When should Continuous Renal Replacement Therapy (CRRT) be initiated for acidemia?

When to Initiate CRRT for Acidemia

CRRT should be initiated for acidemia when pH falls below 7.15 in patients with metabolic acidosis that is refractory to medical management, especially in hemodynamically unstable patients or those with acute kidney injury.

Indications for CRRT in Acidemia

Primary Indications

• Severe metabolic acidosis with pH < 7.15 that is refractory to medical management 1
• Life-threatening changes in acid-base balance 1
• Hemodynamic instability with acidemia 1
• Acute kidney injury with severe acidemia 1

Clinical Scenarios Warranting CRRT for Acidemia

1. Severe lactic acidosis with hemodynamic compromise

   • When pH < 7.15 with elevated lactate levels
   • When sodium bicarbonate therapy has failed or is contraindicated
   • In patients with metformin-associated lactic acidosis 2

2. Refractory acidemia in septic shock

   • When acidemia persists despite fluid resuscitation and vasopressors
   • When acidemia is contributing to vasopressor resistance 1

3. Acidemia with acute kidney injury

   • When kidney injury limits the body's ability to correct acidosis
   • When other indications for dialysis are also present 1

Decision Algorithm for CRRT Initiation in Acidemia

1. Assess severity of acidemia:

   • Measure arterial pH, serum bicarbonate, anion gap, lactate
   • Calculate base deficit

2. Evaluate response to conventional therapy:

   • Fluid resuscitation
   • Treatment of underlying cause (e.g., sepsis, tissue hypoperfusion)
   • Trial of sodium bicarbonate if pH ≥ 7.15 (note: bicarbonate alone is not recommended for lactic acidosis with pH ≥ 7.15) 1

3. Consider CRRT when:

   • pH remains < 7.15 despite conventional therapy
   • Patient has hemodynamic instability
   • Acidemia is contributing to organ dysfunction
   • Acute kidney injury is present with other indications for RRT

CRRT Implementation for Acidemia

Modality Selection

• Use continuous therapy rather than intermittent for hemodynamically unstable patients 1
• CVVH or CVVHDF are preferred modalities for severe acidemia 1

Buffer Selection

• Use bicarbonate (not lactate) as buffer in dialysate and replacement fluid for patients with:
  • Lactic acidosis 1
  • Liver failure 1
  • Circulatory shock 1

Dosing Considerations

• Deliver an effluent volume of 20-25 mL/kg/h 1
• Higher doses may be required initially for severe acidemia but have not shown improved outcomes 1

Monitoring During CRRT for Acidemia

• Arterial blood gases every 2-4 hours initially
• Serum electrolytes (particularly potassium, phosphate, calcium) every 4-6 hours 3
• If using citrate anticoagulation, monitor:
  • Ionized calcium levels (systemic and post-filter)
  • Acid-base status for citrate accumulation 1

Important Caveats and Pitfalls

• CRRT has limited lactate clearance capacity (approximately 79 mL/min) compared to rates of lactate overproduction in septic shock 4
• Lactic acidosis alone should not be considered a non-renal indication for CRRT 4
• Alkalemia during CRRT can occur and requires monitoring, though it has not been associated with increased mortality 5
• Electrolyte disturbances are common during CRRT and require close monitoring and replacement 3
• Avoid initiating CRRT solely for oliguria or creatinine elevation without other definitive indications 1

Special Considerations

• In patients with hyperammonemia and acidemia, CRRT can effectively reduce ammonia levels 1
• For patients with dysnatremias and acidemia, CRRT allows for controlled correction of sodium abnormalities 6
• In patients with metformin-associated lactic acidosis, CRRT can help with drug removal and acid-base correction 2