Lean Body Weight Scalar for the Anesthetic Induction Dose of Propofol in Morbidly Obese Subjects

BACKGROUND: The unique anesthetic risks associated with the morbidly obese (MO) population have been documented. Pharmacologic management of these patients may be altered because of the physiologic and anthropometric changes associated with obesity. Unfortunately, studies examining the effects of extreme obesity on the pharmacology of anesthetics have been sparse. Although propofol is the induction drug most frequently used in these patients, the appropriate induction dosing scalar for propofol remains controversial in MO subjects. Therefore, we compared different weight-based scalars for dosing propofol for anesthetic induction in MO subjects. METHODS: Sixty MO subjects (body mass index >40 kg/m(2)) were randomized to receive a propofol infusion (100 mg . kg(-1) . h(-1)) for induction of anesthesia based on total body weight (TBW) or lean body weight (LBW). Thirty control subjects (body mass index <= 25 kg/m(2)) received a propofol infusion (100 mg . kg(-1) . h(-1)) based on TBW. Syringe drop was used as the marker for loss of consciousness (LOC), at which point the propofol infusion was stopped. The propofol dose required for syringe drop and time to LOC were recorded. RESULTS: Total propofol dose (mg/kg) required for syringe drop and time to LOC were similar between control subjects and MO subjects given propofol based on LBW. MO subjects receiving a propofol infusion based on TBW had a significantly larger propofol dose and significantly shorter time to LOC. There was a strong relationship between LBW and total propofol dose received in all 3 groups. CONCLUSION: LBW is a more appropriate weight-based scalar for propofol infusion for induction of general anesthesia in MO subjects. (Anesth Analg 2011;113:57-62)