A comparison of the respiratory effects of oxycodone versus morphine: a randomised, double‐blind, placebo‐controlled investigation*

Abstract

Oxycodone's respiratory profile (particularly the extent of respiratory depression in comparison to morphine) remains to be fully characterised in the peri-operative period. We randomly assigned ASA 1-2 adults for elective surgery under general anaesthesia to receive saline, morphine 0.1 mg.kg⁻¹, or oxycodone 0.05 mg.kg⁻¹, 0.1 mg.kg⁻¹, or 0.2 mg.kg(-1) . Results were obtained from six patients in the saline group, 12 patients in the groups receiving morphine 0.1 mg.kg⁻¹, oxycodone 0.05 mg.kg⁻¹ and 0.1 mg.kg⁻¹, and from 10 patients who received oxycodone 0.2 mg.kg⁻¹. Patients were breathing spontaneously and minute ventilation monitored with a wet wedge spirometer for 30 min. All active groups demonstrated significant respiratory depression compared to saline (p < 0.0001 for all groups). The mean (SD) reduction in minute volume from baseline was 22.6% (10.4%) for the morphine 0.1 group and 53.3% (27.2%), 74.4% (12.9%) and 88.6% (13.5%) for the oxycodone 0.05, 0.1 and 0.2 groups, respectively, with significant dose dependent differences between oxycodone groups (p = 0.0007). The extent and speed of onset of oxycodone induced respiratory depression was dose dependent and greater than an equivalent dose of morphine.