectral index (BIS) intraoperatively. BIS levels were compared between groups to determine amount of surgical time spent in GA (BIS ≤ 60). Main Results: In the RP group, subjects spent 32.2% of surgical time at BIS levels consistent with GA. Although averaged BIS values during surgery increased from (mean ± SD) 71 ± 16 to 88 ± 9 (P < 0.001), GA was still observed during 5% of surgical time in the TS group. Overall, 13 of 15 (87%) RP group patients and 11 of 25 (44%) TS group patients (P < 0.010) experienced some period of GA. Conclusions: BIS levels consistent with GA occur frequently in elderly patients during propofol-based sedation for spinal anesthesia. Altering routine practice such that sedation is titrated to a targeted clinically-determined sedation level reduces - but does not eliminate - this incidence.