Dialysate bicarbonate concentration: Too much of a good thing?

Logistic regression analysis was applied to a sample of more than 12,000 hemodialysis patients to evaluate the association of various patient descriptors, treatment time (hours/treatment), and various laboratory tests with the probability of death. Advancing age, white race, and diabetes were all associated with a significantly increased risk of death. Short dialysis times were also associated with high death risk before adjustment for the value of laboratory tests. Of the laboratory variables, low serum albumin less than 40 g/L (less than 4.0 g/dL) was most highly associated with death probability. About two thirds of patients had low albumin. These findings suggest that inadequate nutrition may be an important contributing factor to the mortality suffered by hemodialysis patients. The relative risk profiles for other laboratory tests are presented. Among these, low serum creatinine, not high, was associated with high death risk. Both serum albumin concentration and creatinine were directly correlated with treatment time so that high values for both substances were associated with long treatment times. The data suggest that physicians may select patients with high creatinine for more intense dialysis exposure and patients with low creatinine for less intense treatment. In a separate analysis, observed death rates were compared with rates expected on the basis of case mix for these 237 facilities. The data suggest substantial volatility of observed/expected ratios when facility size is small. Nonetheless, a minority of facilities (less than or equal to 2%) may have higher rates than expected when compared with the pool of all patients in this sample. The effect of various laboratory variables on mortality is substantial, while relatively few facilities have observed death rates that exceed their expected values. Therefore, we suggest that strategies designed to improve the overall mortality statistic for dialysis patients in the United States would be better directed toward improving the quality of care for all patients, particularly high-risk patients, within their usual treatment settings rather than trying to identify facilities with high death rate for possible regulatory intervention.

Experimental and some clinical data suggest that metabolic acidosis contributes to poor nutritional status, a strong predictor for mortality in hemodialysis patients. However, recent cross-sectional studies indicate that severe predialysis metabolic acidosis is associated with a greater normalized protein catabolic rate (nPCR) and greater serum albumin levels. Given this controversy, we analyzed data from the Dialysis Outcomes and Practice Pattern Study (DOPPS) for associations between predialysis serum bicarbonate and albumin concentrations, nPCR, and patient risk for mortality and hospitalization. Data from more than 7,000 representative and randomly selected hemodialysis DOPPS patients from France, Germany, Italy, Japan, Spain, the United Kingdom, and the United States were analyzed. Serum bicarbonate (total CO2 ) levels predialysis were corrected to the midweek interdialytic interval. The midweek predialysis serum bicarbonate level averaged 21.9 mEq/L (mmol/L) and correlated inversely with nPCR, serum albumin, and serum phosphorus values. Before and after adjusting for 15 comorbidities, nutrition, and equilibrated Kt/V, a U-curve best represented the association between predialysis serum bicarbonate level and risk for mortality or hospitalization. Patients with midweek predialysis serum bicarbonate levels of 20.1 to 21.0 mEq/L (mmol/L) faced the lowest risk for mortality, whereas those with bicarbonate levels of 21.1 to 22.0 mEq/L faced the lowest risk for hospitalization. Both high (>27 mEq/L) and low (< or =17 mEq/L) serum bicarbonate levels were associated with increased risk for mortality and hospitalization. Moderate predialysis acidosis seems to be associated with better nutritional status and lower relative risk for mortality or hospitalization than is observed in patients with normal ranges of midweek predialysis serum bicarbonate concentration (approximately 24 mEq/L) or severe acidosis (<16 mEq/L).

Most hemodialysis patients worldwide are treated with bicarbonate dialysis using sodium bicarbonate as the base. Few studies have assessed outcomes of patients treated with different dialysate bicarbonate levels, and the optimal concentration remains uncertain.