Carbon dioxide elimination during total cardiopulmonary bypass in infants and children

The authors measured the rate of carbon dioxide elimination (V̇CO₂) in 25 pediatric patients (age 2 days to 9 yr) during total cardiopulmonary bypass at average venous blood temperatures ranging from 19.5 to 35.9°C. A multiplexed mass spectrometer was connected to the gas inlet and exhaust ports of the bubble oxygenator, and the gas-phase Fick principle was used to determine V̇CO₂. A curvilinear relationship was found between log V̇CO₂ and venous blood temperature, and a quadratic regression equation (r² = 0.74) was fit to the data. Q₁₀ (the ratio of V̇CO₂ before and after a 10°C temperature change) was estimated to be 2.7 or 3.0, depending on the analytic method used. Venous blood temperature as a predictor variable explained a greater proportion of the variability of log V̇CO₂ than did nasopharyngeal or rectal temperatures. Analysis of covariance revealed that total circulatory arrest during bypass (utilized in 10 patients for 34 ± 4 min, mean ± SEM) affected the relationship of venous blood temperature with log V̇CO₂, by increasing the y-intercept (P = .008) but not the slope. These data, with associated 95% prediction intervals, define the expected CO₂ elimination rates at various temperatures during standard bypass conditions in our patients. Real-time measurement of V̇CO₂ using mass spectrometry can be a useful routine monitor during CPB that may help to assess patient metabolic function, adequacy of perfusion, and oxygenator performance.