Dialysis machine
A dialysis machine or hemodialysis machine enables the patient-specific removal of dissolved substances (e.g. urea , creatinine , vitamin B12 or β2-microglobulin ) and, if necessary, a defined proportion of water from the blood for renal replacement treatments (see dialysis ). Dialysis machines are used for both hemodialysis and hemodiafiltration .
Dialysis machines consist of various technical modules that can basically be divided into two different functional areas. In the case of devices for chronic dialysis, water treatment and the provision of dialysate as well as their balancing are an essential functional area (hydraulics). In acute dialysis devices, this function is provided by providing dialysis solutions (solution bags). These devices do not contain hydraulics. The second functional area is blood circulation, i. H. pumping the blood through an extracorporeal blood circuit by means of an extracorporeal blood pump past the filter membrane (dialyzer, hemofilter), there are 1-, 2- and 4-pump systems. This is always a combination of the device (extracorporeal blood module) and the suitable blood tubing system (disposable item).
The heart of a dialysis treatment is the dialyzer , in which the exchange of substances between blood and dialysate takes place through a semi-permeable membrane of 1.2 to 1.8 m². The dialysis machine thus “only” provides the framework conditions to carry out a dialysis treatment.
Both the dialysate and the extracorporeal blood circulation are made up of several units that are used for pre-treatment and post-processing. On the dialysate side, the pure water produced in special water treatment systems is first heated to physiological temperatures in the dialysis machine in order to avoid hypothermia or overheating of the patient. Additional degassing is used to avoid gas bubbles in the liquid, which can accumulate in the dialyzer at negative pressure and thus reduce the effectiveness of the exchange of substances.
The dialysate is produced from this pretreated pure water with the addition of electrolytes and, if necessary, glucose , the composition and the amount of the electrolytes usually being tailored to the individual needs of the patient.
A greater technical effort is required for the regulation of the ultrafiltration rate, since with values of a maximum of 10 ml / min it only accounts for a fraction of the total dialysate flow of about 500 ml / min. There are various more or less complex technical systems for this, for example the tank recirculation system or the semi-single-pass system, which allow continuously controlled ultrafiltration. This is generally done by subtracting the desired rate from the overall system using a pump. The resulting negative pressure regulates the transmembrane pressure and thus also the ultrafiltration rate in the dialyzer.
Modern dialysis machines contain a complex safety system that protects the patient and the user from incorrect operation and faulty device function and, if necessary, interrupts the treatment.
The extracorporeal blood circuit essentially consists of an arterial and a venous tube system, with the dialyzer in between. There are usually in the arterial hose system
- a dispensing point for medication
- a pressure transducer unit for arterial pressure measurement (pressure in front of the filter)
- a pump hose that is inserted into the blood pump ( hose pump ) and conveys the blood.
- a hose connection for adding heparin ( e.g. heparin syringe )
- a bubble trap to trap air bubbles in the arterial tube segment
The venous tube system (after the dialyzer), which returns the blood to the patient, usually contains:
- a bubble catcher
- a pressure sensor unit for venous pressure measurement (pressure after the filter)
- an air detector to detect air in the hose system
- a shut-off clamp to clamp off the patient venously in the event of a fault
An alternative to heparin is citrate and calcium anticoagulation , which requires additional elements in the hose system and components on the device (see citrate anticoagulation ).
Various measuring and monitoring devices are integrated into the dialysis machine to ensure that treatment is safe for the patient. For example, the blood leakage in the dialyzer is checked by measuring the cloudiness of the dialysate using optical methods. In addition, sensors are used to measure temperature, pressure, volume flow and conductivity .
Modern dialysis machines also allow patient-specific profiles with z. B. over the duration of a dialysis treatment varying dialysate composition or with a likewise time-varying ultrafiltration rate, which is based on the measured relative blood volume of the patient.
First artificial kidney 1913 by JJ Abel, LG Rountree and BB Turner (replica)
First artificial kidney used in humans in 1924 by Georg Haas (replica)
First artificial kidney successfully used in humans by Willem Kolff in 1945 (replica)
Moeller kidney type III from 1955
Plate dialyzer according to Frederik Kiil
“Stuttgart kidney” from 1970
literature
- Amitava Majumder, Anne Paschen: Medical working techniques. In: Jörg Braun, Roland Preuss (Ed.): Clinic Guide Intensive Care Medicine. 9th edition. Elsevier, Munich 2016, ISBN 978-3-437-23763-8 , pp. 29–93, here: pp. 60–66 ( dialysis ).
