High spinal anesthesia does not depress central nervous system function as measured by central conduction time and...

Short-latency somatosensory evoked potentials (SSEPs) in response to median nerve stimulation were recorded from the neck and the scalp before and during diagnostic high spinal anesthesia (touch T3, pinprick C8) in six patients with chronic pain. The central conduction time--the time difference between the neck-recorded N13 and the scalp-recorded N20--and the amplitudes of the SSEPs did not change in a statistically significant way during high spinal anesthesia. However, latencies of the neck-recorded N13 and the scalp-recorded N20 and P25 increased slightly. This may have been due to a local anesthetic effect on those spinal roots of the median nerve in which segmental pinprick analgesia occurred. Because high spinal anesthesia did not depress central nervous function, as measured by central conduction time, and SSEP amplitudes, it is concluded that scalp-recorded SSEPs during high spinal anesthesia measure the effects of local anesthetics in the cerebrospinal fluid on neuronal pathways outside the brain.