Ventilatory effects of pre- and postoperative diamorphine. A comparison of extradural with intramuscular administration

Abstract

Twenty-two patients were studied before and after major abdominal vascular surgery to determine the effect on ventilation of 5 mg diamorphine given either extradurally or intramuscularly. Diamorphine depressed ventilation maximally at 30 minutes when given by either route. Before operation resting ventilation was reduced by 33% after extradural and 17% after intramuscular diamorphine; PaCO2 increased by an average of 0.5 kPa (either route); ventilation at 7.3 kPa PaCO2 was reduced 40% after extradural and 33% after intramuscular diamorphine. After operation the effect of diamorphine on ventilation was qualitatively similar but resting baseline ventilation was increased from 9.4 to 10.9 litres/minute. The highest individual PaCO2 values were found during the pre-operative study: 6.5 kPa after extradural diamorphine, 6.4 kPa after intramuscular diamorphine. Pain relief was unsatisfactory after intramuscular diamorphine. Four out of six patients requested further analgesia by 3 hours after administration. No patient who received extradural diamorphine required further analgesia for at least 6 hours.