Comparison of near-infrared spectroscopy and somatosensory evoked potentials for the detection of cerebral ischemia during carotid endarterectomy

Background and Purpose-We sought to assess the clinical value of regional cerebral saturation (rSO(2)) obtained by means of the cerebral oximeter INVOS 3100A (Somanetics) in comparison to monitoring of somatosensory evoked potentials (SEP) for the reliable detection of severe cerebral ischemia requiring shunt placement in the individual patient undergoing carotid surgery under general anesthesia. Methods-In 317 patients undergoing reconstructive surgery on the internal carotid artery, simultaneous recordings of SEP and rSO(2) were obtained throughout the operation. Results-All 287 patients with preserved cortical SEP remained neurologically intact. Shunt placement was performed in 27 patients (9%) after flattening of cortical SEP during cross-clamping of the internal carotid artery. A stable rSO(2) value just before cross-clamping and the lowest value after cross-clamping were registered, and the decrease was calculated. A statistically significant (P<0.01) decrease of rSO(2) after cross-clamping could be found in patients without (64.9+/-8.3% to 60.9+/-9.9%) as well as in patients with consecutive loss of cortical SEP (65.8+/-9.1% to 56.1+/-13.4%). The difference of the decrease of rSO(2) in both groups was highly significant (6.9%+/-9.0% versus 15.6+/-14.0%; P<0.001). However, substantial interindividual variability of rSO(2) and derived change of rSO(2) did not allow the definition of a threshold value indicating need of shunt placement. Conclusions-The reliability of SEP for the detection of clamp-related hypoperfusion has been reaffirmed. As long as rSO(2) threshold values indicating critical cerebral ischemia are not defined, therapeutic interventions based on monitoring with the cerebral oximeter INVOS 3100A are not justified.