THE NEUROTOXICITY OF INTRATHECALLY ADMINI STERED AGENTS

Spinal anaesthetics can induce histopathologic lesions and regional ha emodynamic alterations in the spinal cord. There are numerous causes o f neurologic lesions, including direct trauma of the spinal cord and n erve roots during puncture or catheter insertion, compromised spinal c ord perfusion and direct neurotoxic effect, Histopathologic lesions ar e localized either in meninges (meningitis or arachnoiditis) or in neu raxis (myelitis or axonal degeneration). Neurotoxicity can result from decrease in neuronal blood supply, elicited by high concentrations of the solutions, long duration exposure to local anaesthetics, and the use of adjuvants. They have been implicated in the occurrence of cauda equina syndrome after continuous spinal anaesthesia using hyperbaric solution of lidocaine and tetracaine given through small diameter cath eters. Selective spinal analgesia is induced by spinal opioids without motor blockade except for meperidine. Complications occurred in patie nts after high doses of morphine, which were related to one of its met abolites, morphine-3-glucuronide. Preservative-free opioid solutions a re to be preferred for spinal anaesthesia. There is no report of neuro toxicity neither in animal studies, nor in humans, using spinal clonid ine. In order to reduce the incidence of neurotoxicity, some safety ru les should be followed. The lowest efficient dose of local anaesthetic s must be given. Incomplete blockade should not necessarily lead to a reinjection. Large volume of hyperbaric lidocaine or repeated injectio ns of such solutions must be avoided as well as preservative-containin g solutions. The administration of new compounds by the spinal route m ust be supported by data of spinal neuropharmacology and the lack of n eurotoxicity must have been previously checked with animal studies.