What is the recommended first-line treatment for patients with acute kidney injury or severe kidney impairment requiring renal support, specifically regarding Continuous Renal Replacement Therapy (CRRT)?

Continuous Renal Replacement Therapy (CRRT) for Acute Kidney Injury

Continuous venovenous hemodiafiltration (CVVHDF) is the recommended first-line CRRT modality for patients with acute kidney injury requiring renal support, particularly for hemodynamically unstable patients. 1

Indications for CRRT

• CRRT should be initiated immediately when life-threatening changes in fluid, electrolyte, and acid-base balance exist in patients with acute kidney injury (AKI) 2
• CRRT is specifically indicated for:
  • Hemodynamically unstable patients requiring vasopressor support 1, 3
  • Patients with acute brain injury or increased intracranial pressure 1, 3
  • Patients with severe fluid overload unresponsive to diuretics 2, 3
  • Patients on extracorporeal life support (ECLS) such as ECMO 1, 3

Absolute Indications for Emergent Dialysis

• Severe hyperkalemia or rapidly rising potassium levels with ECG changes 2
• Severe symptomatic dysnatremia resistant to medical management 2
• Severe metabolic acidosis with impaired compensation 2
• Pulmonary edema or severe fluid overload causing respiratory compromise 2
• Uremic complications (encephalopathy, pericarditis, bleeding) 2

CRRT Modality Selection

• CVVHDF or CVVH are preferred for hemodynamically unstable patients 1
• CVVHDF combines both diffusive and convective clearance, making it versatile for managing various solute and fluid imbalances 4
• Intermittent hemodialysis may be considered for rapid correction of severe hyperkalemia in hemodynamically stable patients 2

Technical Aspects of CRRT Implementation

Vascular Access

• Preferred access sites (in order of preference):
  • Right jugular vein 1, 3
  • Femoral vein (less optimal in patients with increased body mass) 1, 3
  • Left jugular vein 1, 3
  • Avoid subclavian vein due to risk of thrombosis and stenosis 1, 3

Dosing

• Deliver an effluent volume of 20-25 mL/kg/h for all CRRT modalities 1, 3, 5
• Use bicarbonate-based replacement fluids rather than lactate-based solutions, especially in patients with shock, liver failure, or lactic acidemia 1, 3

Anticoagulation

• Regional citrate anticoagulation is recommended for patients without contraindications 1, 3
• For patients with heparin-induced thrombocytopenia, use direct thrombin inhibitors or Factor Xa inhibitors 3

Monitoring and Assessment During CRRT

• Regular assessment of electrolytes, acid-base status, and fluid balance is essential 3
• For patients recovering from RRT-dependent AKI, kidney recovery is defined as sustained independence from RRT for a minimum of 14 days 6
• Laboratory and clinical evaluation after cessation of acute RRT should occur within 3 days (and no later than 7 days) after the last RRT session 6

Transitioning from CRRT to Intermittent Modalities

• Consider transitioning from CRRT to intermittent hemodialysis when:
  • Vasopressor support has been discontinued 3
  • Hemodynamic stability has been achieved 3
  • Intracranial hypertension has resolved 3
  • Fluid balance can be adequately controlled by intermittent hemodialysis 3

Special Considerations

• For patients discharged while still receiving RRT, frequent review of kidney function should occur with weekly assessment of pre-dialysis serum creatinine values and regular assessment of residual kidney function 6
• Avoid excessive fluid removal and hypotension to prevent re-injury to the kidney and enhance likelihood of renal recovery 6
• Alternative markers of GFR not sensitive to muscle mass (e.g., cystatin C) or direct quantification of GFR should be considered in selected cases during recovery 6

Common Pitfalls to Avoid

• Don't rely solely on BUN and creatinine thresholds for initiating CRRT; consider the broader clinical context 3
• Avoid using subclavian veins for access due to risk of thrombosis and stenosis 1, 3
• Don't use lactate-buffered solutions in patients with liver failure or lactic acidosis 1, 3
• Avoid excessive anticoagulation in patients with bleeding risk 7
• Ensure appropriate drug dosing adjustments for patients on CRRT, as clearance differs from both normal kidney function and intermittent hemodialysis 7, 8