Why is Continuous Renal Replacement Therapy (CRRT) preferred over Intermittent Hemodialysis (iHD) in patients with severe renal failure?

Indications for Continuous Renal Replacement Therapy (CRRT) over Intermittent Hemodialysis (IHD)

CRRT is recommended over intermittent hemodialysis for patients with acute kidney injury who have hemodynamic instability or who are at risk for cerebral edema. 1, 2

Key Indications for CRRT

Hemodynamic Instability

• CRRT is preferred for hemodynamically unstable patients with acute kidney injury (AKI) due to its ability to provide gradual fluid removal without significant blood pressure fluctuations 1
• The continuous nature of CRRT allows for better maintenance of cardiovascular stability compared to the rapid fluid shifts associated with intermittent hemodialysis 2
• CRRT facilitates management of fluid balance in patients who cannot tolerate the rapid fluid removal of intermittent treatments 1

Cerebral Edema and Increased Intracranial Pressure

• CRRT is strongly recommended over IHD for patients with AKI who have, or are at risk for, cerebral edema 1
• The gradual solute removal with CRRT prevents rapid osmotic shifts that could worsen cerebral edema 2
• This recommendation carries a grade C evidence level according to international consensus guidelines 1

Fluid Management in Critical Illness

• CRRT provides superior control of fluid balance in patients requiring careful volume management 1, 2
• Patients with conditions such as septic shock, acute respiratory distress syndrome (ARDS), or burns benefit from the continuous removal of volume and inflammatory mediators 1, 3
• CRRT allows for unlimited nutritional support without concerns about fluid overload between dialysis sessions 4

Technical Advantages of CRRT

Solute Control

• CRRT provides continuous clearance of uremic toxins without the peaks and valleys seen in intermittent therapies 2
• The recommended effluent volume for CRRT in AKI is 20-25 mL/kg/h to ensure adequate solute clearance 1
• Continuous therapy allows for better control of acid-base balance and electrolyte abnormalities 2

Modalities of CRRT

• Various CRRT modalities are available to tailor treatment to patient needs:
  • Continuous Venovenous Hemofiltration (CVVH) - primarily convective clearance
  • Continuous Venovenous Hemodialysis (CVVHD) - primarily diffusive clearance
  • Continuous Venovenous Hemodiafiltration (CVVHDF) - combines both clearance methods 2

Limitations and Considerations

Lack of Mortality Benefit

• Despite theoretical advantages, multiple studies and meta-analyses have not demonstrated a clear survival advantage of CRRT over IHD 1, 5
• The 2013 Surviving Sepsis Campaign guidelines state that continuous and intermittent therapies achieve similar short-term survival rates 1
• Some recent research even suggests potential concerns with CRRT in less severely ill patients 6

Practical Considerations

• CRRT requires continuous anticoagulation, which may increase bleeding risk 4
• Patient immobilization is necessary during CRRT 4
• CRRT is generally more resource-intensive and costly than intermittent hemodialysis 3, 5

Clinical Decision Algorithm

1. Assess hemodynamic stability:

   • If patient has hypotension, vasopressor requirements, or cardiovascular instability → Choose CRRT 1
   • If patient is hemodynamically stable → IHD may be appropriate 4

2. Evaluate neurological status:

   • If patient has cerebral edema, traumatic brain injury, or increased intracranial pressure → Choose CRRT 1
   • If neurological status is normal → Either modality is acceptable

3. Consider fluid management needs:

   • If precise fluid control is critical (e.g., ARDS, severe heart failure) → Choose CRRT 2, 3
   • If fluid management is less challenging → Either modality is acceptable

4. Assess resource availability:

   • Consider local expertise, staffing, and equipment availability 5
   • In resource-limited settings, IHD may be more practical 7

Common Pitfalls to Avoid

• Don't rely solely on BUN and creatinine thresholds for initiating RRT; consider the broader clinical context 2
• Avoid using lactate-buffered solutions in CRRT for patients with liver failure or lactic acidosis 1, 2
• Don't use subclavian veins for vascular access due to risk of thrombosis and stenosis 2
• Remember that CRRT is not superior to IHD for treatment of acute intoxications or severe hyperkalemia due to its slower clearance 4