What is Continuous Renal Replacement Therapy (CRRT)?

Continuous Renal Replacement Therapy (CRRT)

CRRT is defined as any extracorporeal blood purification therapy intended to substitute for impaired renal function over an extended period of time and applied for, or aimed at being applied for, 24 hours per day. 1

Definition and Basic Principles

• CRRT is a form of renal replacement therapy that provides continuous, gradual purification of blood over extended periods (24 hours/day) rather than intermittent treatments 1
• CRRT is primarily used in critically ill patients with acute kidney injury (AKI) who are hemodynamically unstable 1, 2
• CRRT allows for gentle, continuous removal of fluids, electrolytes, and solutes without causing significant hemodynamic changes 2
• CRRT represents approximately one-fourth of all renal replacement therapies used for acute renal failure in the United States 1

Main Modalities of CRRT

Different CRRT techniques exist based on the mechanism of solute clearance:

• Continuous Venovenous Hemofiltration (CVVH): Uses primarily convective clearance through a highly permeable membrane 1, 2
• Continuous Venovenous Hemodialysis (CVVHD): Uses primarily diffusive clearance across a semipermeable membrane 1, 2
• Continuous Venovenous Hemodiafiltration (CVVHDF): Combines both convective and diffusive clearance methods 1, 2
• Continuous Venovenous High-Flux Dialysis (CVVHFD): Uses a highly permeable dialyzer with countercurrent blood and dialysate flow, balancing filtration and back-filtration 1
• Continuous High-Volume Hemofiltration: A variant of CVVH using higher surface area filters and ultrafiltration volumes greater than 35 mL/hour/kg 1

Indications for CRRT

CRRT is particularly indicated for:

• Hemodynamically unstable patients with AKI who cannot tolerate intermittent hemodialysis 1
• Patients with or at risk for cerebral edema 1
• Patients requiring continuous fluid removal or management of volume overload 1, 3
• Patients with severe acid-base disturbances requiring continuous correction 3, 2
• Patients with septic shock, acute respiratory distress syndrome (ARDS), or burns who may benefit from continuous removal of inflammatory mediators 1

Technical Aspects and Prescription

Access and Setup

• Uncuffed nontunneled dialysis catheters are recommended for initiating CRRT in AKI patients 1, 3
• Preferred vein selection order: right jugular vein (first choice), femoral vein (second), left jugular vein (third), and subclavian vein (last choice) 1, 3
• Ultrasound guidance should always be used for catheter insertion 1, 3
• Chest radiograph is required after placement and before first use of internal jugular or subclavian catheters 1, 3
• Biocompatible membrane dialyzers should be used for CRRT 1, 3

Anticoagulation

• Patient's bleeding risk must be assessed before selecting an anticoagulation strategy 3
• Regional citrate anticoagulation is the first choice for patients without increased bleeding risk 1, 3
• Unfractionated or low-molecular-weight heparin can be used if citrate is contraindicated 3
• For patients with heparin-induced thrombocytopenia (HIT), direct thrombin inhibitors or Factor Xa inhibitors should be used 1, 3

Fluid Composition

• Bicarbonate is preferred over lactate as buffer in dialysate and replacement fluid, especially for patients with circulatory shock, liver failure, or lactic acidemia 1, 3
• All dialysis and replacement fluids must comply with American Association of Medical Instrumentation (AAMI) standards for bacterial and endotoxin contamination 1, 3
• Pre-dilution fluid administration may be beneficial for patients with frequent filter clotting or when extracorporeal clearance is limited by achievable blood flow 1, 3

Dosing and Monitoring

• The recommended effluent volume for CRRT in AKI is 20-25 mL/kg/h 1, 3, 4
• The actual delivered dose should be frequently assessed and prescription adjusted accordingly 1, 3
• Monitoring should focus on filter performance and achieving goals of electrolyte balance, acid-base balance, solute clearance, and fluid balance 3, 4
• Volume overload should be avoided, especially in patients with acute lung injury 1, 3

Advantages of CRRT Over Intermittent Hemodialysis

• Greater hemodynamic stability in critically ill patients 1, 2
• Better management of fluid balance 1, 2
• More continuous and physiologic approach to renal support 5, 2
• More effective for patients with cerebral edema or increased intracranial pressure 1
• Better control of acid-base and electrolyte disturbances 2

Common Pitfalls and Considerations

• Avoid using subclavian veins for access due to risk of thrombosis and late stenosis 3
• Don't rely solely on BUN and creatinine thresholds for initiating RRT; consider broader clinical context 3
• Avoid using lactate-buffered solutions in patients with liver failure or lactic acidosis 1, 3
• Antibiotic dosing may need adjustment during CRRT due to altered drug clearance 5, 6
• Integrated fluid balancing systems should be used rather than adapted intravenous infusion pumps 1, 3

Special Populations

• In pediatric patients, CRRT is also the preferred method for renal support in critically ill and hemodynamically unstable children 7
• Timely transfer to centers with CRRT expertise is recommended for pediatric patients with worsening AKI or fluid overload 7