What are the CRRT (continuous renal replacement therapy) considerations—including indications, initiation thresholds, vascular access, modality selection, anticoagulation strategy, effluent dose, monitoring, hemodynamic management, and discontinuation criteria—in hemodynamically unstable critically ill patients with acute kidney injury and severe fluid overload or refractory electrolyte/acid‑base disturbances?

CRRT Considerations in Hemodynamically Unstable Critically Ill Patients

Indications for CRRT Initiation

CRRT should be initiated immediately for hemodynamically unstable patients with acute kidney injury when life-threatening metabolic derangements exist, and is specifically preferred over intermittent hemodialysis in patients requiring vasopressor support, those with acute brain injury or increased intracranial pressure, and those with severe fluid overload unresponsive to diuretics. 1, 2, 3

Absolute Emergent Indications

• Severe hyperkalemia with ECG changes 2
• Diuretic-unresponsive pulmonary edema causing respiratory compromise 1, 2
• Severe metabolic acidosis with impaired compensation 2
• Uremic complications (encephalopathy, pericarditis, bleeding) 1, 2
• Severe symptomatic dysnatremia resistant to medical management 2

Specific Clinical Scenarios Favoring CRRT

• Hemodynamic instability requiring vasopressor support 1, 2, 3
• Acute brain injury or risk for cerebral edema (CRRT strongly recommended over intermittent hemodialysis due to lower risk of intracranial pressure fluctuations) 1, 4
• Patients on extracorporeal life support (ECMO, ventricular assist devices) 1, 2, 3, 4
• Septic shock, ARDS, or burns requiring continuous volume removal 1

Critical Pitfall: Do not wait for conventional chronic kidney disease thresholds (specific BUN or creatinine values) to initiate therapy in critically ill patients, as consequences of metabolic complications are more severe in this population; begin therapy before complications develop. 1, 4

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Vascular Access Strategy

The right internal jugular vein is the first-choice access site, followed by femoral vein (though inferior in obese patients), then left internal jugular vein, with subclavian vein avoided due to thrombosis and stenosis risk. 1, 2, 3, 4

Access Site Selection Algorithm

1. First choice: Right internal jugular vein 2, 3, 4
2. Second choice: Femoral vein (avoid in patients with high BMI) 2, 3, 4
3. Third choice: Left internal jugular vein 2, 3, 4
4. Last resort: Subclavian vein (avoid when possible due to thrombosis/stenosis risk) 1, 2, 3, 4

Catheter Selection and Insertion

• Use uncuffed non-tunneled dialysis catheter of appropriate length and gauge for acute initiation 1, 4
• Consider cuffed catheter if prolonged RRT expected 1
• Always use ultrasound guidance for insertion 4
• Obtain chest radiograph before first use of internal jugular or subclavian catheters 4

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Modality Selection

CVVHDF (continuous venovenous hemodiafiltration) or CVVH (continuous venovenous hemofiltration) are the preferred modalities for hemodynamically unstable patients. 2, 3

Modality-Specific Recommendations

• CVVHDF or CVVH: Preferred for hemodynamic instability, acute brain injury, severe fluid overload, and patients on ECLS 2, 3, 4
• Intermittent hemodialysis: May be considered only for rapid correction of severe hyperkalemia in hemodynamically stable patients 2

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Anticoagulation Strategy

Regional citrate anticoagulation is recommended as first-line for patients without contraindications, as it provides superior filter life and reduced bleeding risk compared to systemic heparinization. 1, 2, 3, 4

Anticoagulation Algorithm

• First-line: Regional citrate anticoagulation (if no contraindications) 1, 2, 3, 4
• Heparin-induced thrombocytopenia: Use direct thrombin inhibitors (argatroban) or Factor Xa inhibitors 4
• Increased bleeding risk: Avoid regional heparinization; consider no anticoagulation or citrate 4

Citrate-Specific Monitoring

• Monitor ionized calcium and total calcium/ionized calcium ratio to detect citrate accumulation 2
• Citrate metabolism generates bicarbonate, which can affect acid-base interpretation 2

