The continuous renal replacement therapies (CRRTs) comprise a spectrum of treatments that include both hemofiltration (convection-based solute and water removal) and hemodialysis (diffusion-based solute removal) techniques [1,2]. (See "Continuous renal replacement therapies: Overview".)
These techniques have gained favor in the treatment of critically ill patients with renal failure primarily because of improved hemodynamic stability compared with intermittent hemodialysis. Although some investigators have suggested that the use of CRRT is associated with improved outcomes in acute renal failure (ARF), this has not yet been demonstrated by prospective randomized trials.
CRRT techniques initially utilized arteriovenous extracorporeal circuits, in which blood flow was driven by the gradient between the mean arterial pressure (MAP) and venous pressure. Continuous venovenous hemodialysis (CVVHD) was developed in the mid-1980s as an alternative to continuous arteriovenous hemofiltration (CAVH) and continuous arteriovenous hemodialysis (CAVHD) . The use of a pump-driven venovenous circuit in CVVHD permits blood flows that are both higher and more constant than provided by an arteriovenous circuit. In addition, the elimination of the need for a large-bore arterial catheter eliminates the associated risks of arterial thrombosis and arterial bleeding [4,5].
The technical aspects of performing CVVHD are reviewed here. General discussions of CRRT and the technical aspects of other modalities are presented separately. (See "Continuous arteriovenous hemodialysis: Technical considerations" and "Continuous renal replacement therapy in acute kidney injury (acute renal failure)".)
Angioaccess in continuous venovenous hemodialysis (CVVHD) is generally achieved using a standard double-lumen hemodialysis catheter (figure 1). Blood flow through the extracorporeal circuit is driven by a blood pump, with rates usually maintained between 100 and 250 mL/min. Dialysate is perfused through the hemofilter/hemodialyzer, countercurrent to the direction of blood flow.