What is the working principle of a hemodialysis machine？
1. The principle of hemodialysis
Dialysis refers to the diffusion, permeation and ultrafiltration of the solution on both sides of the semipermeable membrane. The process of side flow finally reaches dynamic equilibrium. Hemodialysis achieves the purpose of treatment through solution dispersion and ultrafiltration between blood and dialysate. Therefore, the dialysis process is the process of dispersing and filtering the solute. Hemodialysis includes the movement of solutes and the movement of water, that is, blood and dialysate are exchanged in the dialyzer (artificial kidney) through semipermeable membrane contact and concentration gradient, so that metabolic waste and excessive electrolytes in the blood are transferred to the dialysate. Move, calcium ions and bases in the dialysate move to the blood. So as to remove the metabolic wastes and poisons in the patient's blood; adjust the water and electrolyte balance; adjust the acid-base balance. Has part of the functions of the human kidney (but cannot replace the endocrine and metabolic functions of the kidney).
2. Structure and working principle of hemodialysis machine
The hemodialysis machine can be roughly divided into two parts: the blood monitoring alarm system and the dialysate supply system. The blood monitoring alarm system includes blood pumps, heparin pumps, arteriovenous pressure monitoring and air monitoring, etc.; the dialysate supply system includes temperature control system, liquid dispensing system, degassing system, conductivity monitoring system, ultrafiltration monitoring and blood leakage monitoring, etc. Partial composition. Its working principle is: dialysis concentrate and dialysis water are prepared into qualified dialysate through the dialysate supply system, and through the hemodialyzer, it performs solute dispersion, permeation and ultrafiltration with the patient's blood drawn from the blood monitoring alarm system; after the effect The blood of the patient is returned to the patient through the blood monitoring alarm system, and the dialysis liquid is discharged from the dialysate supply system as a waste liquid; the continuous cycle is repeated to achieve the purpose of treatment and complete the entire dialysis process.
3. Functions of each part of the hemodialysis machine
(1). The blood monitoring alarm system part of the blood monitoring alarm system
a. Blood Pump: It is used to promote blood circulation to maintain the smooth progress of hemodialysis treatment. Generally speaking, the blood pump part often has a speed detection function to monitor the blood flow of the patient, and the blood flow is related to the removal of various toxins. Therefore, the setting of the distance between the blood pump runner and the groove must be accurate, and It needs to be adjusted frequently. According to the condition of the blood pump tube, the spacing is generally set to 3.2-3.3mm. It should not be too loose, otherwise it will cause inaccurate blood flow detection; it should not be too tight. If it is too tight, it will cause the pipeline to rupture and cause an accident. .
b. Heparin Pump (Heparin Pump): Heparin pump is equivalent to a microinjection pump used in clinical practice to continuously inject heparin into the patient's blood. Since the patient's blood is in contact with the air in the extracorporeal circulation, it is prone to coagulation. Use a heparin pump to prevent coagulation.
C. Arteriovenous pressure monitoring : Arterial pressure monitoring is used to monitor thrombosis, coagulation and pressure changes in the dialyzer. When blood flow is insufficient, arterial pressure will decrease; when there is coagulation and thrombosis in the dialyzer, arterial pressure will increase; venous pressure monitoring is used to monitor the pressure of blood return in the pipeline. When the dialyzer clots or thrombosis, the blood flow is insufficient, and the venous blood return needle falls off, the venous pressure will drop; if the blood return line is twisted and blocked or the return needle is blocked, the venous pressure will increase. When the above situation occurs, the machine will automatically alarm.
d. Air Detector: is used to monitor the blood flow path and the air bubbles in the IV drip pot. Generally, the principle of ultrasonic detection is used to avoid air embolism in patients. When air bubbles are detected, the detection system will drive the arterial and venous blood circuit clamp to block the blood flow and prevent the occurrence of danger.
(2). Dialysate supply system part
a. Temperature control system
It includes two parts: heating and temperature detection. In normal dialysis, the reverse osmosis water that meets the treatment standards is generally heated to 36-40°C, mixed with the concentrated solution, and the temperature sensor is used to detect the temperature, and then the heating is controlled to make the dialysate temperature and the setting The set temperature is consistent. Generally, the dialysate temperature is controlled at about 37°C, which can be adjusted appropriately according to the patient's condition. For machines with thermal disinfection, the heating temperature can reach 100°C during thermal disinfection.
b. Dosing system
Prepare qualified dialysate. Take carbonate dialysis as an example. The mixing ratio is: A liquid: B liquid: pure water = 1: 1.8334. At present, many machines use ceramic pumps for proportioning, and the preparation can be achieved by adjusting the speed of rotation. The accuracy of the dialysate.
c. Degassing system
There is a certain amount of air in water and concentrated solution. During the preparation of dialysate, gas will also be generated due to the presence of carbonate. These bubbles may cause blood air embolism in the dialysate, reduce the removal rate of waste, and affect dialysis. The flow and pressure of the fluid, which in turn affect the conductivity and concentration, requires the removal of air in the dialysate. The principle of negative pressure is used when degassing. Generally, the degassing pressure is set to about -600mmHg, but the negative pressure should be appropriately reduced in plateau areas.
d. Conductivity monitoring system
Generally, hemodialysis machines with carbonate dialysis function are often equipped with 2-3 conductivity monitoring modules. First, the concentration of A liquid is detected. If the concentration of A liquid reaches the requirement, then B liquid is sucked, and then the detected conductivity is the dialysate. Actual conductivity. The conductivity value monitored by the conductivity monitoring module is transmitted to the CPU circuit and compared with the set conductivity, and then the concentrated solution preparation system is controlled to make it prepare the dialysate that meets the requirements. The range of cation concentration in dialysate is usually 13.0-15.0ms/cm, and the concentration of dialysate is maintained between 13.8-14.2.
e. Ultrafitration monitoring system
Transmembrane pressure (Trans-membranous Press, TMP) pressure control or volume control is used to achieve the purpose of ultrafiltration and removal of water in the blood. As the transmembrane pressure increases, the corresponding ultrafiltration capacity will also increase when the time is determined. Since most of the hemodialysis patients have kidney failure or complete loss, unable to remove body water, so the ultrafiltration system is very important in hemodialysis machines.
f. Blood Leakage System
During the hemodialysis process, the membrane of the dialyzer may sometimes be broken, and blood leakage will occur at this time. In order to detect the occurrence of blood leakage, the general hemodialysis machine uses optical principles to detect hemoglobin in the dialysate, and its detection sensitivity is 0.25-0.35 ml hemoglobin/1 liter of dialysate, if there is precipitation or excessive dirt during the dialysis process, false alarms are prone to occur, which requires the operator to promptly remove the stolen goods at the blood leakage detection site.
