What are the different modalities of renal replacement therapy, including in‑center intermittent hemodialysis, home hemodialysis, peritoneal dialysis (CAPD and APD), continuous renal replacement therapies (CRRT) such as CVVH, CVVHD, CVVHDF, and kidney transplantation?

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Types of Renal Replacement Therapy

Renal replacement therapy encompasses several distinct modalities that can be categorized into extracorporeal treatments (hemodialysis-based) and intracorporeal treatment (peritoneal dialysis), with selection primarily driven by patient hemodynamic stability, clinical setting, and treatment goals. 1

Major RRT Modalities

Extracorporeal Kidney Replacement Therapy

Intermittent Hemodialysis (IHD)

  • Most commonly used modality for chronic kidney failure patients 1
  • Typically performed 3 times weekly for 3-4 hours per session 1
  • Suitable for hemodynamically stable patients with AKI/AKD or advanced CKD 1
  • Can be performed in-center or at home (home hemodialysis)
  • Uses diffusive clearance as primary mechanism

Intermittent Hemofiltration/Hemodiafiltration

  • Used in hypotension-prone chronic dialysis patients 1
  • Hemofiltration achieves clearance through convection
  • Most commonly, hemodialysis and hemofiltration are combined in the same session (hemodiafiltration) 1

Continuous Renal Replacement Therapy (CRRT)

  • Preferred for hemodynamically unstable patients and those with acute brain injury or increased intracranial pressure 1, 2
  • Duration: 8-24 hours daily (continuous) 1
  • Key advantages: better hemodynamic stability, slower solute shifts, better fluid removal tolerance 1
  • Specific CRRT modalities include:
    • CVVH (Continuous Venovenous Hemofiltration): predominantly convective clearance 3
    • CVVHD (Continuous Venovenous Hemodialysis): predominantly diffusive clearance 3
    • CVVHDF (Continuous Venovenous Hemodiafiltration): combines both dialysis and hemofiltration 3
    • CAVHDF (Continuous Arteriovenous Hemodiafiltration): less commonly used 4

Prolonged Intermittent Kidney Replacement Therapy (PIKRT)

  • Also called "hybrid therapies" or SLED (Sustained Low-Efficiency Dialysis) 1, 2
  • Combines characteristics of intermittent and continuous KRT 1
  • Reasonable alternative to CRRT in hemodynamically unstable adult patients 2
  • No clear advantage demonstrated for CRRT over PIKRT 1
  • May be associated with shortest hospital stay and mechanical ventilation days 4

Peritoneal Dialysis (PD)

Two main modalities:

  • CAPD (Continuous Ambulatory Peritoneal Dialysis): manual exchanges performed by patient at home, typically 4-5 times daily 1
  • APD (Automated Peritoneal Dialysis): exchanges performed by cycler machine, usually at home during nighttime 1

Clinical context:

  • Based on solute exchange between blood in peritoneal capillaries and dialysate introduced into peritoneal cavity 1
  • Uses hypertonic glucose or icodextrin solutions 1
  • Rarely used in adult ICU settings in Western countries 1
  • More frequent in hospitalized patients previously established on home PD 1
  • May be associated with shortest duration of renal support and ICU length of stay 4
  • Fewer complications (hypotension, bleeding) compared to extracorporeal modalities 4

Selection Algorithm Based on Clinical Context

For Chronic Kidney Failure (Stable Outpatients):

  • First-line: Intermittent hemodialysis (in-center or home) - most commonly used 1
  • Alternative: Peritoneal dialysis (CAPD or APD) for patient-centered care
  • Ultimate goal: Kidney transplantation

For Hemodynamically Stable AKI/AKD:

  • Intermittent hemodialysis is appropriate 1
  • PIKRT/SLED is reasonable alternative 2

For Hemodynamically Unstable AKI/AKD:

  • Preferred: CRRT or PIKRT 1, 2
  • Advantages: better hemodynamic stability, slower solute shifts, better fluid removal tolerance 1
  • No survival difference proven between CRRT and IHD, but CRRT better tolerated 4, 5

For Acute Brain Injury/Increased Intracranial Pressure:

  • Use CRRT rather than intermittent RRT 2
  • Rationale: slower solute flux per unit time reduces risk of cerebral edema from rapid osmotic shifts 2

For Patients with LVADs:

  • Peritoneal dialysis represents attractive alternative due to smaller hemodynamic shifts, no need for venous catheters, and better chance at renal recovery 6
  • Hemodialysis carries higher risk of hemodynamic disturbances due to high ultrafiltration rates 6

Important Caveats

Modality equivalence: Current evidence shows no clear mortality difference between CRRT and intermittent hemodialysis 4, 5, though CRRT may increase renal recovery compared to IHD 4. Recent data suggest CRRT as first modality might be associated with less favorable outcomes in less severely ill patients (SOFA 3-10) 5.

Resource considerations: Selection should account for local expertise, nursing availability, and equipment resources 2, 7. Not all dialysis centers can accommodate complex patients (e.g., those with LVADs) 6.

Dosing targets:

  • Intermittent/extended RRT: Kt/V ≥1.2 per treatment, 3 times weekly 7
  • CRRT: effluent volume 20-25 mL/kg/hour 7
  • Peritoneal dialysis: 0.3 Kt/V per session 7

Anticoagulation: Regional citrate anticoagulation recommended for CRRT when no contraindications exist 7, though FDA-approved citrate solutions are not universally available in the United States 2.

References

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