Utility of near-infrared spectroscopic measurements during deep hypothermic circulatory arrest

Background. Near-infrared spectroscopy (NIRS) is used to monitor cerebral o xygenation during cardiac surgery. However, interpretation of the signals i s controversial. The aim of the study was to determine which NIRS variable best correlated with brain damage as assessed by animal behavior and neuroh istologic score and to compare the accuracy of NIRS and magnetic resonance spectroscopy (MRS) in predicting brain injury. Methods. Forty 5-week-old piglets underwent 60 minutes of deep hypothermic circulatory arrest (DHCA) at 15 degrees C. Changes in brain adenosine triph osphate (ATP), phosphocreatine (PCr), and intracellular pH (pHi) were deter mined by MRS and correlated to changes in oxygenated hemoglobin (HbO(2)), d eoxygenated hemoglobin (Hb), and oxidized cytochrome a,a(3) (CytOx) NIRS si gnals. Brains were fixed on day 4 and examined using a neurohistologic scor e. Results. Reductions in CytOx and HbO(2) values were correlated closely with decreases in ATP, PCr, and pHi. The changes in CytOx: and PCr showed the s trongest correlation (r = 0.623). Maximal CytOx reduction during DHCA of mo re than -25 mu M * differential pathlength factor (DPP) predicted brain dam age with a sensitivity of 100% and a specificity of 75%. The histologic sco re was also correlated with a decrease in ATP (r = -0.52 for CytOx; r = -0. 32 for ATP); HbO(2) PCr, and pHi showed no correlations. Conclusions. Reduction in CytOx correlates with decreased brain energy stat e and predicts histologic brain injury after DHCA with a high sensitivity. These data suggest that the level of CytOx could be a very important predic tor of brain damage during DHCA. (C) 2000 by The Society of Thoracic Surgeo ns.