Extracorporeal Removal of Drugs: Continuous Renal Replacement Therapy

Continuous renal replacement therapy, or CRRT, is a vital treatment for patients with severe kidney dysfunction.

Unlike intermittent methods, CRRT continuously removes fluid and toxins from the bloodstream, using the patient's blood pressure or a pump to drive filtration through a specialized filter.

There are two main types of CRRT : continuous veno-venous hemofiltration or CVVH and continuous arteriovenous hemofiltration or CAVH.

CVVH involves placing a filter between veins such as the femoral or jugular, with a pump used to achieve higher filtration rates.

CAVH places a filter between the femoral artery and vein, and drug removal in this method depends on the sieving coefficient, S. When S equals one, the drug passes freely through the membrane. When S is less than one, the drug shows partial clearance, with some quantity retained in the plasma.

Clearance equals the sieving coefficient times the ultrafiltration rate. The amount of drug removed per unit time equals plasma concentration times the unbound fraction times the ultrafiltration rate.

Both methods require careful monitoring and include heparin to prevent clotting.