In a critically ill, hemodynamically unstable patient with acute kidney injury (AKI) and oliguria/anuria, how should continuous venovenous hemofiltration (CVVH) be initiated and managed, including blood flow rate, replacement fluid dose, anticoagulation strategy, ultrafiltration targets, and electrolyte/acid‑base monitoring?

Continuous Venovenous Hemofiltration (CVVH) in Critically Ill Patients with AKI

In hemodynamically unstable patients with acute kidney injury, initiate CVVH with a target effluent dose of 20–25 mL/kg/h, using regional citrate anticoagulation as first-line, bicarbonate-buffered replacement fluid, right internal jugular vascular access, and blood flow rates of 100 mL/min or higher, while monitoring delivered dose frequently because prescribed dose often falls short of actual delivery. 1, 2

Vascular Access Strategy

Site selection follows a strict hierarchy:

• First choice: Right internal jugular vein 1, 2
• Second choice: Femoral vein (though inferior in obese patients) 1, 2
• Third choice: Left internal jugular vein 1, 2
• Last resort: Subclavian vein (avoid due to thrombosis and stenosis risk) 1, 2

Technical requirements:

• Use an uncuffed, nontunneled dialysis catheter of appropriate length and gauge 1, 2
• Always employ ultrasound guidance for insertion 2
• Obtain chest radiograph immediately after internal jugular or subclavian placement before first use 2
• Use biocompatible membrane dialyzers 2

Blood Flow Rate and Circuit Management

Set blood flow rate at 100 mL/min or higher regardless of systemic blood pressure 3, 4. This pump-driven approach eliminates dependence on patient hemodynamics and reduces risks associated with arterial cannulation. 4

Pre-dilution strategy should be employed when:

• Frequent filter clotting occurs 1, 2
• Blood flow limitations restrict extracorporeal clearance 1, 2
• High-volume CVVH is needed to enhance ultrafiltration rates 1, 2

Note that pre-dilution extends filter life but reduces solute clearance efficiency compared to post-dilution. 1

Replacement Fluid Dose and Monitoring

Target effluent volume: 20–25 mL/kg/h 1, 5, 2. This represents the combined total of ultrafiltrate and dialysate flow.

Critical monitoring requirement: The delivered dose frequently falls short of prescribed dose, requiring frequent assessment of actual effluent volume with prescription adjustments as needed. 1, 2 This is one of the most common pitfalls in CVVH management—do not assume the prescribed dose equals delivered dose. 2

Higher intensity dosing (>25 mL/kg/h) has not demonstrated mortality benefit in major trials (RENAL and ATN), so standard dosing is appropriate. 6

Anticoagulation Strategy

Regional citrate anticoagulation is first-line for patients without contraindications 1, 2. However, in the United States, FDA-approved citrate solutions for regional anticoagulation are not currently available, which limits this recommendation's applicability. 1

When citrate is used:

• Monitor closely for both metabolic alkalosis and metabolic acidosis 1, 2
• A validated system uses trisodium citrate/citric acid solution (113 mmol/L citrate) at 250 mL/h with blood flow of 75 mL/min, targeting post-filter ionized calcium of 0.23 mmol/L 7
• Use calcium-containing dialysate (1.81 mmol/L Ca) to avoid mandatory systemic calcium supplementation 7

Alternative anticoagulation options:

• Unfractionated heparin or low-molecular-weight heparin if citrate contraindicated 2
• Adjust heparin to prevent filter clotting rather than targeting a specific PTT (mean dose 6.5 U/kg/h in clinical studies) 4
• Direct thrombin inhibitors or Factor Xa inhibitors for heparin-induced thrombocytopenia 2
• Low-molecular-weight heparins require regular anti-factor Xa monitoring 1

Fluid Composition

Bicarbonate-buffered replacement solutions are mandatory 1, 2. Lactate-buffered solutions must be avoided, particularly in patients with:

• Circulatory shock 2
• Liver failure 1, 2
• Lactic acidemia 2

Lactate can worsen acidosis in these populations. 1

Additional fluid management principles:

• Avoid fluids with supra-physiologic glucose concentrations to prevent hyperglycemia 1, 2
• Ensure dialysate complies with AAMI standards for bacterial and endotoxin contamination 2
• Use integrated fluid-balancing systems rather than adapted IV pumps to reduce error risk 1, 2

Ultrafiltration Targets and Fluid Balance

Target net fluid removal of 100–200 mL/hour for volume-overloaded patients 3. Volume overload should be actively avoided, especially in patients with acute lung injury, as negative fluid balance decreases ICU length of stay in this population. 1, 2

The gradual, continuous nature of CVVH allows stable hemodynamic status during fluid removal, unlike intermittent hemodialysis. 3

Electrolyte and Acid-Base Monitoring

Dialysate and replacement fluid should contain physiologic electrolyte concentrations except in patients with extreme imbalances 1.

For acid-base control:

• Adjust dialysate bicarbonate concentration (typically 13–34 mmol/L) to control acid-base status and prevent hypernatremia 7
• Target normal base excess (achieved with mean dialysate bicarbonate of 26 mmol/L in validation studies) 7
• Monitor for citrate-associated metabolic derangements if using regional citrate anticoagulation 1, 7

Electrolyte losses require attention:

• CVVH causes continuous loss of amino acids, proteins, vitamins, trace elements, potassium, and phosphate 2
• Protein requirements increase to 1.5–1.7 g/kg/day due to continuous losses 5
• Initiate medical nutrition therapy for any ICU patient with AKI lasting >48 hours 2

Medication Dosing Considerations

Therapeutic drug monitoring is essential for beta-lactam antibiotics and other dialyzable medications 6, 2. Drug clearance varies with:

• Dialysate flow rate (higher rates increase elimination) 6
• Residual kidney function (significant impact when CrCl >50 mL/min) 6
• CVVH modality (piperacillin/tazobactam half-lives are significantly shorter with CVVHDF compared to CVVH alone) 6

Catheter Care and Infection Prevention

Do not use topical antibiotics at the insertion site 2. Standard sterile technique and proper site care are sufficient.

Do not use antibiotic lock solutions for infection prevention 2. These lack efficacy and promote resistance.

Transition and Discontinuation Criteria

Transition from CVVH to intermittent hemodialysis when:

• Vasopressor support has been stopped 1, 2
• Intracranial hypertension has resolved 1, 2
• Positive fluid balance can be managed with intermittent therapy 1, 2

Discontinue CVVH when:

• Sufficient renal recovery has occurred 1, 2
• Ongoing RRT no longer aligns with shared-care goals 1, 2

Common Pitfalls to Avoid

• Underdosing: Delivered dose often falls 20–30% below prescribed dose; assess actual effluent volume frequently 1, 2
• Subclavian access: Avoid due to thrombosis and stenosis risk 1, 2
• Lactate buffers: Never use in shock, liver failure, or lactic acidosis 1, 2
• Inadequate nutrition: Increase protein to 1.5–1.7 g/kg/day to compensate for continuous losses 5, 2
• Filter clotting: Consider pre-dilution if clotting occurs frequently 1, 2
• Drug dosing errors: Monitor dialyzable medications closely, especially beta-lactams 6, 2