Background: For induction of anaesthesia, drugs such as propofol are commonly administered according to a per weight basis. However, drugs are primarily distributed to the fat-free mass. This study was undertaken to determine the relationship between propofol requirement for induction and body mass determined by bioimpedance analysis (BIA) or by body mass index (BMI).
Methods: Twenty-one ASA 1 female patients scheduled for gynaecologic surgery received propofol for induction at 133 mg.min-1. Stepwise regression analysis was used to describe the relationships between propofol requirement for loss of consciousness and age, body weight, and lean body mass measured by BIA and BMI (independent variables).
Results: Loss of consciousness was obtained with a propofol dose (Mean (SEM)) of 2.17 +/- 0.10 mg.kg-1. Stepwise analysis showed that propofol requirement (total dose) was not proportional to weight or age but related to lean body mass as determined by BIA and to body mass index (r2 = 0.447; global P- value < 0.007). BMI was the only regressor variable when the propofol dose was expressed in mg.kg-1 (r2 = 0.661; P < 0.001).
Conclusions: Our results indicate that propofol requirements for induction are proportional to the lean body mass rather than total body weight.