What are the guidelines for initiating Continuous Renal Replacement Therapy (CRRT) in patients with severe acute kidney injury or renal impairment?

Guidelines for Initiating CRRT in Patients with Acute Kidney Injury

Initiate CRRT emergently when life-threatening changes in fluid, electrolyte, and acid-base balance exist, and preferentially use CRRT over intermittent hemodialysis in hemodynamically unstable patients requiring vasopressor support. 1, 2

Absolute Indications for Emergent CRRT Initiation

Life-threatening complications require immediate CRRT initiation regardless of laboratory values: 1, 2

• Severe hyperkalemia with ECG changes (peaked T waves, widened QRS, or arrhythmias) 2
• Pulmonary edema or severe fluid overload causing respiratory compromise unresponsive to diuretics 2
• Severe metabolic acidosis with impaired respiratory compensation 2
• Uremic complications including encephalopathy, pericarditis, or bleeding diathesis 2
• Severe symptomatic dysnatremia resistant to medical management 2

Preferred Clinical Scenarios for CRRT Over Intermittent Hemodialysis

CRRT is the preferred modality in the following situations: 1, 2

• Hemodynamically unstable patients requiring vasopressor support - CRRT provides better hemodynamic stability with slower solute shifts 1
• Acute brain injury with increased intracranial pressure or generalized cerebral edema - slower solute flux prevents rapid osmotic shifts that can worsen cerebral edema 1, 2
• Patients on extracorporeal life support (ECMO) 2
• Severe fluid overload requiring precise fluid balance control 2, 3

Non-Emergent Initiation: The "Broader Clinical Context" Approach

When life-threatening complications are absent, initiate CRRT based on clinical trajectory rather than single laboratory thresholds: 1

Key Clinical Factors to Consider:

• Trends in kidney function - rising creatinine and BUN over time, not absolute values 1
• Volume status assessment - progressive fluid accumulation despite diuretic therapy 1
• Response to diuretic administration - oliguria or anuria despite adequate diuretic dosing 1
• Presence of conditions modifiable by RRT - uremic symptoms, refractory metabolic acidosis, or electrolyte abnormalities 1
• Patient's overall clinical trajectory - worsening multi-organ dysfunction 1

Important caveat: The guidelines acknowledge substantial variability in practice and limited evidence for optimal timing in non-emergent situations. 1 In Canadian practice, hyperkalemia and volume expansion factor most strongly in decision-making, while absolute creatinine and urea values influence only 57-59% of clinicians. 1

Technical Specifications for CRRT Delivery

Dosing Parameters:

• Deliver an effluent volume of 20-25 mL/kg/h for all CRRT modalities 1, 2
• Prescribe higher effluent volumes to account for downtime from procedures or circuit clotting 1
• Use CVVHDF or CVVH modalities for hemodynamically unstable patients 2

Fluid Composition:

• Use bicarbonate-based replacement fluids rather than lactate-based solutions, especially in patients with shock, liver failure, or lactic acidemia 2, 3, 4

Anticoagulation Strategy

Regional citrate anticoagulation is preferred over heparin in patients without contraindications: 1, 5

Anticoagulation Algorithm:

1. First-line: Regional citrate anticoagulation for patients without severe liver dysfunction 1, 5
2. Contraindications to citrate: severe liver failure with impaired citrate metabolism 5
3. If citrate contraindicated: use unfractionated or low-molecular-weight heparin 1
4. Patients with increased bleeding risk: prefer citrate over heparin, or run without anticoagulation if citrate contraindicated 1, 5
5. Heparin-induced thrombocytopenia (HIT): stop all heparin immediately and use direct thrombin inhibitors (argatroban) or Factor Xa inhibitors (danaparoid, fondaparinux) 1, 5

Critical monitoring for citrate anticoagulation: 5

• Systemic ionized calcium levels
• Acid-base balance
• Serum sodium (risk of hypernatremia)
• Total calcium/ionized calcium ratio to detect citrate accumulation

Common Pitfalls to Avoid

Do not rely solely on single BUN or creatinine thresholds - this approach lacks evidence and ignores clinical context 1

Avoid excessive fluid removal and hypotension - this can cause re-injury to recovering kidneys and reduce likelihood of renal recovery 2

Do not use FDA-unapproved citrate solutions for regional anticoagulation in the United States, as no FDA-approved citrate solutions currently exist for this indication 1

Monitor for CRRT-induced electrolyte disturbances: 3, 4

• Hypophosphatemia
• Hypokalemia
• Hypomagnesemia (especially with citrate anticoagulation due to magnesium-citrate complex losses)

Transitioning and Discontinuation

Consider transitioning from CRRT to intermittent hemodialysis when: 2

• Vasopressor support has been discontinued
• Hemodynamic stability achieved
• Intracranial hypertension resolved (if applicable)
• Fluid balance can be adequately controlled by intermittent modalities

Discontinue CRRT when: 1

• Intrinsic kidney function has recovered sufficiently to meet patient needs
• RRT is no longer consistent with goals of care

Define kidney recovery as: sustained independence from RRT for minimum of 14 days 2