Target-controlled remifentanil in combination with propofol for spontaneously breathing day-case patients

Remifentanil is a new potent opioid with a very short duration of action irrespective of duration of infusion. It may have a role in day-case anaesthesia as part of a balanced total intravenous anaesthetic technique with propofol. We examined the respiratory depressant effects of remifentanil in 20 patients undergoing day-case anaesthesia. The target plasma concentration of remifentanil was varied while maintaining a constant target-controlled infusion of 4.5 mu g.ml(-1) propofol. In only 12 patients was satisfactory spontaneous respiration maintained. In these patients the median remifentanil target concentration was 1.6 ng.ml(-1) and was achieved with a median infusion rate of 0.05 mu g.kg(-1).min(-1). The range of target concentrations associated with satisfactory spontaneous respiration was wide and varied over a 4.7-fold range from 0.6 to 2.8 ng.ml(-1).