Pulmonary Gas Exchange during Metabolic Acidosis. II. Experimental Studies about Causes of Paradoxical Increase of PaO2

In order to make clear the causes of paradoxical increase of Pa O2 during severe metabolic acidosis, three experiments were performed. A: In vitro study. Hydrochloride of 0.1 N, 0.1 ml was added anerobically to each 0.9 ml of saline, arterial blood, red cell suspension and diluted serum. Red cell suspension and diluted serum were produced by diluting procedures with bicarbonate buffer and equilibrating with air and carbon dioxide. The pH value, P O2, and P CO2 of these fluids were measured prior to and after the addition of HCl. B: In vivo study. Rabbits and dogs were loaded with 0.15?0.5 N HCl infusion at a speed of 0.4?1.0 ml/kg/min. The pH value, Pa O2, PV O2, FE O2 and FE CO2 were measured prior to and after the load. A-a D O2 and RQ were calculated from these data. C: Computer Simulation. The effect of PV O2 on Pa O2 was simulated while PA O2 and pulmonary shunt rate were unchanged. The following results were obtained. A: The pH values of all liquids decreased significantly after the addition of HCl. P CO2 increased significantly after the addition of HCl, except for saline. P CO2 of saline did not change. P O2 of arterial blood and red cell suspension increased significantly after the addition of HCl but the P O2 of the others did not change. B: Pa O2, PV O2 and RQ increased significantly after the HCl load. The pH value and A-a D O2 decreased significantly after the HCl load. C: The increase of Pv O2 made Pa O2 higher. The higher the pulmonary shunt rate became, the more the Pa O2 increased while the elevation of Pv O2 was constant. In conclusion, the causes of the paradoxical increase of Pa 02 during severe metabolic acidosis were not the abnormal reactions of the electrode, but rather the increases of RQ and PV O2 without pulmonary function improvement