AN OBSERVATIONAL STUDY OF NEAR-INFRARED SPECTROSCOPY DURING CAROTID ENDARTERECTOMY

Near-infrared spectroscopy was used to monitor changes in the cerebral oxygenation state in 13 patients during carotid endarterectomy. Varia tions in the levels of the chromophores (oxygenated hemoglobin (HbO(2) ), deoxygenated hemoglobin (Hb), and oxidized cytochrome (CytO(2))), a nd the total hemoglobin content (tHb) were compared with changes in mi ddle cerebral artery flow velocity measured using transcranial Doppler ultrasonography. Of eight patients who showed a fall in flow velocity on application of the internal carotid artery cross-clamp, seven demo nstrated a rapid and closely correlated fall in HbO(2) signal, and an increase in Hb. Levels of CytO(2) and tHb remained unchanged. During e ndarterectomy, recovery of the HbO(2) and Hb levels toward preclamp ba seline values occurred in three of these patients. Intraoperative shun ts accelerated recovery of HbO(2) and Hb signals in two of three indiv iduals. Release of the internal carotid cross-clamp resulted in a rapi d increase in HbO(2) and decrease in Hb signal in those patients in wh om spontaneous recovery had not occurred; in five instances, a hyperem ia evolved with raised now velocity and HbO(2) to above baseline value s. Cross-clamping and subsequent reperfusion of the external carotid a rtery had no effect on any parameter measured. The authors conclude th at near-infrared spectroscopy can register changes in cerebral oxygena tion during carotid endarterectomy without significant contamination f rom extracranial tissues.