Lumbar epidural morphine in humans and supraspinal analgesia to experimental heat pain

Background Epidural administration of morphine is a common analgesic techni que to manage pain. Morphine spreads from the epidural space to the cerebro spinal fluid and then rostrally, causing side effects mediated by the brain stem. However, data oil the rostral spread of morphine-mediated analgesia are sparse. This study examined the rostral spread of analgesic effects on heat and electrical pain after epidural administration of morphine. Methods: Ln a randomized, double-blinded, placebo-controlled, crossover stu dy, 5 mg morphine or saline placebo were injected into the lumbar epidural space in nine healthy volunteers. Correct needle placement was confirmed wi th fluoroscopy. Analgesia to experimental nociceptive heat and electrical s timuli was measured at lumbar (L4), thoracic (T10), cervical (C2), and trig eminal (V2) levels before and 2, 5, 10, and 24 h after epidural injection. Plasma samples for assaying morphine concentrations were drawn before and a fter each analgesic evaluation, Results: Epidural morphine significantly attenuated experimental heat pain at all dermatomes tested compared with saline placebo. Analgesic effects we re significant at L4 after 2, 5, and 10 h, at T10 after 5, 10, and 24 h, an d at V2 after 10 h. Electrical pain was attenuated at the lumbar and thorac ic but not at the cervical dermatome, Analgesic effects were significant at L4 after 2, 5, and 10 h and at T10 after 5 and 10 h, Morphine plasma conce ntrations were below the detection limit (1 ng/ml) in eight of the nine sub jects 10 h after epidural injection. Conclusions Lumbar epidural injection of morphine attenuated cutaneous heat pain up to the trigeminal dermatome during a 24-h observation period, In a clinical context, this implies that some types of pain may be attenuated u p to the supraspinal level after lumbar epidural administration of morphine .