Potassium Dialysate Concentrations: Clinical Insights for Dietitians

What is the best potassium dialysate concentration (K bath) for my patient?

One of the key challenges for people who are receiving hemodialysis therapy is maintaining serum potassium values within homeostatic ranges.  And one of the key strategies that can be used to help is the choosing the right potassium dialysate concentration. (The potassium dialysate concentration is often called the “bath”, so it is not uncommon for people to call it the K-bath.) In my clinical practice, I have come across the potassium dialysate concentrations listed in table 1.

Table 1: Common Potassium Dialysate Concentrations (Potassium Baths) and their impact on serum potassium

The key reference for today’s post comes from: Pun, Patrick H., and John P. Middleton. “Dialysate potassium, dialysate magnesium, and hemodialysis risk.” Journal of the American Society of Nephrology 28.12 (2017): 3441-3451.

Is it harmful to remove too much potassium during dialysis?

Rapid potassium removal during dialysis can cause acute shifts, potentially leading to muscle paralysis and fatal arrhythmias. Notably, the highest risk of cardiac events occurs on the dialysis day that falls after the two-day “weekend” gap.

Over time, many dialysis units have discontinued use of the lowest potassium dialysis concentration baths (the K0) and less frequently use K1 baths due to these risks.

What are the goals for potassium management for those on hemodialysis?

1. Prevent serious hyperkalemia by removing potassium that accumulates between dialysis sessions
2. Avoid hypokalemia during or after the session

How much potassium is removed during hemodialysis?

Each session removes approximately 70–100 mEq of potassium, or 2,730–3,900 mg (based on 1 mEq = 39 mg). Over three weekly sessions, this equates to 8,190–11,700 mg of potassium.

Do we remove enough potassium during dialysis?

According to a 2011 study using the 2007 Canadian Community Health Survey, the amount of potassium consumed by Canadian adults is shown in the table below.

However, these gaps may overestimate potassium burden due to fecal excretion and differences in bioavailability. Still, many patients likely remain in positive potassium balance.

What affects potassium removal during dialysis?

• Gradient Difference: This is the primary driver. The gradient differences describes the difference between serum potassium and the potassium dialysate concentration. The larger the difference between the serum and dialysate the more potassium is removed.
• Dialysate Glucose: High dialysate glucose promotes potassium shift into serum and out of the cell, enhancing removal.
• Ultrafiltration: Accounts for ~6% of potassium removal via convective clearance.

Dialysate Bicarbonate: While higher bicarbonate shifts potassium intracellularly, lowering serum levels dialysate bicarbonate concentration does not change potassium removal.

How Do Serum Potassium Levels Change During and After Dialysis?

I loved this figure from the article that graphed how the potassium levels were changing depending on the serum potassium level at the start of the dialysis session.

Notice from this figure that:

• The largest drop occurs in the first hour.
• The higher initial serum potassium (solid black line) resulted in a faster decline and a stronger rebound post-HD.
• The smaller concentration difference (the dotted line) led to a more gradual change with less rebound.

What is the Ideal Pre-Dialysis Potassium Level?

Several studies have investigated what level of potassium drawn at the beginning of the dialysis run is associated with the lowest mortality:

• One study (n=2134): Ideal = 5.1 mEq/L, as levels increased so did the risk
• Another (n>81,000): 4.6–5.3 mmol/L had lowest mortality
• A third (n=55,000): 4.0–5.5 mmol/L lowest risk

Together, these suggest that pre-dialysis potassium values between 5.0–5.5 mmol/L may be acceptable for many patients.

Is Post-Dialysis Potassium Monitoring Useful?

While its prognostic value is unclear, it may help assess patients at risk for post-dialysis arrhythmias.

Are low potassium dialysis concentrations (low K baths) safe?

The answer to this question may depend on where you are in the world. The Use of <2 mEq/L baths is rare in the U.S. (~3%) but common in Spain (62%). However, there is general consensus that baths <2mEq/L are associated with increased risk, especially in patients starting HD with normal or low potassium levels.

But what about low K baths for people who start HD with hyperkalemia? Here the evidence is less clear. No study has shown a significant risk of clinical events (such as sudden cardiac death) associated with low-potassium dialysate among patients with pre-dialysis serum potassium values at or above 5. However, studies using cardiac monitoring devices have consistently reported increase risk of changes in electrocardiographic conduction when K0 or K1 baths are used. This suggests that better studies are needed to help us understand the impacts of low K baths on people who have hyperkalemia.

Are high potassium dialysis concentrations (High K baths) safe?

Most people would define potassium dialysate concentrations above 3mEq/L as a high K bath.

• In a study of >81000 people receiving HD in the US, K baths ≥3 mEq/L were linked to higher mortality among patients with serum potassium ≥5 mmol/L.
• Another study also reported a higher risk of mortality with high K baths, though when malnutrition and inflammation were considered, the risk reduced. (I would add that this finding makes sense to me, often it is my patients who aren’t eating that are dialyzing against the higher K baths).

Clinical Takeaways

• Avoid potassium baths <2 mEq/L in patients with pre-dialysis potassium <5 mmol/L.
• Consider individual potassium values when choosing dialysate baths—higher or lower values may justify deviations.
• Tailor K bath prescriptions using regular serum potassium monitoring.

If you want to know more about hyperkalemia management – check out my other blog posts on the topic here and don’t forget to use my hyperkalemia management cheat sheet which can be found in the dietitians only section of my website.