Continuous Renal Replacement Therapy (CRRT)

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, as defined by the Kidney International 1, 2
• CRRT is primarily used in critically ill patients with acute kidney injury (AKI) who are hemodynamically unstable, according to Critical Care Medicine 3
• CRRT represents approximately one-fourth of all renal replacement therapies used for acute renal failure in the United States, as reported by Kidney International 2

Main Modalities of CRRT

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

Indications for CRRT

• Hemodynamically unstable patients with AKI who cannot tolerate intermittent hemodialysis are indicated for CRRT, according to Critical Care Medicine and American Journal of Kidney Diseases 3, 4
• Patients with or at risk for cerebral edema are indicated for CRRT, according to Kidney International and American Journal of Kidney Diseases 5, 4
• Patients requiring continuous fluid removal or management of volume overload are indicated for CRRT, according to Critical Care Medicine and American Journal of Kidney Diseases 3, 6
• Patients with severe acid-base disturbances requiring continuous correction are indicated for CRRT, according to Praxis Medical Insights 6
• Patients with septic shock, acute respiratory distress syndrome (ARDS), or burns who may benefit from continuous removal of inflammatory mediators are indicated for CRRT, according to Kidney International 5

Technical Aspects and Prescription

Access and Setup

• Uncuffed nontunneled dialysis catheters are recommended for initiating CRRT in AKI patients, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• The preferred vein selection order is right jugular vein, femoral vein, left jugular vein, and subclavian vein, as recommended by American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• Ultrasound guidance should always be used for catheter insertion, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• Chest radiograph is required after placement and before first use of internal jugular or subclavian catheters, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• Biocompatible membrane dialyzers should be used for CRRT, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6

Anticoagulation

• Patient's bleeding risk must be assessed before selecting an anticoagulation strategy, according to Praxis Medical Insights 6
• Regional citrate anticoagulation is the first choice for patients without increased bleeding risk, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• Unfractionated or low-molecular-weight heparin can be used if citrate is contraindicated, according to Praxis Medical Insights 6
• For patients with heparin-induced thrombocytopenia (HIT), direct thrombin inhibitors or Factor Xa inhibitors should be used, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6

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, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• All dialysis and replacement fluids must comply with American Association of Medical Instrumentation (AAMI) standards for bacterial and endotoxin contamination, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• Pre-dilution fluid administration may be beneficial for patients with frequent filter clotting or when extracorporeal clearance is limited by achievable blood flow, according to Kidney International and Praxis Medical Insights 1, 6

Dosing and Monitoring

• The recommended effluent volume for CRRT in AKI is 20-25 mL/kg/h, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• The actual delivered dose should be frequently assessed and prescription adjusted accordingly, according to American Journal of Kidney Diseases and Praxis Medical Insights 4, 6
• Monitoring should focus on filter performance and achieving goals of electrolyte balance, acid-base balance, solute clearance, and fluid balance, according to Praxis Medical Insights 6
• Volume overload should be avoided, especially in patients with acute lung injury, according to Kidney International and Praxis Medical Insights 1, 6

Advantages of CRRT Over Intermittent Hemodialysis

• Greater hemodynamic stability in critically ill patients, according to Critical Care Medicine 3
• Better management of fluid balance, according to Critical Care Medicine 3
• More effective for patients with cerebral edema or increased intracranial pressure, according to Kidney International and American Journal of Kidney Diseases 5, 4

Common Pitfalls and Considerations

• Avoid using subclavian veins for access due to risk of thrombosis and late stenosis, according to Praxis Medical Insights 6
• Don't rely solely on BUN and creatinine thresholds for initiating RRT; consider broader clinical context, according to Praxis Medical Insights 6
• Avoid using lactate-buffered solutions in patients with liver failure or lactic acidosis, according to Kidney International and Praxis Medical Insights 1, 6
• Integrated fluid balancing systems should be used rather than adapted intravenous infusion pumps, according to Kidney International and Praxis Medical Insights 1, 6

Immediate Initiation of Continuous Renal Replacement Therapy (CRRT)

Absolute Indications for RRT

• Severe respiratory compromise with markedly low oxygen saturation despite 100 % inspired oxygen is considered an absolute indication for starting renal replacement therapy in critically ill patients. 7

Preference for CRRT Over Intermittent Hemodialysis

• In patients who require vasopressor support for hemodynamic instability, intermittent hemodialysis is poorly tolerated and CRRT is the recommended modality. 8
• CRRT’s continuous, gentle fluid removal is advantageous in severe acute respiratory distress syndrome because it avoids rapid intravascular volume shifts that can aggravate pulmonary edema. 7

Protocol‑Based Guidance on Diuretic Use

• The FACTT‑lite protocol advises that aggressive diuresis should be employed only when the patient is hemodynamically stable and off vasopressors for at least 12 hours; therefore, escalating loop diuretics in a vasopressor‑dependent shock state is contraindicated. 7

Therapeutic Goals of CRRT

• Aim for a net negative fluid balance of 1–2 L during the first 24 hours of CRRT to enhance oxygenation while continuously monitoring hemodynamics. 7

Monitoring Expected Outcomes

• During CRRT, clinicians should anticipate improvement in oxygenation parameters (reduced FiO₂ requirements and higher arterial oxygen saturation) as volume overload is corrected. 7