A comparison of two techniques for induction of anaesthesia with target-controlled infusion of propofol

Induction of anaesthesia with target-controlled infusion of propofol may be achieved by stepwise increases in effect-site concentration until the patient loses consciousness (titration method), or by setting a high effect-site concentration target and observing the calculated effect-site concentration at loss of consciousness (standard method). When the estimated effect-site concentration at loss of consciousness is accurate, the difference between effect-site concentration at loss of consciousness and at recovery of consciousness should be small. This prospective, randomised, controlled trial was designed to compare this difference (effect-site concentration at loss of consciousness - effect-site concentration at recovery of consciousness) associated with the two techniques. Sixty-seven healthy patients undergoing elective hemithyroidectomy were recruited. Induction of anaesthesia was achieved using effect-site target-controlled infusion with the modified Marsh model and k_e0 of 1.2 min^-1 . The median (IQR [range]) difference between effect-site concentration at loss of consciousness and recovery of consciousness was significantly lower in patients in the titration group at 1.2 (0.8-1.5 [0.1-2.9]) μg.ml^-1 compared with the standard group 2.1 (1.9-2.6 [0.2-3.6] μg.ml^-1 ; p < 0.0001). There was a positive correlation between effect-site concentration at loss of, and recovery of, consciousness (R = 0.41, p = 0.016) in the titration group, which was not seen in the standard group (R = -0.15, p = 0.44). In conclusion, using the modified Marsh pharmacokinetic model, the titration method for target-controlled infusion propofol at induction of anaesthesia allows closer matching of propofol concentration to depth of anaesthesia than the standard method.