What is the recommended treatment approach for patients requiring renal replacement therapy due to acute kidney injury or severe kidney impairment, specifically regarding Continuous Renal Replacement Therapy (CRRT)?

Continuous Renal Replacement Therapy (CRRT) for Acute Kidney Injury

CRRT is the recommended first-line renal replacement therapy for hemodynamically unstable patients with acute kidney injury and for patients with acute brain injury or increased intracranial pressure. 1

Indications for CRRT

• CRRT is preferred over intermittent hemodialysis for hemodynamically unstable patients due to better cardiovascular tolerance and more gradual solute clearance 1, 2
• CRRT is recommended for AKI patients with acute brain injury, increased intracranial pressure, or generalized brain edema 1, 2
• CRRT should be used for patients requiring continuous management of fluid overload, electrolyte abnormalities, or acid-base disturbances 2
• CRRT represents approximately 25% of all renal replacement therapies for acute renal failure in the United States 2

CRRT Modalities

• Continuous Venovenous Hemofiltration (CVVH): Uses primarily convective clearance through a highly permeable membrane 2
• Continuous Venovenous Hemodialysis (CVVHD): Uses primarily diffusive clearance across a semipermeable membrane 2
• Continuous Venovenous Hemodiafiltration (CVVHDF): Combines both convective and diffusive clearance methods 2
• Prolonged Intermittent Renal Replacement Therapy (PIRRT/SLED): Can be considered as an alternative to CRRT in hemodynamically unstable adult patients where CRRT is not available 1

Technical Aspects of CRRT

Vascular Access

• Use uncuffed non-tunneled dialysis catheters to initiate CRRT in AKI patients 1, 2
• Preferred vein selection order: right jugular vein (first), femoral vein (second), left jugular vein (third), and subclavian vein (last) 1, 2
• Always use ultrasound guidance for catheter insertion to minimize complications 1, 2
• Obtain chest radiograph after placement and before first use of internal jugular or subclavian catheters 1, 2

Anticoagulation

• For patients without increased bleeding risk:
  • Regional citrate anticoagulation is preferred for CRRT when there are no contraindications 1, 2
  • If citrate is contraindicated, use unfractionated or low-molecular-weight heparin 1, 2
• For patients with increased bleeding risk:
  • Consider regional citrate anticoagulation if no contraindications exist 1
  • Avoid regional heparinization 1
• For patients with heparin-induced thrombocytopenia (HIT):
  • Use direct thrombin inhibitors (argatroban) or Factor Xa inhibitors 1
  • Argatroban is preferred in patients without severe liver failure 1

Dialysate and Replacement Fluid

• Use bicarbonate rather than lactate as buffer in dialysate and replacement fluid 1, 2
• Bicarbonate is strongly recommended (1B) for patients with AKI and circulatory shock 1
• Bicarbonate is suggested (2B) for patients with AKI and liver failure and/or lactic acidemia 1
• All fluids must comply with AAMI standards for bacterial and endotoxin contamination 1
• Use biocompatible membrane dialyzers 1, 2

CRRT Dosing and Monitoring

• Deliver an effluent volume of 20-25 mL/kg/h for CRRT in AKI 1, 2
• This typically requires a higher prescription of effluent volume to account for treatment interruptions 1
• Prescribe the dose before starting each session and frequently assess the actual delivered dose 1
• Monitor filter performance, electrolyte balance, acid-base status, solute clearance, and fluid balance 2
• Avoid volume overload, especially in patients with acute lung injury 2

Common Pitfalls and Considerations

• Avoid subclavian vein access when possible due to risk of stenosis with large catheters 1
• Don't rely solely on BUN and creatinine thresholds for initiating RRT; consider the broader clinical context 2
• Avoid lactate-buffered solutions in patients with liver failure or lactic acidosis 1, 2
• Be cautious with regional citrate anticoagulation in patients with severe liver failure due to risk of citrate accumulation 1
• Monitor the total calcium to ionized calcium ratio when using citrate anticoagulation in patients with liver dysfunction 1
• Recent evidence suggests that in less severely ill patients (SOFA score 3-10), intermittent hemodialysis may be associated with better survival than CRRT 3

Discontinuation of CRRT

• CRRT should be discontinued when kidney function has recovered or when RRT becomes inconsistent with care goals 1
• Consider transitioning from CRRT to intermittent hemodialysis when vasopressor support has been stopped, intracranial hypertension has resolved, and fluid balance can be controlled with intermittent therapy 1

CRRT remains an essential modality for supporting critically ill patients with AKI, particularly those with hemodynamic instability or increased intracranial pressure, though the optimal timing of initiation remains uncertain and requires additional research 1.