Contrasting Alterations in Pulmonary Gas Exchange during Acetate and Bicarbonate Hemodialysis

Abstract

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 VCO₂decreased 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.

Hemodialysis-AssociatedHypoxemia

“…Raja et al [ 12] observed a greater degree of hypoxemia when the concentration of acetate in the dialysate was 45 mM than when it was the usual value of 37 mM, suggesting that higher infusion rates of acetate -and, presumably, higher metabolic utilization of acetate -have a greater effect on reducing the respiratory quotient and increasing hypox emia. Eiser et al [20] similarly demonstrated a decreased respiratory quotient accompanied by hypoxemia and de creased minute ventilation during acetate dialysis; these authors also found, as had already been noted by Sher lock et al [15], that acetate dialysis resulted in increased consumption of oxygen which would obviously tend to compound the effect of decreased minute ventilation and be an added causal factor for hypoxemia. Interestingly, dialysis performed with C 0 2 bubbling in bicarbonatecontaining dialysate [20] was also accompanied by a drop in P a02 by an average of 10.3 mm Hg.…”

“…Eiser et al [20] similarly demonstrated a decreased respiratory quotient accompanied by hypoxemia and de creased minute ventilation during acetate dialysis; these authors also found, as had already been noted by Sher lock et al [15], that acetate dialysis resulted in increased consumption of oxygen which would obviously tend to compound the effect of decreased minute ventilation and be an added causal factor for hypoxemia. Interestingly, dialysis performed with C 0 2 bubbling in bicarbonatecontaining dialysate [20] was also accompanied by a drop in P a02 by an average of 10.3 mm Hg. No change in respiratory quotient was noted with bicarbonate dialysis: both oxygen consumption and C 0 2 production decreased by about 10%.…”

“…However, in a study by Romaldini et al [19], hypoxemia did not develop in a group of patients dialyzed with an acetate-containing bath, when CO2 was bubbled through the dialysate to maintain the partial pressure of CO2 in the blood returning to the patient at values close to those of the blood entering the dialyzer. Furthermore, Eiser et al [20] have shown that the use of a bicarbonate-containing dialysate may also result in hypoxemia, if no CO2 is bubbled in the dialysate. Finally, patients dialyzed with sorbent regenerative sys tems, which result in the formation of CO2 in the dialysis bath and its transfer to the blood compartment, develop an actual net gain of CO2 during dialysis [21] which in most patients is disposed of by increased pulmonary excretion, but in patients whose ventilation is controlled mechanically may cause acute hypercapnia.…”

“…Wathen et al [23] confirmed this observation in anesthetized dogs. Eiser et al [20] showed that acetate dialysis results in increased oxygen consumption and decreased C 0 2 production: Oh et al [17] confirmed that the reduction of respiratory quotient during acetate dial ysis is due only in minimal part to C 0 2 losses in the dia lyzer and that the most important component is a change in endogenous C 0 2 production and oxygen consump tion.…”

“…The data, however, also indicate that this endogenous change in respiratory quotient may not fully explain the hypoxemia of acetate dialysis, as some hypoxemia is also seen in the course of bicarbonate dialysis, when C 0 2 is not bubbled in the dialysate [12,20]. It must be emphasized, however, that the observa tions of Romaldini et al [19], who saw no hypoxemia in the course of dialysis with an acetate-containing dialysate when C 0 2 was bubbled into the bath, are difficult to reconcile with the notion that acetate infusion by itself necessarily changes the respiratory quotient; these obser vations, if confirmed, would argue against this mecha nism of production of hypoxemia.…”