Monitoring of median nerve somatosensory evoked potentials in carotid surgery

The purpose of this study was to compare median somatosensory evoked potent ials (SEP) in patients undergoing carotid endarterectomy (CEA) with routine shunting and nonshunting (excluding the option of selective shunting) and to evaluate the significance of a decrease in the amplitude of the cortical ly generated waveforms of the SEP and/or an increase in the central conduct ion time (CCT) on the one hand, and that of a loss of the cortical SEP, on the other. Somatosensory evoked potentials were recorded in 32 patients bef ore, during, and after CEA with routine shunting or nonshunting. The N13 an d N20 latency, the CCT, and the N20/P25 amplitude were evaluated. In additi on, a meta-analysis of 15 previous studies was performed comprising a total of 3,136 patients. The intraoperative cortical SEP showed no differences b etween shunted and nonshunted patients, apart from the preclamping value of the N20/P25 amplitude which was lower in the nonshunted subjects. The numb er of patients with decreased and/or delayed cortical SEP (findings frequen tly used as criterion for selective shunting) was similar in the two study groups. A loss of the cortical SEP occurred in one patient operated on with out an indwelling shunt. None of these patients had a new neurologic defici t after surgery. In the meta-analysis, the positive predictive value of dec reased and/or delayed cortical SEP was extremely poor, that of absent corti cal SEP was poor to moderate and the prevalence of new neurologic deficits was similar in patients undergoing CEA with routine shunting-nonshunting an d those with selective shunting-nonshunting. Our study suggests that decrea sed and/or delayed cortical SEP are unreliable predictors of the neurologic al outcome of CEA patients and consequently an unsuitable criterion for sel ective shunting. The meta-analysis confirms this finding and shows that the neurologic outcome is not improved by using an indwelling shunt selectivel y based on SEP monitoring.