What is the role of bicarbonate (bicarb) in managing acute kidney injury (AKI)?

Role of Bicarbonate in Acute Kidney Injury

Bicarbonate therapy should be reserved for AKI patients with severe metabolic acidosis (pH ≤7.20), particularly those with concurrent acute kidney injury, as it may improve survival in this specific population. 1

Indications for Bicarbonate in AKI

Bicarbonate therapy in AKI should be guided by the following considerations:

Primary Indications

• Severe metabolic acidosis (pH ≤7.20) with concurrent moderate-to-severe AKI 1
• Metabolic acidosis where rapid increase in plasma CO2 content is crucial 2:
  • Cardiac arrest
  • Circulatory insufficiency due to shock or severe dehydration
  • Severe primary lactic acidosis
  • Severe diabetic acidosis

Contraindications/Cautions

• Patients with pH ≥7.15 without life-threatening acidosis 3
• Fluid overloaded patients, where bicarbonate may worsen:
  • Volume overload
  • Pulmonary edema
  • Hypernatremia
  • Hyperosmolarity 3

Evidence-Based Approach to Bicarbonate Use in AKI

For AKI with Severe Acidosis

1. Consider bicarbonate therapy when:

   • pH ≤7.20
   • PaCO₂ ≤45 mm Hg
   • Bicarbonate concentration ≤20 mmol/L
   • Especially with moderate-to-severe AKI 1

2. Administration protocol:

   • Target pH ≥7.30
   • Administer 4.2% sodium bicarbonate infusion
   • Volume of each infusion: 125-250 mL over 30 minutes
   • Maximum 1000 mL within 24 hours 1

For AKI with Renal Replacement Therapy (RRT)

• Use bicarbonate rather than lactate as buffer in dialysate and replacement fluid (2C recommendation) 4
• Strongly recommended to use bicarbonate buffer for patients with:
  • AKI and circulatory shock (1B recommendation) 4
  • AKI and liver failure and/or lactic acidemia (2B recommendation) 4

Clinical Outcomes and Benefits

The most recent high-quality evidence from the BICAR-ICU trial demonstrated:

• In the overall population with severe acidemia: no significant difference in 28-day mortality
• In the subgroup with AKI (AKIN score 2-3): significant improvement in 28-day survival (54% vs 37%, p=0.0283) 1

Potential Adverse Effects

When administering bicarbonate in AKI, monitor for:

• Metabolic alkalosis
• Hypernatremia
• Hypocalcemia 1
• Worsening of pulmonary edema in fluid overloaded patients 3
• Cerebral edema exacerbation 3

Monitoring During Bicarbonate Administration

• Continuous cardiac monitoring
• Frequent electrolyte checks
• Close monitoring of fluid status and respiratory function
• Serial arterial blood gases to assess effectiveness 3

Research Gaps

The KDIGO conference identified the need to further "explore the role for sodium bicarbonate in patients with AKI and metabolic acidosis" as a research priority 4, highlighting that this remains an area requiring additional investigation.

Summary of Approach

1. Assess severity: Determine pH, bicarbonate level, and AKI stage
2. Consider bicarbonate for: pH ≤7.20 with moderate-to-severe AKI
3. Target: pH ≥7.30
4. Monitor: Electrolytes, fluid status, and acid-base balance
5. For RRT: Use bicarbonate-buffered solutions rather than lactate-buffered solutions

While the evidence for bicarbonate therapy in all AKI patients remains limited 5, the most recent high-quality evidence supports its use specifically in patients with severe metabolic acidosis and moderate-to-severe AKI 1.