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, PaCO 2 , and HCO 3 , Prehemodialysis values (mean ′ SD) were pH = 7.34 ′ 0.03, PaCO 2 = 36.43 ′ 1.4, and HCO 3 = 20.1 ′ 1.55. Posthemodialysis values were pH = 7.47 ′ 0.02, PaCO 2 = 38.72 ′ 2.0, and HCO 3 = 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 HCO 3 (r = -0.836, p <0.001) and posthemodialysis pH (r = -0.533, p <0.001), PaCO 2 (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.