Principle:
1. Solute transport
(1) Diffusion: It is the main mechanism of solute removal during HD. The solute is transported from the high-concentration side to the low-concentration side by means of a concentration gradient, a phenomenon called dispersion. The energy of solute diffusion transport comes from the irregular motion (Brownian motion) of the molecules or particles of the solute itself.
(2) Convection: The movement of the solute through the semipermeable membrane along with the solvent is called convection. Not affected by the molecular weight of the solute and its concentration gradient difference, the driving force across the membrane is the hydrostatic pressure difference on both sides of the membrane, which is the so-called solute pulling effect.
(3) Adsorption: It is the selective adsorption of certain proteins, poisons and drugs (such as β2-microglobulin, complement, inflammatory mediators, endotoxin, etc.). The surface of all dialysis membranes is negatively charged, and the amount of negative charge on the membrane surface determines the amount of adsorbed proteins with foreign charges. In the process of hemodialysis, some abnormally elevated proteins, poisons and drugs in the blood are selectively adsorbed on the surface of the dialysis membrane, so that these pathogenic substances are removed, so as to achieve the purpose of treatment.
2. Water transport
(1) Ultrafiltration definition: The movement of liquid through a semipermeable membrane under the action of a hydrostatic pressure gradient or an osmotic pressure gradient is called ultrafiltration. During dialysis, ultrafiltration refers to the movement of water from the blood side to the dialysate side; on the contrary, if the water moves from the dialysate side to the blood side, it is called reverse ultrafiltration.
(2) Factors affecting ultrafiltration: ① water pressure gradient; ② osmotic pressure gradient; ③ transmembrane pressure; ④ ultrafiltration coefficient.
Indications
1. Acute kidney injury.
2. Acute heart failure caused by volume overload or hypertension that is difficult to control with drugs.
3. Severe metabolic acidosis and hyperkalemia that is not easy to correct.
4. Hypercalcemia, hypocalcemia and hyperphosphatemia.
5. Chronic renal failure combined with anemia that is difficult to correct.
6. Uremic neuropathy and encephalopathy.
7. Uremic pleurisy or pericarditis.
8. Chronic renal failure combined with severe malnutrition.
9. Unexplained organ dysfunction or general decline.
10. Drug or poison poisoning
Hemodialysis equipment
Hemodialysis equipment includes hemodialysis machine, water treatment and dialyzer, which together form a hemodialysis system.
1. Hemodialysis machine
It is the most widely used therapeutic instrument in blood purification treatment. It is a relatively complex electromechanical integration device, which consists of a dialysate supply monitoring device and an extracorporeal circulation monitoring device.
2. Water treatment system
Since the patient's blood is in contact with a large amount of dialysate (120L) through the dialysis membrane in one dialysis, and urban tap water contains various trace elements, especially heavy metal elements, as well as some disinfectants, endotoxins and bacteria, contact with blood will cause these substances into the body. Therefore, the tap water needs to be filtered, iron removed, softened, activated carbon, and reverse osmosis treatment in sequence. Only reverse osmosis water can be used as the dilution water for concentrated dialysate, and the device that performs a series of treatment on tap water is the water treatment system.
3. Dialyzer
Also known as "artificial kidney", it consists of hollow fibers made of chemical materials, and each hollow fiber is distributed with numerous small holes. During dialysis, the blood passes through the hollow fibers and the dialysate flows backward through the hollow fibers. Some small molecules of solutes and water in the hemodialysate are exchanged through the holes on the hollow fibers. The final result of the exchange is blood in the blood. Uremic toxins, some electrolytes, and excess water enter the dialysate to be removed, and some bicarbonate and electrolytes in the dialysate enter the blood. So as to achieve the purpose of removing toxins, water, maintaining acid-base balance and stable internal environment. The total area of the entire hollow fiber, that is, the exchange area, determines the passage capacity of small molecules, while the size of the membrane pore size determines the passage capacity of medium and large molecules.
4. Dialysate
The dialysate is obtained by proportionally diluting the dialysis concentrate containing electrolytes and bases with reverse osmosis water, and finally forms a solution with a concentration close to blood electrolytes to maintain normal electrolyte levels, while providing bases to the body through a higher base concentration. , to correct the patient's existing acidosis. The commonly used dialysate bases are mainly bicarbonate and also contain a small amount of acetic acid.
