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

Summary 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.