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The role of somatosensory evoked potentials in detecting cerebral ischaemia during carotid endarterectomy: An assessment of its validity under regional anaesthesia

Background and objective The generation of shunt criteria by somatosensory evoked potentials is controversial. This study was designed to validate somatosensory evoked potentials' tracings and their derived shunt criteria compared with clinical‐neurological examination. Methods We prospectively studied the somatosensory evoked potentials' tracing in 102 patients who underwent carotid endarterectomy under cervical plexus blockade, comparing different somatosensory evoked potentials' derived thresholds of impaired cerebral blood flow with the neurological examination. Results The 50% reduction of the primary cortical response to median nerve stimulation as threshold of critical cerebral blood flow showed a sensitivity of 87% and a specificity of 66%. In case of total collapse of primary cortical response, we observed a sensitivity of 85% and a specificity of 89%. Concerning the prolongation of central conduction time between the spinal response at N13 and the cortical response at N20/P25 as critical threshold of impaired cerebral blood flow, the sensitivity was 87% and specificity 40%. The need‐to‐shunt index with its threshold at >0.5 showed a sensitivity of 85% and a specificity of 88%. Conclusion Compared to other studies, we have shown a much lower sensitivity and specificity of somatosensory evoked potentials in detecting critical cerebral perfusion; thus its use remains controversial and has to be assessed in further investigations.