Relationship Between Interdialytic Weight Gain and Acid-Base Status in Hemodialysis by Bicarbonate

: The aim of this study was to determine the relationship between interdialytic weight gain and acid‐base balance pre‐ and posthemodialysis in uremic patients undergoing hemodialysis with a high bicarbonate dialysate (39 mmol/L). To this end we studied 8 stable uremic patients on regular hemodialysis thrice weekly who had stable hematocrit values for at least 3 months, similar clinical characteristics including dry weight but widely varying interdialytic weight gain. Arterial line blood samples were collected anaerobically in heparinized syringes pre‐ and posthemodialysis in 4 consecutive hemodialysis sessions for the determination of pH, Paco2, and HCO3. Prehemodialysis values (mean ± SD) were pH = 7.34 ± 0.03, Paco2 = 36.43 ± 1.4, and Hco3 = 20.1 ± 1.55. Posthemodialysis values were pH= 7.47 ± 0.02, Paco2 = 38.72 ± 2.0, and HCO3 = 27.73 ± 1.72. In other words, patients were moderately acidemic prior to and moderately alkalemic after the hemodialysis session. Of note, a significant negative correlation was revealed between the interdialytic weight gain and the values of prehemodialysis blood pH (r = −0.721, p < 0.001) and HCO3 (r = −0.836, p < 0.001) and posthemodialysis pH (r = −0.533, p < 0.001), Paco2 (r = −0.623, p < 0.001) and HCO3 (r = −0.815, p < 0.001), suggesting an important role of the interdialytic weight gain on acid‐base equilibrium of uremic patients undergoing hemodialysis. Thus, patients with high interdialytic weight gains may require higher bicarbonate concentrations to achieve normal acid‐base status whereas patients with low interdialyic weight gains may require lower bicarbonate concentrations to prevent alkalemia at the end of dialysis.