Hemodynamic evaluation by using near infrared spectroscopy during carotid endarterectomy

To evaluate the hemodynamic changes during carotid endarterectomy, we compared changes in oxyhemoglobin levels with changes in the internal carotid artery flow and the somatosensory evoked potential (SEP). In 40 of 42 patients, the oxyhemoglobin level, measured in the frontal area on the operated side using near infrared spectroscopy (NIRS), decreased immediately after cross-clamping the internal carotid artery and returned to the preclamping level after the clamp was removed. There was no linear relationship between the internal carotid flow and the decrement in the oxyhemoglobin level after carotid clamping. Nineteen patients (45%) had a large internal carotid flow (> or =90 mL/min), but a small decrease in the oxyhemoglobin level (<0.04 in index); presumably these patients had adequate collateral circulation. Eight patients (19%) had a large internal carotid flow and a marked decrease in the oxyhemoglobin level (> or =0.04); presumably these patients had insufficient collateral circulation. The changes in oxyhemoglobin and SEP after carotid clamping agreed in 77.5% of the patients; however, in the other 22.5%, the disparity between the two factors indicated different causes of cerebral ischemia following carotid clamping. A marked decrease in oxyhemoglobin without a significant change in SEP suggests ischemia predominantly in the frontal area, whereas a small decrease in oxyhemoglobin and a significant change in SEP suggest ischemia predominantly in the somatosensory pathway or cortex. In conclusion, the relationship between the internal carotid flow and the change in HbO(2) provides information about the collateral circulation. Simultaneous monitoring of NIRS and SEP is useful for assessing of the pattern of cerebral ischemia during carotid clamping.