Alfentanil infusion in the elderly. Prolonged computer-assisted infusion of alfentanil in the elderly surgical patient.

The use of a computer-assisted infusion of alfentanil, combined with 66% nitrous oxide in oxygen, for induction and maintenance of anaesthesia was evaluated in 18 elderly patients. The target alfentanil concentration for induction was varied between 300 and 475 ng/ml, to be achieved in 2 minutes. During maintenance, the alfentanil concentration was increased or decreased according to each patient's responses. Arterial blood samples were taken for measurement of alfentanil concentration. There were high incidences of muscle rigidity, bradycardia and hypotension during induction. Hypotension was dose- and concentration-dependent. Signs of light anaesthesia during maintenance were controlled rapidly by increasing the target plasma concentration. Nine patients required naloxone at the end of surgery. Ventilatory depression recurred in three of these. The use of published alfentanil pharmacokinetic data from elderly patients to predict plasma concentrations during prolonged infusion resulted in significant prediction errors, notably in the higher concentration range.