Techniques available

Renal support in intensive care varies substantially between units. In the early days of intensive care, renal support was limited to either haemodialysis or peritoneal dialysis. Advances in membrane technology led to the development of ‘continuous arteriovenous haemofiltration’ (CAVH). The driving pressure in this system is the patient's blood pressure; the blood is taken from an artery and returned to a vein. An ultrafiltrate of plasma water is produced, which is replaced by ‘replacement fluid’ that resembles plasma water but is devoid of the ‘unwanted’ molecules and ions, such as urea, creatinine and potassium. Fluid removal is achieved by replacing only a proportion of the volume of the fluid filtered. The development of CAVH enabled renal support to be undertaken on intensive care even in the absence of facilities for haemodialysis.

CAVH is now rarely used because of its problems, which include the dependence on systemic blood pressure, the need for large-bore arterial access and, even when running optimally, poor clearances. Some of these problems have been at least partly overcome by the development of the now most commonly used renal replacement technique used in the critically ill; ‘continuous veno-venous haemofiltration’ (CVVH).

Peritoneal dialysis has limited use in critically ill patients.