Hemodialysis
A dialysis machine allows the patient-specific removal of dissolved substances (such as urea, creatinine, B12 and β2 -microglobulin ), and optionally of a defined proportion of water from the blood of renal replacement treatments (see dialysis). Dialysis equipment be used for both hemodialysis and hemodiafiltration.
Dialysis machines are made of different technical modules which can be basically divided into two functional areas. For devices for chronic dialysis water treatment and the provision of dialysate and their accounting are an essential functional area ( hydraulics). For devices for acute dialysis, this function is provided by the provision of dialysis solutions ( solution bag ). This equipment contains no hydraulics. The second functional region is the blood flow, that is, pumping the blood through an extracorporeal blood circulation to the filter membrane over ( dialyzer ). It always is a combination of device ( extracorporeal blood module ) and the appropriate blood tubing system ( disposable).
The heart of a dialysis treatment represents the dialyzer, which takes place through a semipermeable membrane from 1.2 to 1.8 m of material exchange between blood and dialysate. The dialysis unit is thus "only" the conditions available to perform a dialysis treatment.
Both the dialysate and the extracorporeal blood circuit are composed of several units that serve the pre-treatment or follow-up. Dialysate is first heated in the dialysis machine, the pure water produced in special water treatment plants to physiological temperatures so as to avoid supercooling ( hypothermia ) or overheating of the patient. An additional degassing is used to avoid gas bubbles in the liquid in the dialyzer can accumulate at vacuum and would thus reduce the effectiveness of mass transfer.
The dialysate is prepared from this pre-treated with the addition of clean water and optionally electrolytes from glucose, wherein in general, the composition and the amount of the electrolyte to be aligned to the individual needs of the patient.
A greater technical effort is required for the regulation of the ultrafiltration rate, since this makes only minutes with values of at most 10 ml / Gesamtdialysatflusses of a fraction of about 500 ml / min. This is done with various more or less complex technical systems, such as the tank recirculation system or the semi- single-pass system, which allow a continuous controlled ultrafiltration. This is generally done by deducting the desired rate from the entire system by a pump. The resulting negative pressure regulates the transmembrane pressure and hence the rate of ultrafiltration in the dialyser.
Modern dialysis machines include a complex security system that protects the patient and the user from operator error and faulty equipment function and optionally interrupts the treatment.
The extracorporeal blood circuit consists essentially of an arterial and a venous tube system sits in between the dialyzer. In the arterial line system are usually
- A feed point for drugs
- A pressure transducer unit for arterial pressure measurement ( pressure upstream of the filter)
- A pump tube which is placed in the blood pump ( peristaltic pump ) and promotes the blood.
- A hose connection for a heparin addition ( for example, heparin syringe )
- A bubble trap for trapping bubbles in the arterial tube segment
The venous tubing (after the dialyzer ) which feeds the blood back to the patient, typically comprises:
- A bubble trap
- A pressure transducer unit for venous pressure measurement ( pressure after the filter )
- An air detector for detecting air in the tubing system
- A shut-off clamp to pinch the patient in case of error venous
An alternative to heparin represents the citrate and calcium anticoagulation requires the additional elements in the tube system and components on the device ( see Citratantikoagulation ).
To ensure a safe treatment for the patient various measurement and monitoring devices are integrated into the dialysis machine. So, for example, checking the blood leakage occurs in the dialyzer by measuring the turbidity of the dialysate by means of optical methods. In addition, sensors are used for temperature, pressure, flow rate and conductivity measurement.
Modern dialysis machines also allow the shutdown of patient-specific profiles with, for example, over the duration of a dialysis treatment varying dialysate or a similarly time-varying ultrafiltration rate, which is based on the measured relative blood volume of the patient.