Extracorporeal Dialysis or Haemodialysis
In order to perform haemodialysis, the patient’s blood is introduced into an artificial kidney which, by means of a specific pump system, circulates the blood through a filter that cleanses it prior to returning it to the patient. The blood therefore needs to be extracted from the patient.
In urgency cases, this procedure is performed by placing a catheter inside a large calibre venous vessel (central venous catheter), whereas, when it is possible to select and programme an alternative treatment, an arteriovenous fistula is usually set up. This fistula is a point of junction surgically created in local anaesthesia between a vein and an artery, typically at the forearm level. At the beginning of the dialysis session, the patient is connected to the haemodialysis device via the central venous catheter or by introducing two needles at the level of the fistula.
The session usually lasts about four hours and is performed three times a week. The duration of each session and the weekly frequency may vary to the doctor’s discretion based on the patient’s clinical needs.
The central point of the treatment is a biocompatible dual-compartment element named ‘dialysis filter’. The blood extracted from the patient flows into the first compartment, while an aqueous solution called ‘dialysis solution’ is introduced into the second compartment. This solution is enriched with solutes that need to be released into the blood and is deficient in (or completely lacking) those that need to be removed. To allow for an adequate purification, the blood is kept flowing through the filter by means of a pump, at a flow rate of about 250 to 300 ml/min.
The total amount of liquids that need to be removed during a dialysis session depends on the patient’s intake of fluid between two consecutive sessions and is established by weighing the patient at the end of one dialysis session and at the beginning of the following one. The ‘ideal weight’ for the patient, called ‘dry weight’, is defined by the Nephrologist who performs the treatment, on the basis of clinical and instrumental data.