Hemofiltration

Hemofiltration is a renal replacement therapy that removes water and solutes by convection across a semipermeable membrane, with replacement fluid added to restore volume and electrolytes. It is used mainly in intensive care for acute kidney injury and fluid overload, especially when patients are hemodynamically unstable.

In hemofiltration, blood passes through a hollow-fiber filter; a pressure gradient forces plasma water and dissolved solutes into the ultrafiltrate. Replacement fluid is infused either before (pre-dilution) or after (post-dilution) the filter. Pre-dilution lowers filtration efficiency, while post-dilution increases clearance but raises the risk of hemoconcentration. Clearance can be combined with diffusion in hybrid CRRT modes such as CVVHDF. Therapy is delivered continuously.

Indications include acute kidney injury, refractory hyperkalemia, severe fluid overload, uremic symptoms, and toxin removal; it is often used in critically ill patients requiring gradual, continuous control of solute balance and volume.

Procedure: requires vascular access, typically a central venous catheter. The circuit includes a pump, hemofilter, and replacement fluid. Anticoagulation (systemic heparin or regional citrate) is common to prevent clotting. Net ultrafiltration rates typically 20–35 mL/kg/h, with therapy run 24 hours a day.

Advantages and limitations: offers gentle, continuous clearance and improved hemodynamic stability but requires continuous equipment, anticoagulation, and monitoring; potential complications include hypotension, electrolyte disturbances, infection, and catheter issues.

Comparison: Hemofiltration uses convection; intermittent hemodialysis relies on diffusion. CRRT encompasses CVVH, CVVHD, and CVVHDF; the choice depends on patient condition.