In an adult ICU patient who is intubated, on vasopressors, with rising serum creatinine, oliguria (<0.5 mL/kg/h) and positive fluid balance, should continuous renal replacement therapy be initiated now, and what are the recommended prescription, anticoagulation, vascular access, monitoring, and criteria for transition to intermittent dialysis?

CRRT Initiation and Management in Hemodynamically Unstable ICU Patients

Should CRRT Be Initiated Now?

Yes, initiate CRRT immediately in this hemodynamically unstable patient on vasopressors with oliguria and positive fluid balance. CRRT is preferentially indicated over intermittent hemodialysis for patients with AKI who have hemodynamic instability requiring vasopressor support 1, 2. The combination of vasopressor dependence, oliguria, and positive fluid balance represents the classic scenario where CRRT provides superior hemodynamic tolerance, better fluid control, and slower solute shifts compared to intermittent modalities 1, 3.

Key Indications Present in This Patient

• Hemodynamic instability on vasopressors: This is the primary indication for CRRT over intermittent hemodialysis, as CRRT offers greater hemodynamic stability and better tolerance of fluid removal 1, 2
• Oliguria (<0.5 mL/kg/h): Represents severe AKI requiring renal replacement therapy 1
• Positive fluid balance: CRRT provides superior continuous fluid control, critical since volume overload >10-15% body weight is associated with adverse outcomes and delayed renal recovery 4, 2
• Intubated status: Allows for the continuous nature of therapy without patient discomfort concerns 3

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CRRT Prescription Parameters

Effluent Dose

Prescribe an effluent dose of 25-30 mL/kg/h to achieve a delivered dose of 20-25 mL/kg/h, accounting for typical 15-20% loss due to downtime and circuit interruptions 2, 5. This dosing is based on evidence showing adequate solute control without additional mortality benefit from higher doses 2, 5.

Modality Selection

• Continuous venovenous hemodiafiltration (CVVHDF) combines both diffusive and convective clearance, providing optimal solute control 3, 6
• Alternatively, continuous venovenous hemofiltration (CVVH) with pre-dilution can be used to increase ultrafiltration rates and reduce filter clotting risk 2

Replacement Fluid Composition

Use bicarbonate-based replacement fluids exclusively and avoid lactate-based solutions 2, 7. This is critical in hemodynamically unstable patients, those with shock, liver failure, or lactic acidosis, as lactate-containing solutions may exacerbate acidosis 2, 7. Formulate with physiologic electrolyte concentrations and avoid supraphysiologic glucose to reduce hyperglycemia risk 2.

Blood Flow Rate

Target blood flow rate of 150-200 mL/min with hourly monitoring of circuit pressures and effluent rate 2.

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Anticoagulation Strategy

First-Line: Regional Citrate Anticoagulation

Regional citrate anticoagulation is the first-line choice unless contraindicated 2, 8. Citrate extends filter lifespan and lowers bleeding risk compared to systemic heparin 2, 5.

Contraindications to citrate include:

• Severe liver failure or shock liver 2, 8
• High risk of citrate accumulation 2
• Severe lactic acidosis 2

Alternative: Unfractionated Heparin

When citrate is contraindicated, use unfractionated heparin with aPTT monitoring to maintain therapeutic anticoagulation 2. Avoid low-molecular-weight heparin due to accumulation risk in AKI 2.

Special Situations

• For heparin-induced thrombocytopenia: Use direct thrombin inhibitors (argatroban) or Factor Xa inhibitors 2
• For patients with increased bleeding risk: Consider minimal or no anticoagulation 7

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Vascular Access

Site Selection (in order of preference):

1. Right internal jugular vein (first choice) 2, 7
2. Femoral vein (avoid in obese patients) 2
3. Left internal jugular vein 2, 7
4. Subclavian vein ONLY as last resort due to high thrombosis/stenosis risk 2, 7

Catheter Type and Insertion

• Use an uncuffed nontunneled dialysis catheter for acute CRRT initiation 2
• Use a cuffed dialysis catheter only when prolonged RRT (>2-3 weeks) is anticipated 2
• Always use ultrasound guidance for catheter insertion 1, 2
• Obtain chest radiograph before first use of internal jugular or subclavian catheters to confirm placement 1, 2

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Monitoring Requirements

Hourly Monitoring

• Circuit pressures (replace filter when transmembrane pressure exceeds manufacturer limit) 2
• Blood flow rate (target 150-200 mL/min) 2
• Effluent rate 2
• Net fluid balance 2

Temperature Management

• Warm replacement fluids using inline fluid warmers 2
• Maintain patient core temperature >35°C to prevent hypothermia 2
• Check core temperature at least every 4 hours during CRRT 2

Laboratory Monitoring

• Assess electrolytes, acid-base status, and fluid balance regularly 2, 5
• Monitor serum urea, creatinine, and electrolytes (sodium, potassium, bicarbonate) at least every 48 hours or more frequently if clinically indicated 4

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Fluid Removal Strategy

Ultrafiltration Approach

• Implement integrated fluid-balancing systems specifically designed for CRRT rather than adapting standard IV pumps for improved precision 2
• Target net negative fluid balance cautiously, avoiding excessive dehydration that could delay renal recovery 4
• Remember that volume overload >10-15% body weight is associated with adverse outcomes 4, 2

Fluid Replacement During Therapy

• Use balanced crystalloids (lactated Ringer's) rather than 0.9% saline for any additional fluid administration to prevent metabolic acidosis and hyperchloremia 4, 7

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Criteria for Transition to Intermittent Hemodialysis

Consider transitioning from CRRT to intermittent hemodialysis when ALL of the following criteria are met:

1. Vasopressor support has been discontinued and hemodynamic stability achieved 2, 7
2. Resolution of any intracranial hypertension (if previously present) 2, 7
3. Fluid balance is controllable with intermittent therapy, typically <1-2 L positive per day 2
4. Patient can tolerate the 3-4 hour treatment duration without hemodynamic compromise 1

The transition should be gradual, with close monitoring during the first intermittent session to ensure adequate tolerance 1.

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Common Pitfalls to Avoid

• Do not interpret all AKI as "hypovolemic" requiring aggressive fluid resuscitation before CRRT initiation; this patient on vasopressors with positive fluid balance likely has euvolemia or hypervolemia 4
• Avoid subclavian venous access except as absolute last resort due to high thrombosis risk 2, 7
• Do not use lactate-buffered solutions in hemodynamically unstable patients or those with potential liver dysfunction 2, 7
• Do not rely solely on BUN and creatinine thresholds for CRRT decisions; consider the broader clinical context of hemodynamic instability and fluid overload 2
• Avoid excessive fluid removal that could worsen renal perfusion and delay recovery 4

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Special Considerations for This Patient

If on ECMO

Integrate CVVH into the ECMO circuit according to institutional protocols, coordinating anticoagulation management with the ECMO team, as anticoagulation is usually handled through the ECMO circuit itself 2.

Nutritional Support

Recognize that CRRT causes loss of amino acids and proteins in the dialysate, contributing to hypermetabolism 1. Ensure adequate nutritional support is provided during therapy 1, 5.