Optimal propofol-alfentanil combinations for supplementing nitrous oxide for outpatient surgery

Background The combination of propofol and alfentanil with nitrous oxide pr ovides balanced anesthesia with rapid recovery and minimal emetic side effe cts. The object of this study was to compare recovery parameters at varying proportions of propofol and alfentanil, and to determine the dosing rate a nd plasma concentration of propofol necessary to supplement nitrous oxide i n the presence of varying concentrations of alfentanil. Methods: Forty-eight patients were anesthetized with nitrous oxide, targete d manual infusions of alfentanil (target plasma concentrations of 0, 50, 10 0, and 150 ng/ml), and propofol at rates that were varied up or down by 25% depending on the response (movement/no movement) of the preceding patient (at the same alfentanil target concentrations) to ulnar-nerve stimulation. The minimum concentrations of propofol and alfentanil required to prevent m ovement in 50% of patients (EC50) was determined by logistic regression. Sp eed of emergence and recovery of cognitive function, time to discharge, and incidence of side effects were compared for four different combinations of propofol and alfentanil with nitrous oxide. Results: The EC50 for propofol alone with nitrous oxide was 6.1 mu g/ml. Al fentanil, at concentrations of 41 +/- 17 (SD), 113 +/- 54, and 130 +/- 61 n g/ml, reduced the EC50 of propofol to 3.3, 2.3, and 2.2 mu g/ml, respective ly, and decreased emergence time (eye opening) to 8.1, 4.9, and 3.4 min, co mpared with 24.3 min for propofol alone. Side effects did not differ betwee n groups. Conclusions: The authors conclude that there is a synergistic effect betwee n propofol and alfentanil, and that combining alfentanil with propofol is a ssociated with faster early recovery.