What are the guidelines for initiating Continuous Renal Replacement Therapy (CRRT) in patients with impaired renal function?

CRRT Initiation Guidelines for Impaired Renal Function

Initiate CRRT emergently when life-threatening metabolic derangements are present, and preferentially use CRRT over intermittent hemodialysis for hemodynamically unstable patients with acute kidney injury. 1

Absolute Indications for Emergency CRRT Initiation

Start CRRT immediately when any of these life-threatening conditions exist 1:

• Severe hyperkalemia unresponsive to medical management
• Refractory metabolic acidosis threatening cardiovascular stability
• Diuretic-unresponsive pulmonary edema causing respiratory compromise
• Uremic complications (pericarditis, encephalopathy, bleeding)
• Severe volume overload in hemodynamically unstable patients

The 2020 KDIGO conference emphasized that RRT should be initiated when metabolic and fluid demands exceed kidney capacity, rather than waiting for arbitrary laboratory thresholds 1. This represents a shift from rigid BUN/creatinine cutoffs to dynamic clinical assessment.

Patient Selection Criteria for CRRT vs. Intermittent Hemodialysis

Choose CRRT preferentially for 1, 2:

• Hemodynamically unstable patients requiring vasopressor support (Grade 2B evidence)
• Acute brain injury or increased intracranial pressure - CRRT causes less ICP fluctuation than intermittent modalities 1
• Septic shock, ARDS, or severe burns where continuous inflammatory mediator removal may be beneficial 1, 2
• Patients requiring continuous fluid removal who cannot tolerate rapid fluid shifts 2, 3

The evidence shows CRRT provides superior hemodynamic stability through gradual fluid and solute shifts, though randomized trials have not demonstrated mortality benefit over intermittent hemodialysis 1. The key advantage is physiologic tolerance, not survival improvement.

Technical Setup Requirements

Vascular Access Selection

Follow this strict hierarchy for catheter placement 1, 2, 3:

1. First choice: Right internal jugular vein - optimal flow and lowest complication risk
2. Second choice: Femoral vein (inferior in obese patients)
3. Third choice: Left internal jugular vein
4. Last resort: Subclavian vein (dominant side preferred) - avoid due to thrombosis/stenosis risk

Always use ultrasound guidance for insertion (Grade 1A evidence) 1, 2. Obtain chest radiograph before first use of jugular or subclavian catheters 1, 2.

Use uncuffed nontunneled catheters for acute initiation; reserve cuffed catheters only for expected prolonged RRT needs 1, 2.

Anticoagulation Strategy

Regional citrate anticoagulation is first-line for patients without contraindications (Grade 2C evidence) 1, 2, 3. This provides superior filter life compared to heparin while reducing bleeding risk.

Avoid heparin-based anticoagulation in patients with increased bleeding risk 1. For heparin-induced thrombocytopenia, use direct thrombin inhibitors (argatroban preferred if no severe liver failure) or Factor Xa inhibitors (Grade 1A evidence) 1, 2.

Dialysate and Replacement Fluid Composition

Use bicarbonate-buffered solutions exclusively rather than lactate-buffered fluids 1, 2, 3:

• Grade 1B evidence for patients with circulatory shock (impaired lactate metabolism)
• Grade 2B evidence for liver failure or lactic acidemia patients
• Grade 2C evidence for all other AKI patients

All fluids must meet AAMI standards for bacterial and endotoxin contamination (Grade 1B evidence) 1, 2.

Use biocompatible membrane dialyzers to reduce inflammatory activation (Grade 2C evidence) 1, 2, 3.

CRRT Dosing Prescription

Deliver 20-25 mL/kg/hour effluent volume for CRRT in AKI (Grade 1A evidence) 1, 2, 3. This typically requires prescribing higher volumes to account for downtime and circuit issues.

Monitor actual delivered dose frequently and adjust prescription accordingly (Grade 1B evidence) 1, 2. The prescribed dose must be documented before each session, with systematic tracking of delivered versus prescribed dose as a quality metric 3.

Higher doses beyond 25 mL/kg/hour have not shown mortality benefit in randomized trials and should not be routinely used 1.

Special Considerations and Common Pitfalls

Do not rely on BUN or creatinine thresholds alone for initiation timing 1, 2. The rate of azotemia increase is more clinically relevant than absolute values 1.

Avoid lactate-buffered solutions in liver failure patients - they cannot metabolize lactate and risk worsening acidosis 1, 2, 4. Use bicarbonate exclusively in this population.

Monitor for significant nutrient losses during CRRT, including 10-15g amino acids daily, water-soluble vitamins, phosphate, and magnesium 3, 4. Patients on CRRT require higher protein intake (1.5-1.7 g/kg/day) 3.

In liver failure with citrate anticoagulation, monitor ionized calcium levels and total calcium to ionized calcium ratio intensively, as impaired citrate metabolism can cause citrate accumulation 4.

Avoid subclavian access whenever possible due to high thrombosis risk and potential for future dialysis access complications 2, 4.

Discontinuation Criteria

Stop CRRT when 1:

• Kidney function has adequately recovered
• Patient becomes hemodynamically stable enough to transition to intermittent hemodialysis
• Vasopressor support has been discontinued
• Intracranial hypertension has resolved
• RRT becomes inconsistent with goals of care

Transition from CRRT to intermittent modalities should occur when the clinical conditions that necessitated continuous therapy have resolved 1.