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

Abstract

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.

Acid‐base alterations in ESRD and effects of hemodialysis

“…Large interdialytic weight gain has been associated with mortality . Dilutional decline of serum HCO 3 − also contributes to the severity of predialysis acidosis . Thus, optimizing volume status and avoiding large interdialytic weight gain would likely mitigate pre‐HD acidosis, improve tissue oxygenation.…”

“…59 Dilutional decline of serum HCO 3 À also contributes to the severity of predialysis acidosis. 118 Thus, optimizing volume status and avoiding large interdialytic weight gain would likely mitigate pre-HD acidosis, improve tissue oxygenation. It should be a part of the basis for our current emphasis on reducing interdialytic weight gain -including patient education.…”

Bicarbonate Therapy in End‐Stage Renal Disease: Current Practice Trends and Implications

“…But since the intracellular bicarbonate concentration can be vastly different , the ABS becomes a very dynamic and rapidly changing entity. The ABS is highly variable, and it is influenced by the blood pH and by interdialytic weight gain (IDWG), which will ultimately affect the dialysate bicarbonate concentration that is needed to correct acidaemia .…”

Dialysate bicarbonate concentration: Too much of a good thing?

“… Acid generation rate : differences in endogenous acid production, largely determined by dietary protein intake, account for some of the interindividual variability in serum BIC; Inter‐dialysis weight gain : it lowers serum BIC by expanding the bicarbonate space; Time since last dialysis (ie, long vs short interval): serum BIC is approximately 1 mEq/L lower after the long interval than after the short interval; Phosphorus binder use : sevelamer hydrochloride reduces serum BIC, whereas phosphate binders containing alkali precursors do the opposite; Postdialysis serum BIC : the factors that determine the magnitude of the intra‐dialytic increase in serum BIC are also determinants of the predialysis serum BIC, as they determine the starting point for the progressive decline in serum BIC that typically occurs between HD treatments. …”