Near infrared spectroscopy (NIRS) is a noninvasive and real-time method for monitoring oxy-[HbO2] and deoxyhemoglobin [Hb] in tissue, and is suitable for intraoperative monitoring. In this study, NIRS monitoring was performed on 10 patients during carotid cross-clamping. The data were analyzed with a theoretical cerebral hemoglobin model developed to identify an ischemic pattern using NIRS parameters. Temporal profiles of changes in [HbO2] and [Hb] were divided into three phases: initial (immediately after clamping), second (during clamping), and last phase (immediately after clamp release). In the initial phase, [HbO2] decreased and [Hb] increased in all the cases. In the second phase, recovery patterns of [HbO2] were classified into three groups: complete (3 patients), incomplete (3 patients), and no recovery (2 patients). In the last phase, the [HbO2] increased and [Hb] decreased. Relative changes in [HbO2] and [Hb] measured by NIRS were correlated with changes in blood flow of the internal carotid artery (ICA)measured by a magnetic flowmeter and stump pressure of the internal carotid arteries. The degree of [HbO2] decrease in the initial phase was significantly correlated with ICA blood flow before clamping (r=0.90, p<0.05). Three of the 4 patients with ICA stump pressure over 50 mmHg showed a complete recovery pattern in the second phase,
while all 4 patients with ICA stump pressure under 50 mmHg showed an incomplete recovery or no recovery pattern with NIRS. These results suggest that NIRS is useful in evaluating changes in cerebral blood flow and the extent of hemodynamic reserve during carotid cross-clamping.