Comparison of Fat-Free Mass and Ideal Body Weight Scalar for Anesthetic Induction Dose of Propofol in Patients with Morbid Obesity: A Double-Blind, Randomized Clinical Trial.

Background: Obesity is a growing problem worldwide and can affect both the pharmacodynamics and pharmacokinetics of various drugs, including anesthetics, resulting in the under-or overdosing of certain drugs. There is no consensus on the ideal dosing regimen for obese populations.

Objectives: In this study, 2 weight-based dosing of propofol used for induction of anesthesia were compared in terms of the onset of action time, adequacy of anesthesia, and effects on hemodynamic indices (eg, heart rate [HR] and blood pressure).

Methods: In this randomized, double-blind clinical trial, 40 patients with morbid obesity (MO) scheduled for bariatric surgery with body mass index (BMI) > 35, age 18 - 59 years, American Society of Anesthesiologists physical status (ASA-PS) II and III were randomly divided into 2 groups, using block randomization method, to receive 2 mg/kg of propofol for induction of anesthesia based on either fat-free mass (FFM) group or ideal body weight (IBW) group. The primary outcome was the time duration to reach the bispectral index (BIS) ≤ 60. Time to the disappearance of eyelash reflex, signs of inadequate anesthesia (ie, BIS > 60, straining during intubation, or eye-opening), requirements for additional doses, and hemodynamic indices (including HR and mean arterial pressure [MAP]) were also compared.

Results: The mean time to reach BIS ≤ 60 was 134.1 s in the FFM group and 148.7 s in the IBW group. This difference was not statistically significant (P = 0.334). The time of disappearance of eyelash reflex was also not significantly different between the study groups (P = 0.814). However, 2 patients in the FFM group and 8 patients in the IBW group showed signs of inadequate anesthesia and required additional doses. This difference was statistically significant (P = 0.032). Hemodynamic variables, before and 2 min after propofol induction dose administration were comparable between the study groups (P = 0.520, P = 0.327, P = 0.847, P = 0.516 for pre-intervention MAP, post-intervention MAP, pre-intervention HR, and post-intervention HR, respectively).

Conclusions: Propofol dosing, based on FFM and IBW, for induction of anesthesia, provides comparable onset time of action and hemodynamic effects; however, in terms of the adequacy of anesthesia, the dosing based on FFM is more favorable compared to the dosing based on IBW.