Mixed Venous-Arterial CO 2 Tension Gradient after Cardiopulmonary Bypass

Significant venous hypercarbia has been reported in septic shock and circulatory failure. Cardiopulmonary bypass also impairs systemic and pulmonary blood perfusion. The objective of this study was to determine the clinical significance of the increased venous-arterial CO₂ tension gradient resulting from venous hypercarbia after cardiopulmonary bypass. On arrival in the intensive care unit, venous and arterial CO₂ tensions were measured in the radial and pulmonary arteries in 140 consecutive patients who had undergone coronary (n = 79), valve (n = 34), aortic (n = 20), and other (n = 7) surgery under cardiopulmonary bypass. The mean venous-arterial CO₂ tension gradient was 5.0 ± 3.3 mm Hg (range, 7.7 to 15.7 mm Hg). By linear regression analysis, the factors that significantly correlated with venous-arterial CO₂ tension gradient were bypass duration, aortic crossclamp time, initial arterial lactate level, transpulmonary arteriovenous lactate difference, arterial bicarbonate level, base excess, cardiac index, mixed venous O₂ saturation, O₂ delivery, O₂ consumption, and the peak value of creatine kinase. The venous-arterial CO₂ tension gradient may reflect impaired perfusion and anaerobic metabolism induced by cardiopulmonary bypass and could be a simple and useful indicator for patient management after surgery under cardiopulmonary bypass.