Optimal propofol induction dose in morbidly obese patients: A randomized controlled trial comparing the bispectral index and lean body weight scalar

Yamini Subramani, Waleed Riad, Frances Chung, Jean Wong

Propofol dosing based on total body weight (TBW) can lead to overdosing in morbidly obese (MO) patients. Our aim was to determine whether an induction dose of propofol based on a bispectral index (BIS) target is better for achieving loss of consciousness in MO patients than dosing based on lean body weight (LBW). Sixty MO patients with a body mass index (BMI) of ≥ 40 kg·m(-2) were randomized to either BIS- or LBW-based propofol dosing groups. Anesthesia was induced with a propofol infusion of 100 mg·kg(-1)·hr(-1) to an initial target endpoint of a BIS of 50 (BIS group) or until a precalculated dose of 2.6 mg·kg(-1) LBW based on the Janmahasatian equation was administered (LBW group). Induction was assessed using the observer's assessment alertness/sedation scale (OAA/S). If an OAA/S score of 0 was not achieved, infusions continued until it reached 0. The groups were compared for the primary outcome which was the difference in the propofol doses at the initial target endpoint. The median [interquartile range] OAA/S score at the initial target endpoint was lower in the BIS group than in the LBW group (0 [0-0] vs 1 [0-3], respectively; median difference 1, 95% confidence interval [CI] 0 to 3; P = 0.001). The number of patients requiring additional propofol doses was also higher for the LBW group [1 vs 18 patients, respectively; relative risk of requiring additional propofol 18; 95% CI 3 to 126; P = 0.001]. The mean (SD) propofol dose at the target endpoint was significantly lower in the LBW group than in the BIS group [164 (36) mg vs 225 (44) mg, respectively; mean difference 61 mg; 95% CI 41 to 83 mg; P = 0.002]. There was no difference between the two groups, however, regarding the total induction dose of propofol needed for the OAA/S to reach 0 (P = 0.07). The induction dose of propofol based on the BIS index was different from the induction dose based on LBW in MO patients. Patients in the LBW group required additional propofol to achieve an OAA/S of 0.