How to maintain acid-base balance in a Chronic Kidney Disease (CKD) 5 patient on hemodialysis?

Maintaining Acid-Base Balance in CKD Stage 5 Patients on Hemodialysis

In CKD Stage 5 hemodialysis patients, maintain acid-base balance by targeting serum bicarbonate levels of 24-26 mmol/L through individualized dialysate bicarbonate concentration (typically 32-34 mEq/L) and supplemental oral sodium bicarbonate when needed. 1

Primary Strategy: Dialysate Bicarbonate Optimization

The cornerstone of acid-base management is adjusting the dialysate bicarbonate concentration based on pre- and post-dialysis measurements. 2, 3

Target Bicarbonate Levels

• Pre-dialysis serum bicarbonate: 19-25 mEq/L 2
• Post-dialysis total CO2: ≤29 mEq/L 2
• Optimal maintenance range: 24-26 mmol/L 1

Dialysate Bicarbonate Prescription

• Most patients require dialysate bicarbonate of 32-34 mEq/L to achieve target ranges 2
• Higher dialysate bicarbonate concentrations (38 mmol/L) can safely increase predialysis serum bicarbonate when standard concentrations are insufficient 1
• Avoid one-size-fits-all approach: individualize based on monthly pre- and post-dialysis measurements 2

Supplemental Oral Bicarbonate Therapy

When dialysate adjustment alone is insufficient, add oral sodium bicarbonate 0.5-1 mEq/kg/day (typically 2-4 g/day or 25-50 mEq/day) to reach target bicarbonate levels. 1, 4

Indications for Oral Supplementation

• Pre-dialysis bicarbonate persistently <19 mEq/L despite optimized dialysate 5
• Patients requiring higher bicarbonate delivery than dialysate alone can provide 1
• Goal: serum bicarbonate 22-24 mmol/L minimum 4

Monitoring Protocol

Measure serum bicarbonate monthly in all maintenance hemodialysis patients. 1

When to Measure Arterial Blood Gases

• If uncertainty exists about severity of acidemia 1
• When serum bicarbonate <19 mEq/L to assess pH directly 5
• If symptoms suggest severe metabolic acidosis 4

Critical Pitfalls to Avoid

Phosphate Binder Considerations

If using sevelamer as phosphate binder, monitor acidosis more closely as it aggravates metabolic acidosis by favoring endogenous acid production. 4 Consider switching to calcium-based binders or increasing bicarbonate supplementation.

Calcium Correction First

Always correct hypocalcemia before treating metabolic acidosis in CKD patients, as bicarbonate administration can worsen hypocalcemia. 4

Post-Dialysis Alkalosis

Avoid excessive dialysate bicarbonate that causes post-dialysis total CO2 >29 mEq/L, as both acidosis and alkalosis increase hospitalizations and mortality. 2

Sodium Load Consideration

When prescribing oral sodium bicarbonate, account for the sodium content (approximately 1 g sodium per 4 g sodium bicarbonate) toward the patient's total sodium restriction of <2.3 g/day. 1, 6

Consequences of Untreated Acidosis

Metabolic acidosis in hemodialysis patients causes:

• Increased protein degradation and decreased albumin synthesis 1
• Bone demineralization through release of calcium and phosphate 4
• Muscle weakness and atrophy 4
• Increased mortality risk 7, 2
• Accelerated progression of residual kidney function loss 1

Dietary Adjuncts

Limit protein intake to <1 g/kg/day to reduce endogenous acid production, though this must be balanced against the need for adequate protein (1.2 g/kg/day) in hemodialysis patients. 4, 1 The bicarbonate supplementation strategy takes precedence over protein restriction in dialysis patients.

Algorithm for Implementation

1. Measure pre- and post-dialysis bicarbonate monthly 1
2. If pre-dialysis bicarbonate 19-25 mEq/L and post-dialysis ≤29 mEq/L: continue current dialysate 2
3. If pre-dialysis bicarbonate <19 mEq/L: increase dialysate bicarbonate by 2-4 mEq/L increments 2
4. If post-dialysis bicarbonate >29 mEq/L: decrease dialysate bicarbonate by 2 mEq/L 2
5. If dialysate optimization insufficient: add oral sodium bicarbonate 0.5-1 mEq/kg/day 1, 4
6. Recheck bicarbonate in 2-4 weeks after any adjustment 2