What will happen if you dialyze a patient with severe metabolic alkalosis using a standard bicarbonate dialysate?

Dialyzing a Patient with Severe Metabolic Alkalosis Using Standard Bicarbonate Dialysate Will Worsen the Alkalosis

Using standard bicarbonate dialysate (typically 32-38 mmol/L) in a patient with severe metabolic alkalosis will exacerbate the alkalosis by adding more bicarbonate to an already alkalemic patient, potentially worsening clinical outcomes including hemodynamic instability, arrhythmias, and neurological complications.

The Core Problem

Standard hemodialysis is inherently an alkalinizing process. When you dialyze against a standard bicarbonate bath (25-38 mmol/L), bicarbonate diffuses from the dialysate into the patient's blood down its concentration gradient. In a patient with severe metabolic alkalosis (pH ≥7.55, bicarbonate >45-55 mmol/L), this creates a dangerous situation where you're adding base to someone who already has too much 1, 2.

What Actually Happens

Immediate Physiological Consequences:

• Further pH elevation: The already elevated arterial pH (>7.55-7.60) will increase further during and immediately after dialysis
• Worsening hypocalcemia: Alkalosis shifts calcium binding to albumin, reducing ionized calcium; standard dialysate exacerbates this 3
• Increased hypokalemia: Alkalosis drives potassium intracellularly; high bicarbonate dialysate worsens this shift 3
• Hemodynamic instability: High dialysate bicarbonate causes greater decreases in stroke volume, cardiac output, and blood pressure compared to low bicarbonate dialysate 3

Clinical Manifestations:

The patient may develop or worsen:

• Cardiac arrhythmias (from alkalosis itself plus electrolyte shifts)
• Neuromuscular complications including seizures and altered mental status
• Myocardial and cerebral ischemia
• Hemodynamic collapse during ultrafiltration 4

The Correct Approach

For severe metabolic alkalosis (pH ≥7.55), you must use LOW bicarbonate dialysate, not standard bicarbonate dialysate 1, 5, 4.

Specific Dialysate Prescription:

1. Use dialysate bicarbonate of 25-28 mmol/L (or even lower if available) rather than standard 32-38 mmol/L 1
2. Some centers have successfully used acetate-based dialysate as an alternative when bicarbonate cannot be lowered sufficiently 6
3. The goal is to create a reverse gradient where bicarbonate moves FROM the patient INTO the dialysate

Monitoring During Treatment:

• Arterial blood gases every 1-2 hours initially
• Ionized calcium levels (not just total calcium) 7
• Serum potassium closely
• Continuous cardiac monitoring for arrhythmias 8
• Blood pressure and hemodynamic parameters

Evidence-Based Rationale

The 2002 International Consensus Conference on CRRT established that bicarbonate is preferred over lactate as a buffer in dialysate for most patients 7. However, this recommendation assumes normal or acidotic patients. The same guidelines note that citrate anticoagulation can cause metabolic alkalosis 7, implicitly acknowledging that base administration during dialysis affects acid-base status.

More recent evidence from 2024 demonstrates that high dialysate bicarbonate (38 mmol/L) causes transient metabolic alkalosis even in normal patients, with associated hemodynamic instability, hypocalcemia, and hypokalemia 3. In patients starting with severe alkalosis, this effect is magnified dangerously.

Case reports consistently show that conventional hemodialysis with NORMAL (not high) bicarbonate dialysate (25-28 mmol/L) successfully and safely reverses severe metabolic alkalosis 1, 5. One series reported three cases with pH >7.60 and bicarbonate >55 mmol/L where standard dialysate with 25-28 mmol/L bicarbonate "reversed quickly and safely" the extreme alkalosis 1.

Critical Pitfalls to Avoid

1. Don't assume "standard" is safe: Standard dialysate is designed for typical ESRD patients who tend toward acidosis, not alkalosis
2. Don't rely on ultrafiltration alone: While removing volume helps with contraction alkalosis, it doesn't remove the excess bicarbonate effectively
3. Don't forget the underlying cause: Address gastric losses (H2 blockers or PPIs), stop diuretics if possible, correct hypokalemia 1, 5
4. Don't dialyze too aggressively: Rapid shifts in pH can be as dangerous as the alkalosis itself

Special Considerations

In patients with oliguric or anuric renal failure, the normal compensatory mechanism of urinary bicarbonate excretion is lost 1, 2. This makes dialysis the only effective route for bicarbonate removal. The combination of gastric acid loss (vomiting, NG suction) plus inability to excrete bicarbonate renally creates the perfect storm for severe, refractory alkalosis 1.

For continuous renal replacement therapy (CRRT), the same principle applies: use replacement/dialysate fluids with lower bicarbonate concentrations (20-25 mmol/L rather than standard 32-35 mmol/L) 7, 4.

Bottom Line Algorithm

If pH ≥7.55 or bicarbonate >45 mmol/L:

1. Use LOW bicarbonate dialysate (25-28 mmol/L maximum)
2. Monitor ABGs hourly initially
3. Watch ionized calcium and potassium closely
4. Treat underlying cause (stop gastric losses, give PPIs)
5. Consider acetate dialysate if low bicarbonate unavailable

Never use standard (32-38 mmol/L) or high (>38 mmol/L) bicarbonate dialysate in severe metabolic alkalosis—you will make the patient worse.