In a hemodynamically unstable ICU patient with acute kidney injury and severe fluid overload, when should continuous renal replacement therapy be initiated and what are the recommended prescription parameters (modality, effluent dose, anticoagulation, and net fluid removal)?

CRRT in Hemodynamically Unstable ICU Patients with AKI

Initiation Timing

For hemodynamically unstable ICU patients with AKI and severe fluid overload, initiate CRRT when metabolic and fluid demands exceed kidney capacity, specifically when vasopressor-dependent hypotension prevents safe intermittent hemodialysis, or when life-threatening complications develop including severe hyperkalemia with ECG changes, refractory metabolic acidosis, pulmonary edema unresponsive to diuretics, or uremic complications. 1, 2

Clinical Triggers for CRRT Initiation:

• Hemodynamic instability requiring vasopressors - CRRT provides superior hemodynamic tolerance compared to intermittent modalities 1, 2
• Severe fluid overload when positive fluid balance cannot be managed by intermittent hemodialysis 2
• Acute brain injury or increased intracranial pressure - CRRT reduces risk of cerebral edema and ICP fluctuations 1, 2
• Severe hyperkalemia with ECG changes (peaked T waves, widened QRS, bradycardia) 3
• Refractory metabolic acidosis with impaired respiratory compensation 3
• Pulmonary edema unresponsive to diuretics 3
• Uremic complications (encephalopathy, pericarditis, bleeding) 3

Avoid Common Pitfalls:

• Do not rely solely on BUN and creatinine thresholds - consider the broader clinical context including hemodynamics, fluid status, and metabolic derangements 2
• Do not delay CRRT in cardiac patients with reduced ejection fraction - these patients have severely limited fluid tolerance and rapid deterioration risk 4

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CRRT Modality Selection

Use continuous venovenous hemodiafiltration (CVVHDF) as the preferred modality, as it combines both diffusive and convective clearance mechanisms for optimal solute control. 3, 5

• CVVHDF provides superior management of both small and middle-molecular-weight solutes 5
• For patients on ECMO or ventricular assist devices, integrate CRRT based on institutional expertise 2

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Effluent Dose Prescription

Deliver an effluent volume of 20-25 mL/kg/hour, which represents the evidence-based standard dose for CRRT in AKI. 2, 3, 6

Dosing Considerations:

• This dose (20-25 mL/kg/hour) has been validated in major trials and provides adequate solute control 2, 3
• Monitor prescribed versus delivered dose systematically - actual delivered dose often falls short of prescribed due to circuit downtime 6
• Higher doses (>25 mL/kg/hour) have not demonstrated mortality benefit and increase cost 6
• Adjust for high catabolic states, but avoid empiric dose escalation without clear indication 6

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Anticoagulation Strategy

Use regional citrate anticoagulation as first-line for patients without contraindications, as it provides superior circuit life and reduced bleeding risk compared to heparin. 1, 2, 3

Anticoagulation Algorithm:

For patients WITHOUT increased bleeding risk:

• First choice: Regional citrate anticoagulation 1, 2, 3
• Citrate provides anticoagulation in the circuit while minimizing systemic effects 1
• Contraindications include severe liver failure and severe lactic acidosis 1

For patients WITH increased bleeding risk:

• Still prefer regional citrate if no contraindications 1, 2
• Avoid regional heparinization in bleeding-risk patients 1, 2

For patients with heparin-induced thrombocytopenia (HIT):

• Use direct thrombin inhibitors (argatroban) or Factor Xa inhibitors 1, 2
• All heparin must be stopped immediately 1
• Argatroban preferred if no severe liver failure 1

For patients with citrate contraindications:

• Use unfractionated or low-molecular-weight heparin 1, 2

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Dialysate and Replacement Fluid Composition

Use bicarbonate-based (not lactate-based) dialysate and replacement fluid in all CRRT patients, particularly those with circulatory shock, liver failure, or lactic acidemia. 1, 2, 3

