Alfentanil causes less postoperative nausea and vomiting than equipotent doses of fentanyl or sufentanil in outpatients

Background: The relative potencies of alfentanil, fentanyl, and sufentanil as a risk factor for postoperative nausea and vomiting have not been determ ined. They were compared in a randomized study designed to obtain equipoten t plasma concentrations of these three opioids at the beginning of the reco very period. Methods: The study included 274 patients treated on an outpatient basis. Th e steady state opioid plasma concentration providing a predicted 50% reduct ion of the minimum alveolar concentration of isoflurane was used to determi ne the relative potency of the opioids. The opioids were prepared in equal volumes at concentrations of alfentanil 150 mu g/ml fentanyl 50 mu g/ml and sufentanil 5 mu g/ml and were administered in vol/kg. Anesthesia was induc ed in a blinded fashion with a bolus of the study opioid (0.05 ml/kg) and 4 -6 mg/kg thiopental and was maintained with isoflurane (0.6-1%) in a nitrou s oxide-oxygen mixture with a continuous infusion of the study opioid (0.06 ml.kg(-1).h(-1)). If necessary up to five additional boluses of opioid (0. 02 ml/kg) could be given. This opioid administration protocol was tested by pharmacokinetic simulations. Results: The incidence of postoperative nausea and vomiting was not differe nt in the postanesthesia tare unit, but in the ambulatory surgery unit it w as significantly lower for alfentanil compared with fentanyl and sufentanil (12, 34, and 35%, respectively P < 0.005), Pharmacokinetic modeling showed that the end-anesthesia opioid plasma concentrations were approximately eq uipotent in the three groups. However, modeling does not support that the d ifference between groups in the postoperative period can be explained by a more rapid disappearance of alfentanil from the plasma. Conclusions: Alfentanil, compared with approximately equipotent doses of fe ntanyl and sufentanil, Is associated with a lower incidence of postoperativ e nausea and vomiting in outpatients.