Continuous renal replacement therapy (CRRT) is an extracorporeal purification therapy used to treat patients who suffer from acute renal failure. Unlike the more traditional hemodialysis, CRRT is administered around the clock, providing patients with continuous therapy and sparing them the destabilizing hemodynamic and electrolytic changes characteristic of traditional hemodialysis. For patients who can’t tolerate traditional hemodialysis—such as those who have hypotension—CRRT is often the only choice for treatment.

The techniques used vary in complexity. Slow continuous ultrafiltration uses arteriovenous access and the patient’s blood pressure to circulate blood through a hemofilter. Because the goal of this therapy is the removal of fluids, the patient doesn’t receive any replacement fluids. Continuous venovenous hemofiltration (CVVH) uses a double-lumen catheter to provide access to a vein, and a pump moves blood through the hemofilter. Continuous venovenous hemodialysis (CVVH-D) uses a vein to provide the access while a pump moves dialysate solution concurrently with blood flow; this process continuously removes fluid and solutes. Slow extended daily dialysis (SLEDD) is a modification of traditional intermittent hemodialysis. SLEDD is usually performed in 6- to 12-hour treatment sessions, 5 to 7 days each week. The blood flow rates range from 100 to 250 mL/minute, resulting in an extended dialysis time and decreased solute rate and ultrafiltration.

For treatment of critically ill patients, CVVH, CVVH-D, and SLEDD are used instead of continuous arteriovenous hemofiltration (CAVH). CVVH, in particular, has several advantages over CAVH: It doesn’t require arterial access, it can be performed in patients with low mean arterial pressures, and it has better solute clearance than CAVH.