CVVHDF

CVVHDF, or continuous veno-venous hemodiafiltration, is a form of continuous renal replacement therapy used in critical care to remove waste products and excess fluid in patients with acute kidney injury or fluid overload. It combines features of both diffusion and convection to clear solutes across a semipermeable membrane.

In CVVHDF, blood is drawn from the patient through a vascular access catheter and circulated by a pump through a hemofilter. Dialysate flows on the opposite side of the membrane to promote diffusion, while replacement fluid may be added pre-filter (pre-dilution) or post-filter (post-dilution) to enhance convective clearance. The machine controls the blood flow, dialysate flow, and ultrafiltration rate, which determines the net fluid removal. The effluent stream contains the combined dialysate and ultrafiltrate and is discarded.

Indications for CVVHDF include acute kidney injury with oliguria or anuria, fluid overload, severe acid-base or electrolyte disturbances, and situations requiring continuous, gentle removal of toxins and fluids in hemodynamically unstable patients. Anticoagulation is commonly used to prevent circuit clotting, with options such as regional citrate anticoagulation or systemic heparin.

Compared with other CRRT modalities, CVVHDF provides solute clearance through both diffusion and convection, potentially enhancing removal of a wide range of molecular weights. Limitations include the need for specialized equipment and trained personnel, risks of bleeding with anticoagulation, infection, and electrolyte shifts.