Contrasting alterations in pulmonary gas exchange during acetate and bicarbonate hemodialysis

We studied 10 patients during acetate and 10 patients during bicarbonate hemodialysis to assess changes of minute ventilation; oxygen consumption (VO2); and carbon dioxide production (VCO2) as well as pO2, pCO2 and pH. We also measured the extent of pulmonic shunting by administering 100% O2. Our studies revealed that VO2 increased significantly during acetate dialysis, while it decreased slightly during bicarbonate dialysis. Since VCO2 decreased with both baths, the respiratory exchange ratio (R) decreased during acetate dialysis but did not change during bicarbonate dialysis. By the alveolar gas equation, these changes in R could account for a difference in alveolar pO2 and consequently arterial pO2. The fact that pO2 fell during bicarbonate dialysis may relate to decreased minute ventilation paralleling decreases in VCO2. The degree of intrapulmonic shunting was not altered during dialysis with either bath. We conclude that hypoxemia during dialysis relates to decreases in minute ventilation and that a greater decrease during acetate dialysis is a consequence of enhanced VO2 and its effect on R. Bicarbonate dialysis does not increase VO2.