Cerebral oxygenation during cardiopulmonary bypass measured by near-infrared spectroscopy: Effects of hemodilution, temperature, and flow

Objective:To determine the effects of hemodilution, PaCO2, PaO2, arterial p ressure, and temperature on cerebral oxygenation during mild hypothermic ca rdiopulmonary bypass (CPB). Participants: Fourteen patients electively scheduled for cardiac surgery. Interventions: Oxyhemoglobin (HbO(2)), deoxyhemoglobin (Hb), hemoglobin dif ferential (Hb-diff = HbO(2)-Hb), and oxidized cytochrome aa(3) (CtO(2)) wer e measured with near-infrared spectroscopy (NIRS) during CPB. Results: With onset of CPB, a significant decrease in HbO(2) (median, -4.55 mu mol/L; 25th to 75th percentile, -5.5 to -3.1; p <0.05), Hb-diff (median , -3.88 mu mol/L; 25th to 75th percentile, -4.7 to -1.9; p < 0.05), and CtO (2) (median, -0.05 mu mol/L; 25th to 75th percentile, -0.15 to 0; p < 0.001 ) occurred. The simultaneous decrease in arterial hemoglobin concentration (from 11.7 to 8.5 g/100 mL, p < 0.005) correlated significantly with change s in HbO(2) (r(2) = 0.71; p < 0.001), Hb-diff (r(2) = 0.59; p < 0.005), and CtO(2) (r(2) = 0.57; p < 0.005). After 24 minutes of CPB, the largest decl ine in HbO(2) (-5.03 mu mol/L) and Hb-diff (-5.68 mu mol/L) was recorded, w hereas CtO(2) showed no changes during cooling. During CPB, Hb and Hb-diff significantly correlated with the duration of CPB, PaO2 and PaCO2. Conclusions: In early stages of CPB, a diminished cerebral oxygen supply wa s found, which may be caused by acute hemodilution. Despite an increased ex traction of oxygen as demonstrated by the decrease in Hb-diff, cerebral ene rgy balance reflected by CtO(2) was maintained within a safe range during c ooling. Because NIRS measures regional cerebral oxygenation, it is useful a s an adjunct to global measures in the early noninvasive detection of cereb ral hypoxia. Copyright a 1999 by W.B. Saunders Company.