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Web End = Can J Anesth/J Can Anesth (2017) 64:456460
DOI 10.1007/s12630-017-0854-8
http://crossmark.crossref.org/dialog/?doi=10.1007/s12630-017-0854-8&domain=pdf
Web End = EDITORIALS
Propofol induction: normalizing the dose in morbidly obese patients
John H. P. Friesen, MD
Received: 11 January 2017 / Revised: 14 February 2017 / Accepted: 21 February 2017 / Published online: 3 March 2017 Canadian Anesthesiologists Society 2017
The estimation of appropriate induction doses for obese patients remains controversial but is of considerable importance. Too low a dose risks awareness and sympathetic response and too high a dose risks hypotension and cardiovascular instability. The study by Subramani et al. in this issue of the Journal1 reports induction doses of propofol that are clinically relevant for morbidly obese patients. Propofol was infused at a rate of 100 mg kg-1 hr-1 lean
body weight (LBW) until a target criterion was met. The target in the LBW group was a total dose of 2.6 mg kg-1 LBW, and
the target in the bispectral index (BIS) group was a decrease in the BIS score to 50. When the target for each group was reached, adequacy of induction was assessed every 30 sec until no response was observed to trapezius squeeze. In the LBW group, 18 of 30 patients were still responsive after the initial dose of 2.6 mg kg-1 LBW. In the BIS group, all but one
of 30 patients were unresponsive at the target BIS of 50, which corresponded to a mean value of 3.83 mg kg-1 LBW. Under
the conditions of this study, 2.6 mg kg-1 LBW of propofol
was not adequate for 60% of the patients, and 3.83 mg kg-1
LBW of propofol was enough for all but one patient.
Lean body weight is total body weight (TBW) minus the fat mass. It can be measured using dual-energy x-ray absorptiometry or bioelectrical impedance analysis, but in practice, it is usually estimated using a formula published by Janmahasatian2 that expresses LBW as a function of TBW and the body mass index (BMI):
LBW (kg) for males = 9,720 TBW/(6,680 ? 216 BMI)
LBW (kg) for females = 9,720 TBW/(8,780 ? 244 BMI).
Lean body weight has been recommended for use as a weight scalar when calculating estimated induction doses for morbidly obese patients. This can be justied on...