A comparison of the effects of intrathecal fentanyl and lidocaine on established postamputation stump pain

Eight patients with established lower limb postamputation stump pain were given lumbar intrathecal fentanyl 25 μg and lidocaine 70 mg 2 weeks apart in an attempt to better understand the role of peripheral and central mechanisms in this condition. Baseline pain was recorded and then analgetic and side effects and their duration were assessed. Three self-administered questionnaires with appropriate psychometric proprieties were given to the patients. Intrathecal fentanyl always abolished the pain. Its onset was rapid being heralded within 1–2.5 min by a pleasant sensation of warmth involving the lower trunk and legs. Analgesia was complete by 5–10 min and had a median duration of 8 h. The patients had a sense of well being and were unable to elicit discomfort by pain aggravating maneuvers. Normal motor and sensory functions were retained. Pruritus was the only adverse effect unique to intrathecal fentanyl. Intrathecal lidocaine usually relieved the discomfort but was unable to abolish it in 3 of 8 patients despite adequate neural blockade. Its onset of action was slower and duration of effect shorter than fentanyl. Intrathecal fentanyl provided profound analgesia associated with normalization of stump sensations and euphoria, probably due to a segmental spinal action. The effects of lidocaine were inferior to fentanyl due to the associated motor and sensory paralyses as well as the absence of euphoria. This study suggests that, while peripheral mechanisms played a role, central mechanisms involving the spinal cord were more important in the modulation of established stump pain in the 8 subjects evaluated.