How is metabolic alkalosis managed in dialysis patients?

Management of Metabolic Alkalosis in Dialysis Patients

Metabolic alkalosis in dialysis patients should be managed by reducing the dialysate bicarbonate concentration to prevent post-dialysis alkalosis, with target pre-dialysis total CO2 of 19-25 mEq/L and post-dialysis total CO2 ≤29 mEq/L. 1

Pathophysiology and Clinical Context

Metabolic alkalosis in dialysis patients typically results from:

• Excessive bicarbonate delivery during dialysis sessions, particularly when using standard high-bicarbonate dialysate (typically 35-40 mEq/L) 1
• Regional citrate anticoagulation, which delivers large amounts of potential bicarbonate (several hundred mEq) and can cause severe metabolic alkalosis 2, 3
• Vomiting or gastrointestinal losses in patients without kidney function 4

Both metabolic acidosis and alkalosis increase hospitalizations, hemodynamic instability, and mortality in hemodialysis patients 1. The current one-size-fits-all approach leaves many patients either acidotic before or alkalotic after dialysis sessions 1.

Management Algorithm

Step 1: Identify the Cause and Severity

For citrate-induced alkalosis:

• Monitor systemic acid-base balance in patients at high risk for citrate accumulation during continuous renal replacement therapy 2
• Citrate anticoagulation has been associated with both metabolic alkalosis and metabolic acidosis 2

For severe metabolic alkalosis:

• Consider using acid dialysate for rapid correction in severe cases 5, 6
• This involves deliberately using the acid concentrate from a two-part bicarbonate dialysis system 5

Step 2: Adjust Dialysate Bicarbonate Concentration

The primary intervention is individualized dialysate bicarbonate adjustment:

• Target pre-dialysis total CO2: 19-25 mEq/L 1
• Target post-dialysis total CO2: ≤29 mEq/L 1
• Most patients (75%) will require dialysate bicarbonate of 32-34 mEq/L to achieve these targets 1
• This approach eliminates pre-dialysis acidosis and post-dialysis alkalosis in >95% of patients 1

Step 3: Monitor and Adjust

Regular monitoring should include:

• Pre- and post-dialysis total CO2 measurements 1
• Serum calcium, phosphorus, and PTH levels (no clinically significant changes expected with bicarbonate adjustment) 1
• Assessment for intradialytic adverse events 1

Special Considerations for Continuous Renal Replacement Therapy (CRRT)

Buffer selection matters:

• Either lactate or bicarbonate can be used as buffer in most CRRT patients 2
• Bicarbonate is preferred in patients with lactic acidosis and/or liver failure 2
• Bicarbonate is preferred in high-volume hemofiltration 2

Dialysate composition:

• Dialysate or substitution fluid should contain physiologic concentrations of electrolytes, except in patients with extreme imbalances 2
• Avoid supra-physiologic glucose concentrations that result in hyperglycemia 2

Critical Pitfalls to Avoid

Do not use standard high-bicarbonate dialysate for all patients:

• The traditional approach of using 35-40 mEq/L bicarbonate dialysate causes post-dialysis alkalosis in many patients 1
• Only 67.9% of patients are within desired target range at baseline with standard prescriptions 1

Monitor citrate anticoagulation closely:

• Regional citrate anticoagulation can deliver several hundred mEq of potential bicarbonate 3
• Frequent measurements of post-filter and serum-ionized calcium should be performed 2
• Monitoring of systemic acid-base balance is advisable in patients at high risk for citrate accumulation 2

Avoid excessive correction:

• In severe acute acidemia (not alkalosis), overly rapid correction can cause paradoxical CNS acidosis and cerebral edema 7
• The goal is to achieve target ranges, not to overcorrect 1

Treatment Efficacy

Evidence supports individualized bicarbonate adjustment:

• Nearly every patient (>95%) reaches the established target range with individualized dialysate bicarbonate prescription 1
• This approach potentially reduces mortality risk associated with both acidosis and alkalosis 1
• No increase in intradialytic adverse events was observed with this strategy 1