Effect of Thoracic Epidural Bupivacaine on Somatosensory Evoked Potentials after Dermatomal Stimulation

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Abstract
The effect of epidural bupivacaine (9 ml 0.5%) analgesia on early (< 500 msec) somatosensory evoked potentials (SEPs) with electrkal stimulation of the T-10 and L-1 dermatomes was examined in eight patients. Cortical amplitudes decreased only insignificantly after stimulation of both dermatomes, despite the presence of sensory analgesia (pin prick) from T-3.5 ± 0.4 to L-2.9 ± 0.4 (mean ± SEM). Latency of the SEP components remained unchanged and sensory threshold increased only insignificantly during blockade. We conclude that thoracic epidural analgesia with conventional doses of bupivacaine provides only a limited blockade of fast conducting afferent nerve fibers.