[Lung compliance in man is impaired by the rapid injection of alfentanyl]

To demonstrate opioid-induced muscular rigidity, compliance was measured in patients after induction of anaesthesia with etomidate (0.3 mg/kg) and N2O/O2 (2:1) ventilation. Alfentanil was given subsequently to two groups of patients: either as a bolus injection (n = 15) over 3 s, or as a slow injection (n = 15) over 30 s. Significant reduction of compliance (max. 30%) was observed after rapid injection in the following 4 min. This effect was promptly reversed by succinylcholine (25 mg i.v.). The slow injection of the opioid over 30 s, was followed by a small insignificant reduction in compliance. Alfentanil is increasingly used for short-term anaesthesia where no muscle relaxants are administered. Thus slow injection of the opioid is advised in order not to impair adequate ventilation.