The anion gap of patients receiving bicarbonate maintenance hemodialysis

To compare the effect of maintenance bicarbonate hemodialysis on the serum anion gap (AG) and the serum HCO3, the authors retrospectively evaluated the data of 28 patients using the first-of-the-month blood chemistries. Data were available for at least 9 of the previous 12 months in each case. For the entire group, the average AG was 15.8 +/- 0.1 mEq/L and the HCO3 21.7 +/- 0.2 mEq/L. Comparing these values with the data compiled recently by three different groups of investigators in undialyzed patients with severe chronic renal failure indicates that the AG of the dialyzed patients was similar to that of untreated patients, but the HCO3 levels of dialyzed patients averaged 2 to 3 mEq/L higher. Separate prospective evaluation of the acute effect of two consecutive bicarbonate dialyses in 31 patients revealed that the average acute (immediate postdialysis) decrease (from predialysis values) in AG was only about 40% of that of the increase in HCO3. The authors conclude that bicarbonate dialysis is more effective in improving serum HCO3 than AG.