When should Continuous Renal Replacement Therapy (CRRT) be initiated in patients with impaired renal function?

When to Start Continuous Renal Replacement Therapy (CRRT)

CRRT should be initiated emergently when life-threatening changes in fluid, electrolyte, and acid-base balance exist, rather than waiting for specific BUN or creatinine thresholds. 1

Primary Indications for CRRT Initiation

• Emergent/Life-threatening conditions requiring immediate intervention: 1

  • Severe hyperkalemia refractory to medical management
  • Severe metabolic acidosis not responding to conventional treatment
  • Pulmonary edema/volume overload unresponsive to diuretics
  • Uremic complications (encephalopathy, pericarditis)

• Hemodynamic instability making conventional intermittent hemodialysis unsuitable 1, 2

  • Patients requiring vasopressor support
  • Patients with cardiovascular instability
  • Patients with shock states (particularly septic shock)

• Specific clinical scenarios where CRRT offers advantages: 2

  • Patients with or at risk for cerebral edema
  • Patients with acute respiratory distress syndrome (ARDS)
  • Patients with severe burns requiring fluid management
  • Patients with multi-organ failure requiring precise fluid balance

Decision-Making Framework

When considering CRRT initiation, evaluate:

1. Clinical context beyond single laboratory values 1

   • Trends in laboratory values rather than absolute thresholds
   • Overall clinical trajectory of the patient
   • Presence of conditions that can be modified with CRRT

2. Demand vs. capacity assessment 1

   • Whether metabolic and fluid demands exceed the kidney's capacity
   • Progression of AKI despite conservative management
   • Fluid accumulation despite diuretic therapy

3. Risk-benefit evaluation 1, 2

   • For transplant candidates, CRRT may serve as a bridge to transplantation
   • For non-transplant candidates, individualized risk assessment based on illness severity

Special Considerations

• In hepatorenal syndrome (HRS): CRRT is preferred when patients are hemodynamically unstable and have failed medical management with vasoconstrictors and albumin 1

• In patients with increased intracranial pressure: CRRT is preferred over intermittent hemodialysis due to lower risk of increasing intracranial pressure 1, 2

• For fluid management: When precise control of fluid balance is required, especially in patients with ARDS or burns 2, 3

Common Pitfalls to Avoid

• Delaying CRRT initiation until extreme uremia develops can worsen outcomes 1, 2

• Relying solely on BUN/creatinine thresholds rather than considering the broader clinical picture 1

• Failing to consider hemodynamic status when selecting between CRRT and intermittent modalities 2, 3

• Underestimating the importance of access placement - right jugular or femoral veins are preferred sites for catheter placement 1, 2

• Inadequate anticoagulation strategy - regional citrate anticoagulation is preferred for patients without contraindications 1, 2

Technical Aspects When Starting CRRT

• Vascular access: Use uncuffed non-tunneled dialysis catheters with preferred sites being right jugular vein, femoral vein, left jugular vein, and subclavian vein (in that order) 1, 2

• Anticoagulation: Regional citrate is first-line for patients without contraindications; unfractionated or low-molecular-weight heparin for those with citrate contraindications 1, 2

• Dosing: Deliver an effluent volume of 20-25 mL/kg/h, which typically requires a higher prescription to account for treatment interruptions 1, 2

• Modality selection: CVVH, CVVHD, or CVVHDF based on specific patient needs and institutional expertise 2, 4

While there remains controversy regarding the optimal timing of CRRT initiation in the absence of life-threatening indications, the evidence suggests that earlier intervention before severe complications develop may be beneficial for patient outcomes, particularly regarding mortality and quality of life 1.