Prospective randomised comparison of Marsh and Schnider pharmacokinetic models for propofol during induction of anaesthesia in elective cardiac surgery

Abstract

Haemodynamic stability during induction is a cornerstone of cardiac anaesthesia. The evaluation of pharmacokinetic models for propofol during induction is lacking. To compare haemodynamics during cardiac anaesthesia induction with two pharmacokinetic models. Randomised controlled trial. Department of Cardiothoracic Surgery, São João Hospital; July to December 2010. Ninety consecutive elective adult cardiac surgical patients. Random assignment to effect-site target-controlled infusion by Marsh (n = 45) or Schnider (n = 45) pharmacokinetic models with an equilibration constant of 1.2 min(-1) adapted to Marsh's model. Invasive blood pressure measurements, propofol dose, and bispectral index (BIS) were recorded. After an initial target concentration of 1.5 μg ml(-1), concentrations were upward-titrated in 0.5 μg ml(-1) increments until the BIS was <50. No differences were observed between Marsh and Schnider models in required propofol dose (0.99 ± 0.26 vs. 0.93 ± 0.31 mg kg(-1), P = 0.322), decrease in mean blood pressure (25 ± 13 vs. 22 ± 14%, P = 0.192) or the need for vasopressors (20 vs. 24%, P = 0.800), but the use of the Marsh model resulted in a lower predicted effect-site concentration (2.3 ± 0.4 vs. 2.7 ± 0.6 μg ml(-1), P = 0.006) and shorter time to induction (296 ± 59 vs. 338 ± 87 s, P = 0.024). There was a greater decrease in mean blood pressure in older patients (>60 years; 29 ± 10 vs. 22 ± 11%, P = 0.004) irrespective of model, but obese (BMI ≥30 kg m(-2)) and nonobese patients did not differ. Decrease in mean blood pressure. In effect-site targeting with a 1.2 min(-1) equilibration constant, Marsh's model is comparable to Schnider's during induction of anaesthesia.