Severely ill patients admitted to the intensive care unit may develop an acute failure of kidney function. Renal function generally recovers if the acute illness improves. To bridge this period, renal function is temporarily replaced by continuous hemofiltration, so called continuous venovenous hemofiltration (CVVH). To remove toxic substances and fluids, the patient's blood flows through a circuit, containing a filter. Flow in the filter is regulated by the CVVH-device.