The effect of adding two target-controlled concentrations (1-3 ng mL -1 ) of remifentanil on MAC BAR of desflurane.

BACKGROUND AND OBJECTIVES: The aim of this prospective, randomized, double-blind study was to determine the effects of adding two different target-controlled concentrations of remifentanil (1 and 3 ng mL(-1)) on the desflurane requirement for blunting sympathetic responses after surgical incision (minimum anaesthetic concentration (MAC(BAR)).

METHODS: 67 patients, aged 20-50 yr, ASA I, undergoing general anaesthesia for elective abdominal surgery were enrolled and randomly allocated to receive no remifentanil infusion (n = 21) or a target-controlled effect-site concentration of 1 ng mL(-1) (n = 24) or 3 ng mL(-1) remifentanil (n = 22). All patients were anaesthetized with propofol, cisatracurium and desflurane with a mixture of 60% nitrous oxide in oxygen. Sympathetic responses to surgical incision were determined after a 20-min period of stable end-tidal desflurane and target-controlled remifentanil concentrations. Predetermined end-tidal desflurane concentrations and the MAC(BAR) for each group were determined using an up-and-down sequential-allocation technique.

RESULTS: The MAC(BAR) of desflurane was higher in the group receiving no remifentanil (6.25% [95% confidence interval: 5.9-6.5%]) as compared with patients of the groups receiving 1 ng mL(-1) (2.7% [2.6-2.8%]; P < 0.001) and 3 ng mL(-1) remifentanil (2% [1.9-2.2%]; P < 0.01). When considering a MAC value in this age population and the contribution of 60% nitrous oxide (0.55 MAC), the combined MAC(BAR) values, expressed as multiples of the MAC, were 1.9, 0.8 and 0.6 MAC, in the three groups, respectively.

CONCLUSION: A target-controlled concentration of 1 ng mL(-1) remifentanil results in a 57% decrease in the MAC(BAR) of desflurane combined with 60% nitrous oxide. Increasing the target concentration of remifentanil to 3 ng mL(-1) produces a further 26% decrease in the MAC(BAR) values of desflurane.