Re-evaluation of the reliability of cytochrome oxidase--signal study of cardiopulmonary bypass.

Abstract

The monitoring of brain oxygen status using near-infrared spectroscopy (NIRS) has recently been applied to clinical practice in the field of cardiovascular surgery. Published studies have indicated that NIRS could be used as a continuous and noninvasive way of observing changes in the cerebral oxygenation state during hypoxia and ischemia, since changes occur in optical properties under these conditions. However, the interpretation of NIRS data, especially the cytochrome oxidase (cyt. ox.) signal, remains controversial. A possible source of error that might interfere with the accurate measurement of the redox state of cyt. ox. derives from an overlapping of the absorption spectra for hemoglobin and cyt. ox. in the near-infrared region, with the absorption coefficient for hemoglobin being an order of magnitude greater than that for cyt. ox.. Recently, it was reported that the cyt. ox. signal measured by near-infrared spectroscopy (NIRS) is highly contaminated with the hemoglobin signal [1]. However, the cyt. ox. signal measured by NIRS would be expected to be strongly dependent on the algorithm employed. We have developed a new approach to the measurement of the redox state of cyt. ox. in the brain involving the use of a new algorithm [2], which has already been employed in clinical medicine [3, 4]. Therefore, in this paper we looked for evidence of cross-talk between the cytochrome and hemoglobin (Hb) signals when our new algorithm was used under cardiopulmonary bypass (CPB) in a dog model. Furthermore, we retrospectively studied the relationship between data obtained concerning the redox behavior of cyt. ox. during surgery (again using our new algorithm) and neurological prognosis in 105 patients.