As the kidney is a sensitive organ, it can temporarily lose its function during a serious illness, for example due to fluctuations in blood pressure or a lack of fluids. It often recovers as soon as the illness is over. To bridge this time, a machine is used that takes over the function of the kidney. Blood is aspirated via a catheter, purified by a complex filter system and returned to the circulatory system. This requires access to the large veins. Most patients tolerate this well. A local anesthetic is required for the insertion.