Figure 1.

Schematics of modes of continuous kidney replacement therapy. (A) Slow continuous ultrafiltration (SCUF): blood in the extracorporeal circuit is perfused through a hemofilter and an ultrafiltrate is generated equal to the desired rate of fluid removal. (B) Continuous venovenous hemofiltration (CVVH): blood in the extracorporeal circuit is perfused through a hemofilter and a high volume of ultrafiltrate is generated. Ultrafiltrate volume in excess of the desired rate of fluid removal is replaced with crystalloid solution that may be infused prior to the hemofilter (prefilter replacement fluid), into the return line (postfilter replacement fluid), or both. The net ultrafiltration rate is equal to the difference between the effluent and the replacement fluids flow rates. (C) Continuous venovenous hemodialysis (CVVHD): blood in the extracorporeal circuit is perfused through a hemodialyzer, dialysate is perfused across the membrane, and an ultrafiltrate is generated equal to the desired rate of fluid removal. The effluent consists of both the spent dialysate and ultrafiltrate with the net ultrafiltration rate equal to the difference between the effluent and dialysate flow rates. (D) Continuous venovenous hemodiafiltration (CVVHDF): blood in the extracorporeal circuit is perfused through a hemofilter, dialysate is perfused across the membrane, and a high volume of ultrafiltrate is generated. Ultrafiltrate volume in excess of the desired rate of fluid removal is replaced with crystalloid solution that may be infused before the hemofilter (prefilter replacement fluid), into the return line (postfilter replacement fluid), or both. The effluent consists of both the spent dialysate and ultrafiltrate with the net ultrafiltration rate equal to the difference between the effluent flow rate and the sum of dialysate and replacement fluid flow rates.