Objective: Cardiac surgery with cardiopulmonary bypass for correction of congenital heart disease in neonates and small infants is associated with considerable neurologic sequelae. We assessed the extent to which mixed venous oxygen saturation as a measure for adequacy of perfusion, reflects the oxygenation status of upper and lower body compartments. Moreover, we evaluated potential benefits of near-infrared spectroscopic monitoring of regional tissue oxygenation.
Methods: Twenty patients (body weight < 10 kg) undergoing open cardiac procedures with cardiopulmonary bypass were enrolled. Blood samples were obtained in parallel from inferior and superior caval vein cannulas and mixed venous line and assessed for venous oxygen saturation and lactate levels. Data were compared to simultaneously measured tissue oxygenation indices obtained by near-infrared spectroscopy from brain and lower limb.
Results: Venous oxygen saturation was lower and lactate concentration higher in blood from superior relative to inferior venous line. Mixed venous oxygen saturation correlated with venous oxygen saturation from inferior venous line and tissue oxygenation index of lower limb. No correlation was found between mixed venous oxygen saturation and venous oxygen saturation from superior venous line or cerebral tissue oxygenation index.
Conclusion: In neonates and small infants undergoing cardiac surgery with cardiopulmonary bypass, considerable regional differences exist in venous oxygen saturation. Mixed venous oxygen saturation primarily represents lower-torso oxygen status but poorly reflects and systematically overestimates upper-body oxygenation. Near-infrared spectroscopy yields additional information on regional oxygenation and may be valuable in early and sensitive detection of regional malperfusion in critical organs such as the brain.