Comparison of computer-controlled administration of propofol with two manually controlled infusion techniques

Ninety women were studied in order to compare dose requirements and quality of anaesthesia between target-controlled infusion and two manually controlled infusion schemes for propofol administration: group I received target-controlled infusion for induction (4 μg.ml⁻¹ target blood concentration, increased by 2 μg.ml⁻¹ after 3 min if consciousness not lost), groups II and III received an induction bolus of propofol at infusion rates of 1200 or 600 ml.h⁻¹, respectively, until loss of consciousness. Anaesthesia was maintained with propofol target-controlled infusion in group I or by constant rate infusion in the other two groups. Computer simulations were used to calculate blood and effect-site propofol concentrations. Mean induction times (SD) were 78 (65) s in group I versus 51 (10) s and 62 (12) s in groups II and III, respectively (p < 0.05 between groups II and III). Mean induction doses were: 1.31 (0.44), 2.74 (0.56) and 1.77 (0.43) mg.kg⁻¹ and mean maintenance doses were 13.4 (3.55), 9.32 (1.71) and 9.97 (1.53) mg.kg⁻¹.h⁻¹ in groups I, II and III, respectively (p < 0.05 between all groups). There was a lower incidence of apnoea in group I than in groups II and III. There were no significant differences between the groups in other objective parameters of anaesthetic quality studied. Computer simulations showed an 'overshoot' in propofol blood and effect-site concentration with manual induction and significantly higher maintenance levels with target-controlled infusion.