The Addition of 7.5% Glucose Does Not Alter the Neurotoxicity of 5% Lidocaine Administered Intrathecally in the Rat

Abstract

Recent reports of major and minor neurologic sequelae after spinal anesthesia have generated concern regarding the safety of some currently used intrathecal agents. The role of glucose, if any, in neurotoxic injury associated with spinal anesthesia is not known. The current experiments sought to determine whether the presence of 7.5% glucose alters the neurotoxicity of intrathecally administered 5% lidocaine. Two experiments were performed. First, 48 rats were implanted with an intrathecal catheter and randomly divided into eight equal groups. Each animal received a single intrathecal infusion of 5% lidocaine (groups P1-P4) or 5% lidocaine with 7.5% glucose (G1-G4) for 0.5, 1, 2, or 4 h at a rate of 1 microliter/min. Sensory function was assessed using the tail-flick test; a deficit was defined as a complete lack of response to the heat stimulus at the proximal, mid or distal portion of the tail persisting 4 days after the infusion. In the second experiment, 60 rats were randomly divided into two groups to receive a 1-h intrathecal infusion of 5% lidocaine or 5% lidocaine with 7.5% glucose. Animals were evaluated for increase in the latency of the tail-flick reflex 4 days after infusion. In the first experiment, the two lidocaine solutions produced similar dose-dependent loss of sensory function. In the second experiment, the two solutions induced similar alterations in tail-flick latency. The presence of 7.5% glucose does not affect the potential of intrathecally administered 5% lidocaine to induce sensory impairment. These findings provide further support for the hypothesis that recent injuries after spinal anesthesia resulted from a direct neurotoxic effect of the local anesthetic.