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Fixed-rate alfentanil infusions for surgery of variable duration.

The continuous infusion of alfentanil with a modified Fresenius-injectomat infusion pump was studied in 27 patients undergoing orthopaedic operations of variable length. Patients were premedicated with diazepam 10 mg orally. Anaesthesia was induced with thiopentone, vecuronium and an anfentanil loading dose delivered by the infusion pump at a rate of 10 micrograms kg-1 min-1 for 10 min. The patients' lungs were ventilated with 66% N2O in O2. After 10 min the maintenance infusion rate of alfentanil of 1 microgram kg-1 min-1 was begun. An incremental dose of 15 micrograms kg-1 of alfentanil was administered if inadequate anaesthesia was present. Ten to twenty minutes before the completion of surgery, the alfentanil infusion was stopped. At the end of surgery N2O was discontinued. This moment was defined as the end of anaesthesia. The mean duration of anaesthesia was 139.3 +/- 9.4 min (SEM). The time between the end of anaesthesia and eye opening and the time to giving correct answers to five questions after eye opening were, respectively, 3.1 +/- 0.6 min and 3.5 +/- 0.9 min. Recovery was uneventful in all but one patient, who had ventilatory depression that responded to naloxone. All patients were satisfied with their anaesthesia and recovery. The use of a 10-min, 10 micrograms kg-1 min-1 loading infusion, then a maintenance infusion of 1 microgram kg-1 min-1 delivered by a modified Fresenius-injectomat infusion pump may be the first step in simplifying the continuous infusion of alfentanil.