Improvement of intraoperative somatosensory evoked potentials by etomidate.

Use of somatosensory evoked potentials (SSEPs) for monitoring of the nervous system during corrective surgery on the spine has stimulated interest in the effect of anesthetics on SSEPs. Inhalation anesthetics have generally demonstrated a dose-dependent depression of amplitude and increase in latency, with intravenous agents generally showing lesser depression of amplitude and latency. This suggested to many that a narcotic-based anesthetic technique may be superior when monitoring patients with lowamplitude evoked responses. A particular monitoring challenge occurs in patients in whom preexisting neural abnormalities may make monitoring difficult. These patients may be at greater risk for neural complications, making monitoring most important at a time when it is also most difficult (1). As with the following case, the intraoperative evoked responses may be too poor to be reliably monitored. An anesthetic that would increase the amplitude of evoked responses might make the response usable for monitoring. Etomidate may be such an agent. As shown in several studies ( 2 4 , etomidate increases the amplitude of cortically derived median nerve SSEPs. We now report a case in which the introduction of etomidate during a narcotic anesthetic improved SSEPs responses from posterior tibial nerve stimulation and allowed the patient's neural function to be monitored when it would otherwise have been considered unreliable.