How to Adjust the Sodium Concentration in Dialysate Individually and Practically?

Abstract

The optimal dialysate sodium concentration for chronic hemodialysis patients remains controversial. Conflicting data from small observational studies and large cohort study data have not convinced nephrologists to choose either a high or low sodium dialysate. Despite a lack of evidence, I would prescribe individualized dialysate sodium concentrations for patients with a risk of hypertension or volume overload, aligning the dialysate sodium concentration with patients’ predialysis serum sodium level. The concentration of dialysate sodium would usually be 0–2 mEq/L below the patient’s serum sodium concentration. I believe that this strategy would help improve hypertension, intradialytic weight gain, cardiac outcomes, and deliver precision medicine.

Specific Aim: “You are being put in charge as the Medical Director of a newly built dialysis clinic in your country. In consideration of available resources and reimbursement policies, how would you prescribe the dialysate sodium concentration for your patients? What would your approach be and why?”

I would advocate three steps in prescribing the dialysate sodium concentration for patients in my dialysis clinic.

First, choose a default dialysate sodium concentration of 138 mEq/L for all new patients.

Irrespective of the price of dialysate fluids with different sodium concentrations in United States, I would prescribe a default dialysate sodium concentration of 138 mEq/L for all new patients, because most patients’ serum sodium concentration is relatively constant [1,2], averaging around this number [3,4].

I would not align the dialysate sodium concentration with the patient’s serum sodium concentration, when just starting dialysis, given that the patient’s serum sodium concentration varies when measured at different volume states. The patients will be able to adjust their salt and fluid intake to reach their own natremic set point [4]. It is easier for the dialysis unit to routinely start a new patient, with a dialysate sodium concentration of 138 mEq/L.

Second, after three months, I would assess each patient. For high-risk patients, I would individualize the dialysate sodium concentration by aligning it with the patients’ predialysis serum sodium concentration.

Clinicians will assess each patient’s serum sodium concentration, blood pressure (BP) and volume status during the monthly unit rounds. With continuous education about a low sodium diet and fluid restriction, they will adjust the estimated dry weight (EDW) for each patient. Optimization of the dialysate sodium prescription has been shown to be an important step in achieving sodium balance, improving BP control in hypertensive hemodialysis patients [2], and improving inter-dialytic weight gain (IDWG) [5]. I would therefore utilize individualized dialysate sodium concentrations for specific patients who have issues with volume overload.

Three months after starting hemodialysis in our unit, I would review all the data related to each patient’s BP. For patients who have problems with BP, IDWG, or post-dialysis weight above dry weight, I would lower the dialysate sodium concentration to 0–2 mEq/L below the serum concentration, with a minimum dialysate sodium concentration of 135 mEq/L. Details are shown in the paper published in Hemodialysis International [6]. The rationale for this is to have a neutral sodium gradient during dialysis, which means no sodium diffusing through the dialysis membrane, to avoid extra sodium loading [7,8]. Setting the dialysate sodium concentration approximately 2 mEq/L below the serum sodium concentration is considered to be a neutral gradient.

Varying the dialysate sodium concentration gradient with the patient’s serum sodium concentration has different effects on BP and IDWG [5,9]. Therefore, individualized dialysate sodium concentrations are recommended [2,3,10].

Third, maintenance of the dialysate sodium concentration prescription.

Every three months, I would assess each patient’s volume status, BP, IDWG, post-dialysis weight versus EDW, and serum sodium concentration. For patients who have evidence of hypertension, high IDWG, or fail to reach EDW, I would further adjust the dialysate sodium concentration if needed, and address sodium and fluid restriction.

The DOPPS (the Dialysis Outcomes and Practice Patterns Study) data, showing that patients with lower serum sodium who are dialyzed with a higher sodium dialysate concentration have a lower mortality, are intriguing [11]. However, multiple studies suggest the hyponatremia itself is associated with increased risk of death [12,13,14]. I am more concerned that loading more sodium on patients during hemodialysis will worsen hyponatremia.

I would keep most patients on a lower dialysate sodium concentration once prescribed. I have not observed more intra-dialytic hypotension in our unit after lowering the dialysate sodium concentration. I do increase the dialysate sodium concentration up to 138 mEq/L if a patient becomes hypotensive, with no sign of volume overload, as some frail patients may benefit from a higher dialysate sodium concentration [11,15]. Most importantly, I would not prescribe a dialysate sodium concentration below 135 mEq/L [6].

Conclusions: With the above strategy, the dialysis unit would be able to focus on those patients with volume issues. A consensus on these procedures is needed among all providers in the unit. The medical director should intermittently educate the nurses and technicians about the effect of dialysate sodium on the patients and how to pay special attention to the individualized prescription every time that they place the patient on the dialysis machine.

I believe that this strategy would deliver precision medicine, reduce hospitalization, and improve cardiovascular outcomes, eventually leading to economic benefit.