Published in Br J Anaesth. 2015 Apr;114(4):605-14
Authors: Liu N et al
We used an automated bispectral index (BIS)-guided dual-loop controller to determine propofol and remifentanil requirements during general anaesthesia in obese and lean surgical patients.
Obese patients, BMI>35 kg m(-2), and lean patients (<25 kg m(-2)) having laparoscopic procedures were prospectively evaluated in this multicentre single-blind study. The automated controller targeted BIS between 40 and 60 by adjusting propofol and remifentanil administration. Propofol and remifentanil consumptions were calculated using both total body weight (TBW) and ideal body weight (IBW). Results are expressed as medians (inter-quartile range).
Thirty obese [BMI=43 (40-49) kg m(-2)] and 29 lean [BMI=23 (21-25) kg m(-2)] patients completed the study. BIS was between 40 and 60 during 84 (69-91)% vs 85 (78-92)% of the anaesthetic time, P=0.46. The amount of propofol given during induction [1.2 (1.1-1.6) vs 1.3 (1.0-1.7) mg kg(-1), P=0.47] and maintenance [5.2 (4.1-6) vs 5.3 (4.7-6.4) mg kg(-1) h(-1), P=0.39] calculated using TBW was similar between the two groups. The dual-loop controller delivered half as much remifentanil to the obese patients during induction [1.0 (0.8-1.6) vs 2.2 (1.5-2.7) µg kg(-1), P<0.001] and maintenance [0.12 (0.07-0.16) vs 0.25 (0.17-0.29) µg kg(-1) min(-1), P<0.001] calculated using TBW. But when remifentanil consumption was calculated using IBW, the amounts were similar during induction at 2.2 (1.6-3.5) vs 2.0 (1.6-3.0) µg kg(-1) IBW, P=0.48, and during maintenance at 0.26 (0.16-0.34) vs 0.27 (0.18-0.33 ) µg kg(-1) min(-1), P=0.50.
The amount of propofol-remifentanil administered by the controller is consistent with current knowledge, propofol is best dosed using TBW whereas remifentanil is best dosed using IBW.