Monitoring of brain oxygen status using near-infrared spectroscopy

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Although the signal obtained for cytochrome oxydase (cyt. ox.) by near-infrared spectroscopy (NIRS) should be a useful indicator of intracellular hypoxia, the cyt. ox. signal represents a small component of the total change, and is therefore vulnerable to artifact. Recently it has been reported that cyt. ox. signal measured by NIRS is highly dependent on hematocrit. We have developed a new approach to the measurement of cyt. ox. in the brain involving the use of our new algorithm. In this study, we used NIRS device with our algorithm to examine possible cross-talk between the cytochrome and Hb signals while a change was occurring in the hemodilution. In another experiments, deep hypothermic circulatory arrest (DHCA) was induced for 60 min under 25℃ or 15℃ and evaluated the relationship between the redox behavior of cyt. ox. during DHCA and postoperative neurological prognosis. After institution of cardiopulmonary bypass (CPB), dogs received sodium cyanide to uncouple cytochrome from Hb. The hematocrit was then decreased from 35 to 5% by hemodilution. In this study, the Hb concentration calculated by NIRS device showed a strong positive correlation with hematocrit values in the blood during hemodilution. However, there was no correlation between the hematocrit and the cyt. ox. signal, which indicate that the cyt. ox. signal calculated using our recently developed algorithm was not much influenced by hematocrit. Furthermore, there was a good correlation between the redox behavior of cyt. ox. in the brain during DHCA and postoperative brain injury. In conclusion, the cyt. ox. signal measured by NIRS is dependent on the algorithm employed. Therefore, provided an accurate algorithm is employed the cyt. ox. signal measured by NIRS should provide us with important information even under various changes in hematocrit and/or hypothermia.