As is known, for various reasons, it may prove necessary to supplement or replace the renal function of patients to remove waste liquids and soluble substances, such as substances administered to the patient and/or waste substances contained in the blood as a result of pathology, surgery, etc.
Various procedures are employed for this purpose, including haemodialysis, haemofiltration and ultrafiltration, all of which provide for removing waste products from the patient. That is, the patient's blood is fed through filters or membranes to eliminate the waste substances in it, and is then fed back to the patient.
For patients in grave conditions, procedures include Continuous ArterioVenous Haemofiltration (CAVH), Continuous VenoVenous Haemofiltration (CVVH), or, in general, CRRT as defined above. In this type of procedure, the patient is connected permanently to the haemofiltration machine for a prolonged period of time.
Examples of known CRRT machines are described in U.S. Pat. No. 5,211,849 and U.S. Pat. No. 6,349,170. That is, a CRRT machine comprises a central unit connected at the input and output to the patient, e.g. by means of one or more catheters inserted inside corresponding blood vessels, to continuously withdraw the blood for treatment and feed back the treated blood. The central unit of a CRRT machine normally comprises a blood pump, blood heating and processing means, such as, heparin adding means, means for feeding refill liquid into the blood, and a haemofilter. The blood withdrawn continuously from the patient is thus pumped by the blood pump along the machine circuit, heparin and appropriately heated refill liquid is added, and the blood is then filtered before being fed back to the patient.
A major drawback of currently used CRRT systems is their slow speed in relation to patient requirements.
Another drawback of known CRRT systems is the compulsory use of a pump for the ultrafiltrate, which is less tolerable by chronic, haemodynamically unstable patients whose refill capacity is always unknown.
Furthermore, the known CRRT machine are relatively complex and comprising a lot of elements.