Naloxone as narcotic antagonist after balanced anaesthesia

Different modes of naloxone administration were studied in 100 patients following N2O-O2-relaxant anaesthesia, where fentanyl was administered for analgesia according to a standardized dose schedule (mean 4.3 microgram/kg/h). After reversal of muscular relaxation, the patients were randomly given naloxone--either 1.0 or 2.5 microgram/kg i.v. or 2.5 or 5.0 microgram/kg i.m., or none (control). Each group consisted of 20 patients. Awakening was fastest after 2.5 microgram/kg i.v. of naloxone (1.8 +/- 0.1 min), the time being significantly shorter (P less than 0.025) than in the control group (2.7 +/- 0.4 min). After 15 min, the minute volume and frequency of respiration were significantly higher (P less than 0.05) in all naloxone groups than in the control group. However, the arterialized venous PCO2 did not show significant differences during the recovery. It is therefore suggested that naloxone reversal may cause an increase in CO2 production. The immediate postoperative pain (score 0-3) was mildest in the control group (1.0 mean) and severest after 2.5 microgram/kg i.v. of naloxone (1.8 mean); the difference was statistically significant (P less than 0.05). The groups receiving 1.0 microgram/kg i.v. and 2.5 microgram/kg i.m. did not differ from each other (1.2 mean). Nausea and vomiting were reported more often after 5.0 microgram/kg im. of naloxone than in other groups. After moderate doses of fentanyl during balanced anaesthesia, routine use of naloxone does not seem to be necessary, but if rapid recovery is essential, 1.0 microgram/kg i.v. or 2.5 microgram/kg i.m. of naloxone may be recommended and these doses do not cause a higher incidence of side effects.