Quantitative sensory examination of epidural anaesthesia and analgesia in man: combination of morphine and bupivacaine

Abstract

The effect of epidural administration of a combination of low-dose morphine (2 mg) and bupivacaine (25 mg) on somatosensory and motor functions was examined in 13 healthy volunteers. The study design was a double-blind 4-way cross-over in which combined treatment was compared with either drug used alone or placebo. Every 2nd hour for 10 h effects on nociceptive and non-nociceptive somatosensory functions were quantified with 12 psychophysical measures. In addition knee extension strength, reaction time and skin temperature were examined. Epidural bupivacaine had hypoalgesic effect in all nociceptive tests, whereas epidural morphine only demonstrated hypoalgesic properties in nociceptive test with prolonged stimuli. In comparison with bupivacaine alone the combination treatment had a lesser peak effect but a more prolonged hypoalgesic action. In comparison with morphine alone the combination treatment induced a faster onset and demonstrated a modest increase in hypoalgesic effect in a subset of the test, even beyond the duration of bupivacaine when administered alone. Motor function was not attenuated by any of the treatments. Mechanisms of interaction between morphine and bupivacaine as well as their possible clinical implications are discussed.