Studies on fentanyl-supplemented anaesthesia: effect on naloxone on the circulation and respiration.

Ninety-nine unselected patients were given a standardized general anaesthetic with fentanyl 1.5 microgram . kg-1 every 30 minutes and were randomly divided into three equal Groups: Group I patients received naloxone 0.1 mg. Group II naloxone 0.2 mg, and Group III naloxone 0.4 mg, at the end of operation and after the reversal of neuromuscular blockade. After administration of naloxone systolic blood pressure increased by 4, 8 and 7 per cent and mean arterial blood pressure increased by 3, 8 and 8 per cent in Groups I, II and III respectively; heart rate increased by 4, 11 and 8 per cent and rate-pressure product increased by 7, 18 and 15 per cent in Groups I, II and III respectively. Tidal volume increased by 97, 101 and 95 per cent and minute volume increased by 122, 164 and 143 per cent in Groups I, II and III respectively after naloxone. Forty-nine per cent of patients had a tidal volume of less than 5 ml . kg-1 or a minute volume of less than 50 ml . kg-1 before administration of naloxone; after naloxone three patients in Group I (naloxone 0.1 mg) had a tidal volume of less than 5 ml . kg-1 and no patient had a respiratory minute volume of less than 50 ml . kg-1. It is concluded that under the conditions of this study naloxone 0.1 mg is adequate to reverse the respiratory depressant effect of fentanyl in the majority of cases.