Background and PurposeNear-infrared spectroscopy is a technique that can potentially monitor changes in cerebral oxygenation. There are at present limited clinical data regarding the value of this technology in relating neurological outcome to cerebrovascular hemoglobin oxygen saturation (Sco2). This investigation reports changes in Sco2due to carotid cross-clamping during carotid endarterectomy in awake patients.MethodsSco2was monitored in 38 adult patients undergoing 41 carotid endarterectomies under regional anesthesia. Ipsilateral and contralateral hemispheres were monitored simultaneously during 36 operations, with ipsilateral monitoring alone in the remaining 5 operations.ResultsNo significant difference was detected between ipsilateral and contralateral Sco2during preclamp or postclamp periods. Carotid cross-clamping caused a statistically significant (P < .01) decrease in the ipsilateral Sco2, which decreased from 71.8 +/- 6.91% to 65.8 +/- 8.2%, while the contralateral Sco2remained stable at 70.5 +/- 7.5% and 70.3 +/- 7.9%. The change in ipsilateral Sco2ranged from positive 2.6% to negative 28.6% of the preclamp value. The difference between ipsilateral and contralateral Sco2during cross-clamping was statistically significant (P < .001). The duration of cross-clamping was 39 +/- 11 minutes (range, 18 to 89 minutes). The decrease in ipsilateral Sco2was highly variable from patient to patient and did not correlate with the duration of cross-clamping.ConclusionsThese results suggest that carotid artery occlusion causes a statistically significant but variable decrease in Sco2in the majority of patients. Data in this investigation provide a range of Sco2values that was not associated with a clinically detectable neurological dysfunction.(Stroke. 1996;27:49-55.)