CVVHD

CVVHD, or Continuous Veno-Venous Hemodialysis, is a modality of continuous renal replacement therapy (CRRT) used to support kidney function in critically ill patients. It provides sustained solute and fluid removal through diffusion across a semipermeable membrane in the intensive care setting.

In CVVHD, blood from the patient is circulated through a circuit and passes the membrane where solutes diffuse into a countercurrent dialysate. Solute clearance relies on diffusion rather than convection, and ultrafiltration removes plasma water that is discarded as effluent. The dialysis fluid composition can be adjusted to influence electrolyte balance and acid-base status, and the overall clearance is described by the effluent flow rate.

A CRRT machine, a hemofilter, and vascular access via a central venous catheter are used. Anticoagulation, typically heparin or regional citrate, is often employed to prevent circuit clotting. Dosing is expressed as effluent flow, commonly targeted around 20-25 ml/kg/h, and is adjusted to the patient’s needs and tolerance.

Indications include acute kidney injury in patients who are unstable for intermittent dialysis, toxin removal, and disturbances of electrolytes or acid-base balance that require continuous therapy.

Advantages include gradual fluid and solute removal, which can improve hemodynamic tolerance compared with intermittent therapies. Limitations involve dependence on anticoagulation, risk of circuit clotting and infection, higher resource use, and access to compatible fluids and filters. CVVHD is one of several CRRT modalities and is chosen based on patient factors and institutional protocols. Historically, it emerged in the late 20th century as CRRT evolved to support critically ill patients with kidney failure.