Neurological toxicity of the subarachnoid infusion of bupivacaine, lignocaine or 2-chloroprocaine in the rat

Neurotoxicity after subarachnoid infusion of bupivacaine, lignocaine and 2-chloroprocaine was studied in a chronic rat model. Hartmann's solution 100 μl h^-1 was infused as a control, and 0.5% bupivacaine, 1.5% lignocaine and 2.0% 2-chloroprocaine were infused at 100 μl h^-1 for 3, 6 or 24 h, to five rats in each group. No residual paralysis occurred in the control group, but 27 of 45 rats (60%) which received an infusion of local anaesthetic had residual paralysis lasting until sacrifice at 7 days. The incidence of paralysis was dependent on the duration of exposure to the local anaesthetic, but there were no significant differences in incidence between any of the local anaesthetics tested. Abnormal histology, in the form of neuronal vacuolation, was not a sensitive index, being present in control rats, but more intense in those receiving lignocaine and 2-chloroprocaine than in those given bupivacaine; no correlation with clinical findings could be established. The neurotoxic effects of each local anaesthetic tested as a continuous intrathecal infusion were dose related in the rat, which maybe a useful model for screening other local anaesthetics.