[Somatosensory evoked potentials in obliterating interventions of the carotid bifurcation]

A prospective study was undertaken to determine the prognostic value of somatosensory evoked potentials during carotid artery surgery in patients where an intraluminal shunt was not used. During a three-year period 167 patients underwent 193 consecutive carotid endarterectomies under general anaesthesia. The somatosensory evoked potential after median nerve stimulation including calculation of central conduction time was used to assess cerebral function intraoperatively. Early postoperative neurologic morbidity was 3.6%, mortality 0.6%. Evoked potential changes in these patients were uniform and consisted of an increase in central conduction time of more than 20% from control (anaesthetic baseline), a decrease of the amplitude of the primary cortical response exceeding 50% and a loss of middle latency components. In subsequent recordings complete loss of the entire cortical evoked potential was observed in 5 of 7 patients. Sensitivity of CCT prolongation was 100%, specificity 89% (18 false positives). For amplitude reduction sensitivity was 86% (1 false negative), specificity 96% (7 false positives). For loss of the entire cortical response sensitivity was 71% (2 false negatives), specificity 99% (2 false positives). The above mentioned parameters correlated with postoperative neurologic state (Chi-square, p = 0.0001). Since the effects of potentially confounding variables (anaesthetics, temperature) are well known, the somatosensory evoked response, especially central conduction time, can be used as a reliable guide for brain supporting procedures.