Continuous haemofiltration in the intensive care unit

Abstract

Continuous renal replacement therapy (CRRT) was first described in 1977 for the treatment of diuretic-unresponsive fluid overload in the intensive care unit (ICU). Since that time this treatment has undergone a remarkable technical and conceptual evolution. It is now available in most tertiary ICUs around the world and has almost completely replaced intermittent haemodialysis (IHD) in some countries. Specially made machines are now available, and venovenous therapies that use blood pumps have replaced simpler techniques. Although, it remains controversial whether CRRT decreases mortality when compared with IHD, much evidence suggests that it is physiologically superior. The use of CRRT has also spurred renewed interest in the broader concept of blood purification, particularly in septic states. Experimental evidence suggests that this is a promising approach to the management of septic shock in critically ill patients. The evolution and use of CRRT is likely to continue and grow over the next decade.

Figure 1

A `makeshift' CRRT circuit, using a simple and inexpensive blood pump with pressure alarms and air trap. Ultrafiltration is controlled using standard ICU-type volumetric pumps. Replacement fluid administration is similarly controlled.

Figure 2

The design of a CVVHD circuit using a simple blood pump, volumetric pumps for dialysate control and a double lumen catheter for vascular access.

Figure 3

Prisma CRRT machine (Hospal, Lyon, France). This is from a new generation of devices that have been developed to be simple to operate and prime, and that possess more sophisticated alarm and monitoring functions.

Figure 4

Baxter BM 25 machine. This device was initially developed for intermittent haemofiltration. However, it has proven useful for continuous therapy. Although it does not have sophisticated graphic and alarm functions, it can achieve ultrafiltration rates of up to 10 l/h. This ability to achieve high ultrafiltrate rates makes this device ideal for high-volume haemofiltration therapy.