In Vivo Demonstration of the Haldane Effect during Extracorporeal Gas Exchange

Abstract

During the extracorporeal support (LFPPV-ECCO₂R) of 11 patients suffering from severe lung failure (ARDS), we consistently noticed a higher arterial than mixed-venous PCO₂ in blood samples drawn at the same time. Two explanations are possible: a) the Haldane effect (HE), b) CO₂ from lung tissue metabolism. In order to distinguish changes in PCO₂ due to the HE from those due to tissue CO₂ production, CO₂ content (C_CO2) was calculated. The results were compared to animal experiments with hyperoxic apnea, after which arterial and mixed-venous samples were drawn simultaneously. All blood gas samples were analyzed for pH, PCO₂, PO₂, and 0₂-saturation, from which C_CO2 was calculated. In both groups, P_aCO₂ was 2.15 mmHg (2.7 mmHg respectively) higher at a lower C_aCO₂ (-2.87 ml/l, -14.9 ml/l). Oxygen saturation increased by 8.1% in the human group and 17.8% in the animal group. A significant relationship was found between changes in PCO₂ and changes in 0₂-saturation. This is a demonstration of the Haldane effect.