Bicarbonate Balance and Prescription in ESRD

Abstract

The optimal approach to managing acid-base balance is less well defined for patients receiving hemodialysis than for those receiving peritoneal dialysis. Interventional studies in hemodialysis have been limited and inconsistent in their findings, whereas more compelling data are available from interventional studies in peritoneal dialysis. Both high and low serum bicarbonate levels associate with an increased risk of mortality in patients receiving hemodialysis, but high values are a marker for poor nutrition and comorbidity and are often highly variable from month to month. Measurement of pH would likely provide useful additional data. Concern has arisen regarding high-bicarbonate dialysate and dialysis-induced alkalemia, but whether these truly cause harm remains to be determined. The available evidence is insufficient for determining the optimal target for therapy at this time.

Keywords: acidosis; dialysis; electrolytes.

Figure 1.

Change in serum bicarbonate during hemodialysis correlates directly with dialysate-serum gradient and inversely with predialysis concentration. Intradialytic change in serum bicarbonate versus (A) dialysate–serum bicarbonate gradient and (B) predialysis serum bicarbonate level among chronic hemodialysis patients dialyzed against 35 mEq/L (15 patients, Uribarri et al.); 36 mEq/L (70 patients, Sepandj et al.); and 25, 30, or 35 mEq/L (53 patients, Noh et al.) bicarbonate dialysate. Data from Uribarri et al., Sepandj et al., and Noh et al. Intradialytic increase in serum bicarbonate per 1 mEq/L higher predialysis serum bicarbonate = −0.55 mEq/L (95% confidence interval [95% CI], −0.68 to −0.43); for individual studies, the slope was −0.54 mEq/L (95% CI, −0.81 to −0.28) for Uribarri et al., −0.55 mEq/L (95% CI, −0.69 to −0.41) for Sepandj et al., and −0.43 mEq/L (95% CI, −0.66 to −0.20) for Noh et al. P for interaction by study = 0.63.

Figure 2.

Theoretical bicarbonate profiles in hemodialysis. Profiles of serum bicarbonate changes for patients receiving hemodialysis with midweek predialysis serum bicarbonate of 20 and 28 mEq/L, respectively. Profiles assume dialysate bicarbonate of 35 mEq/L and intradialytic increases on the basis of point estimates derived from linear regression of data from Uribarri et al. and Sepandj et al. (predicted intradialytic increase 7.7 mEq/L [95% confidence interval, 7.2 to 8.3] and 2.8 mEq/L [95% confidence interval, 2.1 to 3.5] for predialysis serum bicarbonate of 20 and 28 mEq/L, respectively).

Figure 3.

Daily acid-generation rate correlates inversely with predialysis serum bicarbonate level in patients receiving hemodialysis. All patients with daily acid-generation rates above the mean (28 mEq/L) had predialysis serum bicarbonate <24 mEq/L. Data from Uribarri et al. (n=15).