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Effluent Dose Prescription

Deliver an effluent volume of 20-25 mL/kg/h for all CRRT modalities, recognizing that prescribed dose must be higher than delivered dose to achieve target. 1, 2, 3, 4

Dosing Considerations

• Target delivered dose: 20-25 mL/kg/h 1, 2, 3, 4
• Prescribe higher than target to account for downtime and interruptions 1
• Systematically monitor prescribed versus delivered dose 5

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Fluid Composition and Buffer Selection

Bicarbonate-based replacement fluids are strongly preferred over lactate-based solutions, especially in hemodynamically unstable patients with shock, liver failure, or lactic acidemia. 1, 2, 3, 4

Buffer Selection Algorithm

• Bicarbonate: Preferred for shock states, liver failure, lactic acidosis, and high-volume hemofiltration 1, 2, 3, 4
• Lactate: Acceptable only in stable patients without liver dysfunction or lactic acidosis 1
• Avoid lactate in: Lactic acidosis, liver failure, or hemodynamic instability (worsening acidosis documented) 1, 4

Fluid Management Principles

• Use physiologic electrolyte concentrations except in extreme imbalances 1
• Avoid supra-physiologic glucose concentrations (causes hyperglycemia) 1
• Pre-dilution may enhance ultrafiltration rates and reduce filter clotting 1

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Hemodynamic Management During CRRT

CRRT provides superior hemodynamic tolerance compared to intermittent modalities, but avoid excessive fluid removal and hypotension to prevent kidney re-injury and enhance recovery potential. 2, 4, 6

Volume Management Strategy

• Maintain negative fluid balance to decrease ICU length of stay, especially in acute lung injury 1
• Avoid volume overload (associated with adverse outcomes) 1
• Prevent excessive fluid removal that causes hypotension (impairs renal recovery) 2
• Use integrated fluid balancing systems designed for CRRT (avoid adapted IV pumps due to error risk) 1

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Monitoring Requirements

Regular assessment of electrolytes, acid-base status, fluid balance, and filter performance is essential, with particular attention to preventing CRRT-induced electrolyte disturbances such as hypokalemia and hypophosphatemia. 2, 6, 7

Monitoring Protocol

• Electrolytes and acid-base status: Frequent assessment 2, 7
• Fluid balance: Continuous monitoring 2
• Filter performance: Regular evaluation (though no consensus on specific monitoring strategies) 1
• Watch for CRRT-induced hypokalemia and hypophosphatemia (especially with high-dose or prolonged therapy) 6, 7

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Discontinuation and Transition Criteria

Consider transitioning from CRRT to intermittent hemodialysis when vasopressor support has been discontinued, hemodynamic stability achieved, intracranial hypertension resolved, and positive fluid balance can be controlled by intermittent modalities. 1, 2, 4

Transition Algorithm

• Vasopressor support stopped 1, 2, 4
• Hemodynamic stability achieved 1, 2, 4
• Intracranial hypertension resolved (if applicable) 1, 2, 4
• Fluid balance controllable by intermittent hemodialysis 1, 2, 4

Discontinuation Criteria

• Continue CRRT as long as criteria defining severe AKI are present 1
• Discontinue when kidney function has recovered or RRT becomes inconsistent with care goals 1
• Kidney recovery definition: Sustained independence from RRT for minimum 14 days 2

Critical Pitfall: Do not assume renal recovery based on normalized creatinine or BUN during CRRT; these values are artificially reduced by dialysis, not by kidney recovery. True assessment requires 24-hour urine collection for volume and creatinine/urea clearance after RRT discontinuation. 2

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Special Considerations for ECMO Patients

CRRT should be integrated with ECMO based on institutional expertise, as it is critical for preventing and managing fluid overload that impairs optimal ECMO function. 1, 3, 4

• CRRT prevents fluid overload that compromises ECMO efficacy 3, 4
• Integration requires institutional expertise and available technology 1, 4