Abstract
Near-infrared spectroscopy (NIRS) is a non-invasive methodology that can monitor the change of cerebral oxygenation state continuously. In the present report, we describe our 9 years of experience using NIRS monitoring during carotid endarterectomy in 55 patients, during carotid balloon occlusion test in 16 and during vertebral artery transposition in 4. The results were compared with those of somatosensory evoked potential (SEP), transcranial Doppler sonography (TCD) and single photon emission computed tomography (SPECT). The pattern of NIRS change could be classified into 2 groups: Group 1 showing no change or transient decrease of total hemoglobin and hemoglobin oxygenation and Group 2 showing continuous decrease of these parameters. N20 amplitude significantly decreased during carotid artery occlusion in Group 2 patients, but did not show any change in Group 1 patients. The mean flow velocity ratio of the middle cerebral artery decreased to less than 38% of the control during carotid artery occlusion in Group 2 patients, but was kept more than 65% of the control in Group 1 patients. Regional cerebral blood flow in the ipsilateral frontal lobe reduced to less than 82% of the contralateral side in Group 2 patients, whereas it was more than 90% in Group 1 patients. Therefore, NIRS could accurately detect critical cerebral ischemia during carotid artery occlusion with good time resolution. In conclusion, NIRS is very useful to detect cerebral ischemia very quickly and accurately, but a combination of NIRS with other monitoring systems is preferable to enhance the value of NIRS and make up for its limitations. We discuss the usefulness and disadvantages of NIRS for intraoperative monitoring in neurosurgery.
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