Does Continuous Renal Replacement Therapy (CRRT) include Peritoneal Dialysis (PD) or just Continuous Veno-Venous Hemofiltration (CVVH), Continuous Veno-Venous Hemodialysis (CVVHD), and Continuous Veno-Venous Hemodiafiltration (CVVHDF)?

Continuous Renal Replacement Therapy (CRRT) Does Not Include Peritoneal Dialysis

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, which includes CVVH, CVVHD, and CVVHDF, but does not include peritoneal dialysis. 1

Definition and Modalities of CRRT

• CRRT specifically refers to extracorporeal blood purification therapies that are applied continuously (24 hours per day) to substitute for impaired renal function 1
• The basic modes of CRRT include:
  • CVVH (Continuous Venovenous Hemofiltration): Uses convection as the primary mechanism of solute removal, where ultrafiltrate is produced and replaced with replacement solution 2
  • CVVHD (Continuous Venovenous Hemodialysis): Uses diffusion as the primary mechanism, where dialysate flows countercurrent to blood flow across a semipermeable membrane 2
  • CVVHDF (Continuous Venovenous Hemodiafiltration): Combines both diffusive and convective solute removal 1
• Other recognized CRRT variants include:
  • CVVHFD (Continuous Venovenous High-Flux Dialysis): Uses a highly permeable dialyzer with countercurrent blood and dialysate flow 1
  • Continuous High-Volume Hemofiltration: A variant of CVVH using higher surface area hemofilters and ultrafiltration volumes >35 mL/hour/kg 1

Why Peritoneal Dialysis Is Not CRRT

• CRRT by definition requires an extracorporeal circuit for blood purification, whereas PD uses the patient's peritoneum as the dialysis membrane 1
• In guidelines discussing both modalities, PD is clearly distinguished from CRRT as a separate treatment option 1
• When CRRT is unavailable, PD is mentioned as an alternative therapy, further confirming they are distinct modalities 1

Clinical Distinctions Between CRRT and PD

• CRRT requires vascular access (typically venovenous) and uses an external filter/dialyzer for blood purification 3
• PD uses the peritoneal membrane as the dialysis surface and requires insertion of a peritoneal catheter rather than vascular access 1
• In clinical practice, CRRT is preferred over PD for critically ill patients due to:
  • More predictable solute clearance 1
  • Better control of fluid balance 3
  • More rapid correction of severe metabolic derangements 1

Evidence from Clinical Guidelines

• The First International Consensus Conference on CRRT explicitly defines CRRT as extracorporeal blood purification therapy, which excludes PD by definition 1
• Clinical guidelines clearly separate recommendations for PD from those for CRRT, treating them as distinct modalities 1
• When discussing treatment options for conditions like hyperammonemia, guidelines present PD as an alternative to CRRT when the latter is unavailable, confirming they are different modalities 1

Technical Considerations

• CRRT modalities (CVVH, CVVHD, CVVHDF) all use blood pumps and extracorporeal circuits 1
• Venovenous therapies are preferred to arteriovenous therapies due to higher solute clearance rates and reduced risk of complications 1
• CRRT requires specialized equipment including blood pumps, filters, and integrated fluid balancing systems 3
• PD relies on diffusion and osmosis across the peritoneal membrane rather than an extracorporeal circuit 1

In clinical practice, the distinction between CRRT and PD is important for treatment selection, as each has different indications, contraindications, and resource requirements. While both can be used for renal replacement in acute kidney injury, they represent fundamentally different approaches to therapy 1, 3.