What are the typical settings for Continuous Renal Replacement Therapy (CRRT)?

Typical CRRT Settings

The typical CRRT effluent dose should be delivered at 20-25 mL/kg/h for patients with acute kidney injury, with a prescription of 25-30 mL/kg/h to account for treatment interruptions and filter efficiency decline over time. 1, 2

CRRT Modalities

• 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 24 hours per day 1
• Common CRRT modalities include: 1
  • CVVH (Continuous Venovenous Hemofiltration): Uses convection as primary mechanism with an external pump in a venovenous circuit
  • CVVHD (Continuous Venovenous Hemodialysis): Uses diffusion with an external pump in a venovenous circuit
  • CVVHDF (Continuous Venovenous Hemodiafiltration): Combines both diffusive and convective solute removal
  • SCUF (Slow Continuous Ultrafiltration): Form of CVVH without fluid replacement, primarily for fluid removal

Vascular Access

• Recommended order of preference for catheter insertion: right internal jugular vein, femoral vein, left internal jugular vein, with subclavian vein as last choice 3
• Always use ultrasound guidance for dialysis catheter insertion 3
• Obtain chest radiograph promptly after placement of internal jugular or subclavian catheters 3
• Avoid subclavian veins for access due to risk of thrombosis and late stenosis 3, 1

Anticoagulation Protocol

• Assess patient's bleeding risk before selecting anticoagulation strategy 3
• For patients without increased bleeding risk:
  • Regional citrate anticoagulation is recommended as first choice 3
  • Unfractionated or low-molecular-weight heparin if citrate is contraindicated 3
• For patients with increased bleeding risk:
  • Consider regional citrate anticoagulation if no contraindications exist 3
  • CRRT can be carried out without anticoagulation in patients who are auto-anticoagulated or at high risk of bleeding 1
• For patients with heparin-induced thrombocytopenia:
  • Use direct thrombin inhibitors or Factor Xa inhibitors 3

Fluid Composition

• Use bicarbonate rather than lactate as buffer in dialysate and replacement fluid 3, 1
• Bicarbonate is especially important for patients with circulatory shock, liver failure, and/or lactic acidemia 3
• Dialysate or substitution fluid should contain physiologic concentrations of electrolytes 1
• Avoid fluids with supra-physiologic glucose concentrations to prevent hyperglycemia 1, 3
• Consider pre-dilution fluid administration for patients with frequent filter clotting or when extracorporeal clearance is limited by achievable blood flow 1, 3

Dosing Parameters

• Prescribed effluent dose: 25-30 mL/kg/h to account for treatment interruptions and filter efficiency decline 1, 2
• Delivered effluent dose: Target 20-25 mL/kg/h 1, 2
• For CVVHD: Typical dialysate flow rates are 1-2 L/hour 1
• For high-volume hemofiltration: Ultrafiltration volumes greater than 35 mL/hour/kg 1
• Blood flow rate: Typically 100-150 mL/min for CVVHDF 1

Monitoring and Adjustments

• Frequently assess actual delivered dose to adjust prescription as needed 3
• Monitor filter performance and adjust prescription to achieve goals of electrolyte balance, acid-base balance, solute clearance, and fluid balance 3
• During heparin anticoagulation, measure activated clotting times (ACT) or systemic partial thromboplastin time (PTT) 1
• During citrate anticoagulation, frequently measure post-filter and serum-ionized calcium to titrate citrate and calcium replacement solutions 1
• Monitor for filter performance and adjust prescription as needed 3

Equipment Considerations

• Use integrated fluid balancing systems rather than intravenous infusion pumps adapted for CRRT 3
• Adaptive use of intravenous infusion pumps for CRRT has been shown to risk significant errors in fluid balance 1
• Use dialyzers with a biocompatible membrane 3

Common Pitfalls to Avoid

• Not accounting for treatment interruptions when prescribing dose 2
• Using lactate-buffered solutions in patients with liver failure or lactic acidosis 1, 3
• Relying on subclavian veins for access due to risk of thrombosis and late stenosis 1, 3
• Not monitoring the actual delivered dose, which often falls short of the prescribed dose 1
• Using diuretics to enhance kidney function recovery or reduce duration/frequency of RRT 3

By following these evidence-based settings and monitoring protocols, CRRT can be effectively delivered to optimize outcomes in critically ill patients with acute kidney injury.