Relation of Interdialytic Water Retention with Apparent Bicarbonate Space, HCO3−, and pH in Hemodialyzed Uremic Patients

This study determines the relationship between interdialytic water retention (IWR) and acid-base homeostasis in uremic patients under regular hemodialysis (HD). To this aim, in 33 regular bicarbonate HD sessions of 11 uremic patients (three HD sessions of 1 week for each patient), blood samples were received from arterial line immediately pre- and post-HD anaerobically in heparinized syringes and the HCO3−, pH, and pco2 were determined. Also in the studied HD sessions, the IWR was estimated and the apparent bicarbonate space percentage (ABS%) pre- and post-HD was calculated by Fernandez et al. (Eq. 1). The mean ± SD values pre-HD (ABS%=54.15 ± 1.49, HCO3−=18.54 ± 2.0 mmol/L, pH=7.32 ± 0.02, pco2=35.44 ± 3.10 mmHg) and post-HD (ABS%=49.88 ± 0.6, HCO3−=26.33 ± 1.6 mmol/L, pH=7.44 ± 0.02, pco2=37.69 ± 3.00 mmHg) show metabolic acidosis pre-HD and slight alkalosis post-HD. There was a significant positive correlation between IWR and ABS% pre-HD (r = 0.650, p < .0001) and post-HD (r = 0.655, p < .0001), but a significant negative correlation between IWR and HCO3− pre-HD (r = − 0.502, p < .003) and post-HD (r = − 0.700, p < .001), as well as between IWR and pH pre-HD (r = − 0.516, p < .002) and post-HD (r = − 0.377, p < .03). In addition, there was a significantly negative correlation between IWR and pco2 post-HD (r = − 0.656, p < .001), but not pre-HD (r = 0.0136, PNS). The significantly positive relationship between IWR and ABS% pre- and post-HD, in combination with the significantly negative correlation between HCO3− and pH pre- and post-HD, indicates that the IWR negatively influences the acid-base homeostasis in hemodialysis patients without residual renal function, and may worsen the cardiovascular physiology and tissue oxygenation of these patients.