Redox behavior of cytochrome oxidase and neurological prognosis in 66 patients who underwent thoracic aortic surgery.

OBJECTIVE Using near-infrared spectroscopy (NIRS), we have developed a new approach to the measurement of the redox state of cytochrome oxidase (cyt. ox.) in the brain. Our previous animal study showed that oxygen-dependent redox changes in cyt. ox. occur only when oxygen delivery is badly impaired. Therefore, in this study, we retrospectively examined the relationship between the redox behavior of cyt. ox. (measured by NIRS) during an operation and the neurological outcome in patients. METHODS We studied 66 patients undergoing thoracic aortic surgery with cardiopulmonary bypass. Cerebral oxygenation was monitored by NIRS, and relative values for the concentrations of oxy-Hb, deoxy-Hb, and the redox state of cyt. ox. in the brain were calculated using our developed algorithm. RESULTS Retrospective assessment revealed three different types of cyt. ox. behavior: (1) no change (type-A) in 34 cases (51.5%), (2) a temporary reduction, with a subsequent return to the pre-surgery baseline level (type-B) in 29 cases (43.9%), or (3) a marked and prolonged reduction (type-C) in only three cases (4.5%). Nine of the 66 patients (13.6%; one type-A, five type-B, and all three type-C patients) showed evidence of postoperative brain injury (in the type-A patient, the injury proved to be localized and far from the monitoring site). The relationship between the occurrence of such an injury and the type of cyt. ox. behavior seen during the operation was highly significant (P<0.0001; chi-square test for independence). CONCLUSIONS Our data suggest that the redox behavior of cyt. ox. during an operation is a good (though not perfect) predictor of postoperative cerebral outcome, and that overall tissue oxygen sufficiency can be confirmed by near-infrared measurement of cyt. ox.