When should Continuous Renal Replacement Therapy (CRRT) be ordered versus Intermittent Hemodialysis (iHD)?

When to Choose CRRT vs IHD for Renal Replacement Therapy

CRRT should be used over intermittent hemodialysis (IHD) for patients with hemodynamic instability and those with acute brain injury or increased intracranial pressure, while IHD can be used for hemodynamically stable patients without risk of cerebral edema. 1, 2

Primary Indications for CRRT

• Hemodynamic instability: CRRT is the preferred modality for patients with AKI who are hemodynamically unstable due to its gradual and continuous nature, which provides better cardiovascular stability 1, 2
• Cerebral edema risk: CRRT is recommended for patients with acute brain injury or other causes of increased intracranial pressure or generalized brain edema 1, 2
• Severe volume overload: Patients requiring continuous and controlled fluid removal benefit from CRRT's ability to provide steady ultrafiltration 2, 1
• Severe acid-base disturbances: CRRT allows for continuous correction of metabolic derangements without rapid shifts 2, 3
• Critical illness with multiple organ failure: Patients with septic shock, ARDS, or burns may benefit from continuous removal of inflammatory mediators 1, 2

Primary Indications for IHD

• Hemodynamically stable patients: IHD is appropriate for patients with stable blood pressure who can tolerate more rapid fluid and solute removal 1, 4
• Patients without cerebral edema risk: Those without acute brain injury or increased intracranial pressure 1
• Less severe illness: Patients with lower SOFA scores (3-10) may have better outcomes with IHD compared to CRRT 4
• Need for intermittent therapy: Patients who would benefit from periods off dialysis (e.g., for mobility, procedures) 2, 1

Decision Algorithm for RRT Modality Selection

1. Assess hemodynamic stability:

   • Hypotension or vasopressor requirement → CRRT 1, 2
   • Stable blood pressure without vasopressors → Consider IHD 1, 4

2. Evaluate neurological status:

   • Acute brain injury, increased ICP, or risk of cerebral edema → CRRT 1, 2
   • No neurological concerns → Either modality appropriate 1

3. Consider fluid management needs:

   • Severe volume overload requiring precise and gradual removal → CRRT 2
   • Less severe fluid overload that can be managed intermittently → IHD 1

4. Assess metabolic derangements:

   • Severe acid-base disturbances requiring continuous correction → CRRT 2, 3
   • Mild to moderate metabolic abnormalities → Either modality 1

5. Evaluate overall illness severity:

   • High SOFA scores with multiple organ dysfunction → CRRT 2, 1
   • Lower SOFA scores (3-10) with fewer complications → Consider IHD 4

Technical Considerations

• CRRT delivery:

  • Recommended effluent volume is 20-25 mL/kg/h for CRRT in AKI 1, 2
  • Bicarbonate is preferred over lactate as buffer, especially for patients with shock, liver failure, or lactic acidemia 1, 2
  • Regional citrate anticoagulation is preferred for patients without contraindications 1, 5

• IHD delivery:

  • Recommended Kt/V of 3.9 per week when using intermittent RRT in AKI 1
  • Biocompatible membranes should be used for both modalities 1, 2

Common Pitfalls and Considerations

• Avoid subclavian vein access due to risk of thrombosis and stenosis; prefer right jugular vein as first choice 1, 2
• Don't rely solely on BUN/creatinine thresholds for initiating RRT; consider broader clinical context 2, 5
• Monitor for electrolyte complications with CRRT, particularly hypophosphatemia and hypokalemia, which may require supplementation in replacement fluids 3, 6
• Consider that CRRT may not provide mortality benefit despite theoretical advantages; some studies suggest IHD may be non-inferior or even superior in less severely ill patients 4
• Be aware of resource implications: CRRT requires specialized equipment, continuous nursing care, and is generally more costly than IHD 7

Special Considerations

• For patients with liver failure, avoid lactate-buffered solutions during CRRT and use bicarbonate instead 1, 2
• For patients with dysnatremias, CRRT allows for more gradual correction of sodium abnormalities, reducing risk of osmotic demyelination syndrome 6
• For patients with heparin-induced thrombocytopenia, use direct thrombin inhibitors or Factor Xa inhibitors during RRT 1, 5

Remember that CRRT and IHD should be viewed as complementary therapies rather than competing options, with selection based on individual patient characteristics and clinical circumstances 1, 2.