Buffer Selection Rationale:

• Bicarbonate is strongly recommended (Grade 1B) for patients with circulatory shock 1
• Bicarbonate is strongly recommended (Grade 2B) for patients with liver failure or lactic acidemia 1, 2
• Lactate-buffered solutions risk worsening acidosis in patients unable to metabolize lactate 1, 2

Electrolyte Management:

• Potassium bath: 0-1 mEq/L for severe hyperkalemia, 2 mEq/L for maintenance 3
• Calcium bath: 2.5 mEq/L 3
• Monitor electrolytes every 2-4 hours initially to prevent paradoxical disturbances (hypokalemia, hypophosphatemia) 3, 7

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Vascular Access

Insert an uncuffed nontunneled dialysis catheter using ultrasound guidance, with site selection prioritized as: right internal jugular vein (first choice), femoral vein (second choice), left internal jugular vein (third choice), and subclavian vein (last choice). 1, 2, 3

Access Protocol:

• Always use ultrasound guidance for insertion (Grade 1A recommendation) 1, 2
• Obtain chest radiograph before first use of internal jugular or subclavian catheters 1, 2
• Avoid subclavian veins due to high risk of thrombosis and stenosis that can compromise future access 2, 3
• Do not use topical antibiotics or antibiotic locks for infection prevention in nontunneled catheters 1

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Net Fluid Removal Strategy

Target controlled, gradual fluid removal at rates that maintain hemodynamic stability, avoiding rapid ultrafiltration that can precipitate hypotension and worsen organ perfusion. 2, 4

Fluid Removal Guidelines:

• In cardiac patients with reduced ejection fraction, use CRRT for precise fluid control rather than attempting fluid boluses 4
• Limit ultrafiltration rate to <13 mL/kg/hour to avoid intradialytic hypotension 3
• Reassess fluid status every 6-12 hours for signs of ongoing overload or excessive removal 4
• Monitor hourly vital signs and urine output (target >0.5 mL/kg/hour if residual function) 3, 4

Critical Caveat for Cardiac Patients:

• Avoid fluid boluses entirely in patients with CHF and reduced ejection fraction - even small boluses (250 mL) can precipitate acute pulmonary edema 4
• CRRT allows aggressive nutritional and inotropic support without exacerbating fluid overload 8

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Monitoring During CRRT

Implement systematic monitoring of hemodynamics, electrolytes, acid-base status, and circuit function to ensure safe and effective CRRT delivery. 3, 6, 5

Monitoring Protocol:

• Hourly vital signs and assessment for hypotension 3
• Electrolytes and acid-base status every 2-4 hours initially, then every 6-12 hours once stable 3, 7
• Pre- and post-treatment weights 3
• Prescribed versus delivered effluent dose - this is a critical quality indicator 6
• Filter performance and circuit patency 2
• Drug levels for renally cleared medications requiring dose adjustment 9, 5

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Transition to Intermittent Therapy

Consider transitioning from CRRT to intermittent hemodialysis when vasopressor support has been discontinued, hemodynamic stability achieved, intracranial hypertension resolved (if applicable), and positive fluid balance can be adequately controlled by intermittent sessions. 2

Transition Criteria:

• Hemodynamic stability without vasopressors 2
• Resolution of acute brain injury or elevated ICP 2
• Ability to tolerate fluid shifts with intermittent therapy 2
• Adequate solute control achievable with 3-4 hour sessions 1

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Multidisciplinary Considerations

Coordinate CRRT management with nutrition support, physical rehabilitation, and pharmacy for drug dosing adjustments to optimize patient outcomes. 9, 5

• CRRT enables aggressive nutritional support without worsening azotemia 8, 9
• Many medications require dose adjustment during CRRT 9, 5
• Early mobilization and physical therapy should continue when feasible 9
• Implement CRRT quality assurance programs to monitor delivery metrics 6, 9, 5