Renal replacement therapy (RRT) forms a very important part of the combined management of multiorgan failure along with mechanical ventilation and cardiovascular support:

• Severe acute renal failure (ARF) is a common complication in patients with multiorgan failure (10–20% of all critically ill patients) and 70% of these patients will require RRT [1, 2].

• In previous studies mortality rates have been reported to be as high as 33–93% [1, 2].

• In contrast, single organ ARF has a much lower-mortality rate — less than 10%.

RRTs

RRTs can be classified as continuous or intermittent. Units differ nationally as well as internationally regarding their preference of therapy. In Europe and Australia continuous renal replacement therapy (CRRT) predominates while in the USA intermittent replacement therapy (IRT) is preferred.

Haemofiltration (CRRT)

There are several methods of CRRT:

• Continuous veno-venous haemofiltration (CVVH) uses a double lumen venous cannula and a peristaltic pump which allows higher blood flows and increased membrane surface area, thus higher ultrafiltration rates and better uraemic control. CVVH produces an ultrafiltrate by maintaining a pressure difference over a highly permeable membrane (convection). Water is pushed across the membrane and carries dissolved solutes (known as solvent drag). A physiological substitution fluid is infused into the patient to maintain hydration status and chemical balance.