Alfentanil or fentanyl for anaesthetic procedures of two hours duration? A double-blind study

Eighty women undergoing surgery of at least 2-h duration were randomly allocated to receive either alfentanil or fentanyl to supplement a diazepam nitrous oxide/oxygen anaesthetic. Anaesthesia was induced with fentanyl 0.2 mg and diazepam 10-20 mg and continued with nitrous oxide/oxygen. Analgesia was provided by injection of the narcotic using unlabelled ampoules that contained either alfentanil 0.5 mg ml-1 or fentanyl 0.05 mg ml-1. Apart from a marginally higher heart rate when alfentanil was used, there was no significant difference between groups at any time during the operation. Patients woke 2.7 +/- 3.1 min following discontinuation of nitrous oxide and were extubated after 10.3 +/- 7.6 min (alfentanil) and 17.3 +/- 19.0 min (fentanyl) (P = 0.1). However, following alfentanil significantly more patients could be extubated within 20 min to 30 min after completion of the operation (P less than 0.01). The last top-up dose of alfentanil had to be given nearer the end of the operation than the last dose of fentanyl (P less than 0.01). Patients receiving alfentanil needed significantly more (P less than 0.01) post-operative analgesia.