Dialysate sodium and interdialytic weight gain

Hemodialysismedium

A 50-year-old man with ESKD undergoing HD thrice weekly for the past 4 years presents to the outpatient dialysis unit with persistent large interdialytic weight gain (IDWG). He has received counseling on dietary fluid restriction, and his dialysis treatment time was increased 2 months ago. IDWG is typically 3–4 kg during the mid-week intervals and 6–8 kg over the long interdialytic interval. He estimates his urine output to be 100 mL/d. Current HD prescription includes 4-hour treatment, blood flow rate (BFR) of 450 mL/min, dialysate flow rate of 700 mL/min, and a dialysate composition that includes sodium concentration of 140 mEq/L, bicarbonate concentration of 35 mEq/L, and potassium concentration of 2 mEq/L. He dialyzes via an arteriovenous fistula (AVF) and most recent Kt/V is 1.82 (reference range, >1.2). Current medications include torsemide, lisinopril, calcium acetate, and calcitriol. On examination prior to HD, BP is 158/86 mm Hg and heart rate is 86/min. His lungs are clear, a right forearm AVF has a strong thrill, and trace bilateral lower extremity edema is present. What is the MOST appropriate next best step in the management of this patient’s large IDWG?

  1. A.Change torsemide to bumetanide
  2. B.Increase the patient's target weight
  3. C.Decrease dialysate sodium concentrationCorrect
  4. D.Add a weekly sequential ultrafiltration session

Explanation

The most appropriate next step for this patient with large IDWG is to decrease the dialysate sodium concentration. Patients with ESKD and increased IDWG are at higher risk for cardiovascular complications. Many patients receiving HD have serum sodium concentrations that are lower than that of the dialysate. This gradient drives the diffusion of sodium from dialysate to plasma (”sodium loading”), which increases thirst and subsequent fluid intake. Increases in serum sodium by using a higher dialysate sodium bath may trigger a relative free-water deficit leading to fluid ingestion during the interdialytic period. For patients with large IDWG, a multidisciplinary approach is often used that includes education about fluid and dietary sodium restriction, optimization of diuretics in patients with residual renal function, optimizing the dialysis time, and lowering the dialysate sodium concentration closer to the patient’s underlying serum sodium level. Several small studies have shown improvements in IDWG after lowering dialysate sodium concentration, although the specific sodium gradient reduction to achieve this benefit is not well defined. This patient has minimal urine output, and changing from torsemide to bumetanide is unlikely to have a meaningful impact of increasing urine output or IDWG. Some patients require HD more than 3 times a week or ultrafiltration to maintain their target weights. However, given the lifestyle burdens this will impose on the patient, lowering the dialysate sodium concentration is a better option. Should a reduction in dialysate sodium concentration not be sufficient, the patient may benefit from additional scheduled treatments. Increasing the target weight would not be appropriate, because this patient has signs of volume overload, which would likely worsen at a higher target weight.

Why each option

A.
With urine output of only 100 mL/day, switching one loop diuretic for another will not meaningfully increase urine volume or reduce interdialytic weight gain.
B.
Raising target weight is inappropriate in a hypertensive patient with edema, because it accepts and worsens existing extracellular volume overload.
C.
Correct. A 140 mEq/L dialysate above serum sodium loads sodium during dialysis, driving thirst; lowering it toward serum sodium reduces interdialytic weight gain.
D.
Extra ultrafiltration sessions add treatment burden and should follow, not precede, removing the diffusive sodium load that drives thirst between sessions.

Reference: KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 Update (Am J Kidney Dis 2015); Dunlop JL, Cochrane Database Syst Rev 2019 (low dialysate sodium in maintenance hemodialysis)

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