The analgesic effects of epidural diamorphine and levobupivacaine on established lower limb post-amputation stump pain--a comparative study

Abstract

Background and objectives: Pain is necessary for survival but chronic pain is disabling and causes significant health and economic problems. Chronic stump pain (pain localized in the stump for >3 months) after amputation is a significant problem among amputees (5-10%). The mechanism of this phenomenon is not very clear yet. In this study we attempted to better understand the role of peripheral and central mechanisms in this condition.

Methods: 12 patients with established lower limb post-amputation stump pain were given lumbar epidural diamorhpine 5 mg in 20 ml normal saline (NS) and levobupivacaine 0.5% (20 ml) 1 week apart. Baseline pain was recorded and then analgesic and side effects as well as their onset and duration were also assessed.

Results: Epidural diamorphine was found to relieve the pain of all patients. Its onset was relatively rapid being started within 5-9 min (median = 5.5) by a smooth sensation of warmth involving the lower trunk and legs. Analgesia was complete in 30 min and had a median duration of 20.5 h. Pruritus in 6 patients was the only side effect due to epidural diamorphine. Epidural levobupivacaine, on the other hand, usually relieved the discomfort but failed to do so in 3 patients only despite adequate neural blockade. Its onset of action was slower (10-20 min, median = 11) and duration of effect (median = 12 h) was also shorter than diamorphine. The effects of levobupivacaine were inferior to diamorphine due to the associated motor and sensory paralyses as well as absence of euphoria. Epidural diamorphine provided profound analgesia with normalization of stump sensations and euphoria, probably due to absorption into the spinal cord causing segmental action.

Conclusion: While peripheral mechanisms played a role, central mechanisms involving the spinal cord were more important in the modulation of established stump pain in the evaluated patients.