What is the recommended treatment approach for patients requiring renal replacement therapy, specifically Continuous Renal Replacement Therapy (CRRT)?

Continuous Renal Replacement Therapy (CRRT) Treatment Approach

Indications for CRRT

CRRT should be used preferentially over intermittent hemodialysis in hemodynamically unstable patients with acute kidney injury requiring vasopressor support. 1

Specific Clinical Scenarios Requiring CRRT:

• Hemodynamic instability: Patients requiring vasopressor support cannot tolerate the rapid fluid and solute shifts of intermittent hemodialysis 1, 2
• Acute brain injury or increased intracranial pressure: The slower solute flux with CRRT prevents rapid osmotic shifts that can worsen cerebral edema 1, 2
• Severe fluid overload: When continuous volume removal is needed and intermittent modalities are inadequate 2, 3
• Patients on ECMO or extracorporeal life support: CRRT integrates well with these circuits 2, 3

Absolute Indications for Initiating RRT (Apply to Both CRRT and Intermittent):

• Diuretic-unresponsive pulmonary edema 1, 4
• Severe hyperkalemia (K+ >6.5 mEq/L or ECG changes) unresponsive to medical management 4
• Severe metabolic acidosis (pH <7.1) refractory to bicarbonate 4
• Uremic complications (pericarditis, encephalopathy, bleeding) 1, 4

Critical pitfall: Do not wait for specific BUN or creatinine thresholds; initiate RRT before life-threatening complications develop in critically ill patients, as consequences are more severe than in chronic kidney disease patients 1, 4

CRRT Modality Selection

Continuous venovenous hemodiafiltration (CVVHDF) is the preferred CRRT modality as it combines both convective and diffusive clearance. 2, 3

Alternative Modalities:

• CVVH (continuous venovenous hemofiltration): Uses primarily convective clearance; acceptable alternative to CVVHDF 2, 3
• CVVHD (continuous venovenous hemodialysis): Uses primarily diffusive clearance 3

The choice between these modalities should be based on institutional expertise and available resources, as all are acceptable 2

Vascular Access

Use an uncuffed nontunneled dialysis catheter for initiating CRRT in AKI patients. 1, 3

Vein Selection Algorithm (in order of preference):

1. First choice: Right internal jugular vein 1, 2, 3
2. Second choice: Femoral vein (note: inferior in obese patients) 1, 2, 3
3. Third choice: Left internal jugular vein 1, 2, 3
4. Last choice (avoid): Subclavian vein—high risk of thrombosis and stenosis that can compromise future permanent access 2, 3

Catheter Insertion Requirements:

• Mandatory: Use ultrasound guidance for all catheter insertions 1, 3
• Mandatory: Obtain chest radiograph after internal jugular or subclavian placement before first use 1, 3
• Avoid: Topical antibiotics at insertion site 1
• Avoid: Antibiotic locks for infection prevention 1

Anticoagulation Strategy

Regional citrate anticoagulation is the first-line choice for patients without contraindications to citrate. 1, 3, 5

Anticoagulation Algorithm:

For patients WITHOUT increased bleeding risk:

• Use regional citrate anticoagulation 1, 3, 5

For patients WITH increased bleeding risk:

• First choice: Regional citrate anticoagulation (if no citrate contraindications) 1
• Avoid regional heparinization 1

For patients with heparin-induced thrombocytopenia (HIT):

• Stop all heparin immediately 1
• Use direct thrombin inhibitors (argatroban) or Factor Xa inhibitors (danaparoid, fondaparinux) 1, 3
• If no severe liver failure: prefer argatroban over other agents 1

Critical caveat: In the United States, FDA-approved citrate solutions for regional anticoagulation during CRRT are not available, limiting this recommendation's applicability 1

CRRT Dosing

Deliver an effluent volume of 20-25 mL/kg/hour for CRRT in AKI. 1, 2, 3, 6, 5

Dosing Implementation:

• Prescribe a higher effluent volume than the target 20-25 mL/kg/hour to account for downtime (procedures, filter changes, etc.) 1
• Frequently assess the actual delivered dose and adjust prescription accordingly 1, 3
• The dose should achieve goals of electrolyte balance, acid-base correction, solute clearance, and fluid balance 1, 3

Important note: Higher doses (>40 mL/kg/hour) do not improve mortality and are not recommended 5

Dialysate and Replacement Fluid Composition

Use bicarbonate-based (not lactate-based) solutions as the buffer in dialysate and replacement fluids. 1, 2, 3

Specific Clinical Scenarios Requiring Bicarbonate:

• Mandatory for: Patients with circulatory shock 1, 3
• Mandatory for: Patients with liver failure 1, 3
• Mandatory for: Patients with lactic acidemia 1, 3
• Suggested for: All other AKI patients 1

Fluid Quality Standards:

• All fluids must comply with American Association of Medical Instrumentation (AAMI) standards for bacterial and endotoxin contamination 1, 3

Technical Considerations

Use dialyzers with biocompatible membranes for CRRT. 1, 3

Pre-dilution vs. Post-dilution:

• Consider pre-dilution fluid administration for patients with frequent filter clotting or when blood flow is limited 3

Equipment:

• Use integrated fluid balancing systems rather than adapted IV infusion pumps 3

Monitoring and Continuation

Continue CRRT as long as criteria defining severe AKI are present. 1

Discontinuation Criteria:

• Patient begins producing adequate urine output (typically after 10.6 ± 6.8 days) 4
• Renal function improves sufficiently to maintain internal homeostasis 4
• Absolute indications for RRT no longer present 1

Ongoing Monitoring:

• Assess filter performance continuously 3
• Monitor achievement of electrolyte, acid-base, solute, and fluid balance goals 1, 3
• Avoid volume overload, especially in patients with acute lung injury 3

Common Pitfalls to Avoid

• Do not delay RRT initiation until specific BUN/creatinine thresholds are reached; use comprehensive clinical assessment 4
• Do not use subclavian veins for access due to stenosis risk 2, 3
• Do not use lactate-buffered solutions in patients with shock, liver failure, or lactic acidosis 1, 3
• Do not assume prescribed dose equals delivered dose; frequent assessment is essential 1, 3