Near-infrared monitoring of cerebral oxygenation state during carotid endarterectomy

Abstract

Recent studies have indicated that near-infrared spectroscopy (NIRS) could continuously and noninvasively observe the changes in cerebral oxygenation state during hypoxia and ischemia, using their optical properties. Its validity and usefulness during cerebrovascular surgery, however, still remain to be clarified. Using NIRS, we continuously monitored the changes in the concentration of oxyhemoglobin, deoxyhemoglobin, and total hemoglobin ([oxy-HB], [deoxy-Hb], and [total Hb], respectively) and redox state of cytochrome oxidase (cyt ox) during carotid endarterectomy for 22 patients, and we compared the NIRS responses with those of intraoperative somatosensory evoked potentials (SEP) and regional cerebral blood flow (rCBF). In 9 of 22 patients, cross-clamping of the carotid artery caused a continuous decrease [oxy-Hb] and [total Hb], and an increase in [deoxy-Hb]. Cyt ox was partially reduced during the clamping. These NIRS responses demonstrated the occurrence of severe hypoxia in the ipsilateral cerebral tissue. These patients showed a marked decrease in the N20 amplitude of SEP and rCBF. In contrast, the other 13 patients did not show a significant decrease in the cerebral oxygenation state, which showed no remarkable changes in either SEP or in rCBF. NIRS could successfully jude the cerebral oxygenation state noninvasively during carotid surgery and was more sensitive to ischemic crisis than other indirect methods.