Acute renal failure is a commonly occurring problem in the care of intensive care unit (ICU) patients. One method of improving the care of these complex patients is to use continuous renal replacement therapies (CRRTs), of which continuous venovenous hemofiltration with dialysis (CVVHD) is one of the more common forms. This technique has the same indications as traditional dialysis (hyperkalemia, refractory acidosis, fluid overload, and symptomatic azotemia), but CVVHD supposedly is a gentler, more physiologic procedure to achieve solute and fluid clearance and may be particularly useful for those patients with hemodynamic instability. While this is the commonly accepted dogma in critical care, it is important to recognize that there is currently no literature that demonstrates a survival advantage in CRRT when compared with intermittent hemodialysis.

A simplified, schematized version of the mechanics of CVVHD is shown in Figure 244.1. There are several steps to be completed when initiating CVVHD. First, the placement of a double-lumen, large-bore central venous catheter (e.g., Shiley) for access is accomplished. Next, blood from this catheter is withdrawn at approximately 150 to 200 mL/min by a pump and passed through a filter with multiple layers of a semipermeable membrane. This membrane allows for the diffusion of fluid and solute across the membrane with the resulting formation of a filtrate that is normally clear in appearance. Finally, the blood flows back to the patient from the other end of the filter by a venous return line that in most systems has a trap for clots and an air detector. This line is reconstituted with a crystalloid solution that mimics the composition of plasma. It is a necessity that the blood flow in the dialysis circuit continues without stagnation so that clots do not form. Anticoagulation is usually administered either through the use of heparin or citrate-containing replacement fluids to ensure an adequate blood flow.