Use of Cerebral Oximeters during Carotid Endarterectomy Is Evaluated. Samra et al.(page 964)
Samra et al. evaluated the ability of the INVOS-3100 cerebral oximeter to detect cerebral ischemia induced by carotid cross-clamping in 99 patients undergoing carotid endarterectomy (CEA) during cervical plexus block. All patients had high-grade carotid artery stenoses (>70%) and were scheduled to undergo CEA during regional anesthesia. In addition to continuous monitoring of blood pressure, hemoglobin saturation, and regional cerebrovascular saturation (rSO2), bilateral rSO2was monitored simultaneously using two cerebral oximeters, with sensors were applied to both sides of patients’ foreheads. All rSO2readings were stored on computer for later off-line analysis. Minimal sedation with midazolam was administered before the cervical plexus block; additional 25–50 mg fentanyl was administered intravenously if patients were apprehensive. Neurologic function was assessed at 5-min intervals during occlusion by eliciting patient responses to verbal commands. Duration of carotid cross-clamp, development of any changes in neurologic function, and need for and time of insertion of shunt were recorded. Surgeons were not aware of the rSO2values during the operation and did not base their clinical management on the readings.
For analysis purposes, the rSO2data were divided into preclamp, cross-clamp, and postclamp phases, and mean values were calculated for each. At the end of the study, patients were assigned to one of two groups: those who did not show a change in neurologic function and those who did. Data from 94 operations were adequate for group comparisons. The mean decrease in rSO2after carotid occlusion was significantly greater in the group of patients who had neurologic symptoms (n = 10) than in the group with no symptoms. Researchers also analyzed whether a change in rSO2could be used to predict change in neurologic function. They found that a 20% decrease in rSO2reading from the preclamp baseline resulted in a sensitivity of 80% and a specificity of 82.2% as a predictor of neurologic compromise. However, the false–positive rate using this cut-off point was 66.7%. The positive predictive value was 33.3%, and the negative predictive value was 97.4%, which suggests that monitoring rSO2with a cerebral oximeter does not effectively predict the impending development of cerebral ischemia.