Should bicarbonate (bicarb) in the dialysate be adjusted up or down for a patient with metabolic acidosis on hemodialysis?

Bicarbonate in Dialysate Should Be Adjusted UP for Metabolic Acidosis

For hemodialysis patients with metabolic acidosis, the dialysate bicarbonate concentration should be increased to achieve and maintain a predialysis serum bicarbonate ≥22 mmol/L. 1

Target Bicarbonate Levels

• The evidence-based target is predialysis serum bicarbonate ≥22 mmol/L, which prevents bone disease, protein catabolism, and progression of metabolic derangements. 1
• Patients with normal bone biopsy results have serum bicarbonate levels around 23 mmol/L, while those with osteodystrophy have levels below 20 mmol/L. 1
• Serum bicarbonate should be measured at least monthly to guide dialysate adjustments. 1

Mechanism and Rationale

• Hemodialysis is an intermittent therapy, making acidosis correction challenging with fixed dialysate bicarbonate concentrations. 2
• The dialysate bicarbonate concentration directly determines the delivered bicarbonate dose during each treatment session. 3
• Approximately 30% of hemodialysis patients have metabolic acidosis (bicarbonate <22 mEq/L) with standard dialysate concentrations. 4

Practical Implementation

• Most patients require dialysate bicarbonate concentrations of 32-34 mEq/L to achieve target predialysis bicarbonate levels. 5
• Individualized adjustment based on pre- and post-dialysis total CO2 measurements (target: pre-dialysis 19-25 mEq/L, post-dialysis ≤29 mEq/L) eliminates both predialysis acidosis and post-dialysis alkalosis. 5
• Increasing dialysate bicarbonate from 35 to 39 mmol/L significantly improves serum bicarbonate from 21.7 to 23.1-23.3 mmol/L within 3-6 months. 3

Clinical Consequences of Untreated Acidosis

• Bone disease: Acidosis exaggerates bone dissolution by altering calcium-PTH-vitamin D homeostasis, contributing to renal osteodystrophy and increased fracture risk. 1
• Protein catabolism: Increased protein breakdown leads to muscle wasting, malnutrition, and negative nitrogen balance. 1, 6
• Secondary hyperparathyroidism: Dialysis patients with acidosis show progression of secondary hyperparathyroidism over 18 months. 1
• Increased mortality: Both metabolic acidosis and alkalosis increase hospitalizations, hemodynamic instability, and mortality in hemodialysis patients. 5

Key Determinants to Address

Beyond dialysate adjustment, three factors independently affect metabolic acidosis in hemodialysis patients:

• Protein breakdown (increased protein nitrogen appearance worsens acidosis; OR 1.60 per 0.2 g/kg/day). 4
• Dialysis dose (increased Kt/V improves acidosis; OR 0.61 per 0.20 increase). 4
• Phosphorus binders (calcium carbonate use improves acidosis; OR 0.38 per 2 g/day). 4

Critical Pitfall to Avoid

Never use citrate-containing alkali supplements in dialysis patients exposed to aluminum salts, as citrate increases aluminum absorption both before and during dialysis, potentially worsening bone disease. 1 This is particularly important when considering oral bicarbonate supplementation as an adjunct to dialysate adjustment.

Monitoring During Adjustment

• Calcium, phosphate, PTH, sodium, and potassium levels remain clinically stable with dialysate bicarbonate adjustments. 5
• No increase in intradialytic adverse events occurs with higher dialysate bicarbonate concentrations. 5
• Serum bicarbonate shows inverse correlation with protein catabolic rate (nPCR), which decreases as acidosis is corrected. 3