Indications for Continuous Renal Replacement Therapy (CRRT)
CRRT should be initiated emergently when life-threatening changes in fluid, electrolyte, and acid-base balance exist in patients with acute kidney injury. 1, 2
Absolute (Emergent) Indications
CRRT must be started immediately for the following life-threatening conditions 2:
- Severe hyperkalemia with ECG changes or rapidly rising potassium levels refractory to medical management 2
- Pulmonary edema or severe fluid overload causing respiratory compromise unresponsive to diuretics 2, 3
- Uremic complications including encephalopathy, pericarditis, or bleeding 2
- Severe metabolic acidosis with impaired respiratory compensation 2
- Severe symptomatic dysnatremia resistant to medical management 2
Relative Indications (Clinical Context-Dependent)
Beyond emergent situations, CRRT initiation should consider the broader clinical context and trends in laboratory values rather than single BUN and creatinine thresholds alone 1. The following clinical scenarios favor CRRT:
Hemodynamic Instability
CRRT is preferred over intermittent hemodialysis for hemodynamically unstable patients requiring vasopressor support 1, 2, 3. This recommendation carries a 2B grade, reflecting moderate-quality evidence that CRRT provides superior hemodynamic tolerance compared to intermittent modalities 3.
Neurological Considerations
CRRT should be used rather than intermittent RRT for patients with acute brain injury, increased intracranial pressure, or generalized brain edema 1, 2, 3. CRRT minimizes cerebral edema risk and intracranial pressure fluctuations that can occur with intermittent hemodialysis 3.
Fluid Management
CRRT is indicated when severe fluid overload cannot be adequately controlled by intermittent hemodialysis, particularly in critically ill cardiac patients where positive fluid balance management is crucial 2, 3.
Extracorporeal Life Support
For patients requiring ECMO or other extracorporeal life support, CRRT should be integrated to prevent and manage fluid overload 2, 3, 4. This is critical for optimal ECMO function 3.
Technical Specifications When CRRT is Initiated
Once the decision to start CRRT is made, specific technical parameters must be followed:
Dosing
Deliver an effluent volume of 20-25 mL/kg/hour for CRRT in AKI 1, 2, 3, 4. This is a grade 1A recommendation. The prescription should be higher than this target to account for downtime 1.
Buffer Selection
Use bicarbonate rather than lactate as the buffer in dialysate and replacement fluid 1, 2, 3, 4. This is particularly important (grade 1B recommendation) for patients with circulatory shock, liver failure, or lactic acidemia 1, 3, 4.
Anticoagulation
For patients without increased bleeding risk, regional citrate anticoagulation is preferred over heparin 1, 3, 4. This carries a 2B grade recommendation 1.
Vascular Access
Use an uncuffed nontunneled dialysis catheter with the following site preferences 1, 3, 4:
- First choice: Right jugular vein 1, 3
- Second choice: Femoral vein 1, 3
- Third choice: Left jugular vein 1, 3
- Last choice: Subclavian vein (avoid due to stenosis risk) 1, 3, 4
Always use ultrasound guidance for catheter insertion (grade 1A) 1, 3.
Common Pitfalls to Avoid
Do not rely solely on absolute BUN or creatinine values to trigger CRRT initiation 1, 3. A Canadian survey revealed substantial variability in practice, with 57-59% of physicians influenced by absolute creatinine and urea values, but this approach lacks evidence support 1.
Avoid subclavian vein access due to increased risk of thrombosis and stenosis with large nontunneled catheters 1, 3, 4.
Do not use lactate-buffered solutions in patients with liver failure or lactic acidosis 1, 3, 4, as these patients cannot metabolize lactate effectively.
When to Transition from CRRT
Consider transitioning from CRRT to intermittent hemodialysis when all of the following are met 3, 4:
- Vasopressor support has been discontinued 3
- Hemodynamic stability has been achieved 3
- Intracranial hypertension has resolved (if applicable) 3
- Fluid balance can be adequately controlled by intermittent hemodialysis 3
Discontinuation of RRT
Discontinue RRT when intrinsic kidney function has recovered to adequately meet patient needs, or when RRT is no longer consistent with goals of care 1. Kidney recovery is defined as sustained independence from RRT for a minimum of 14 days 2.