What is Hemodialysis?

Hemodialysis (HD) is one of the renal replacement treatments for patients with acute and chronic renal failure. It drains blood from the body to the outside, passes through a dialyzer composed of numerous hollow fibers, and the blood contains electrolyte solution (dialysate) with a similar concentration in the body inside and outside the hollow fibers, through dispersion, ultrafiltration, and adsorption It exchanges materials with the principle of convection, removes metabolic waste from the body, maintains electrolytes and acid-base balance; at the same time removes excess water from the body, and calls the entire process of purified blood return to hemodialysis.

Basic Information

Chinese name

Hemodialysis

Foreign name

HD

Indication

Hypercalcemia, hypocalcemia, hyperphosphatemia, etc.

Contraindications

Intracranial hemorrhage or elevated intracranial pressure, etc.

Equipment

Hemodialysis machine, water treatment system, dialysate

Principle of hemodialysis

1. Solute transport (1) Dispersion: It is the main mechanism of solute removal during HD. Solutes are transported from a high concentration side to a low concentration side by a concentration gradient. This phenomenon is called dispersion. The energy of the solute diffusion transport comes from the irregular movement of the molecules of the solute or the particles themselves (Brownian motion).
(2) Convection: The solute moves with the solvent through the semi-permeable membrane, which is called convection. . Not affected by the solute molecular weight and its concentration gradient difference, the dynamic force across the membrane is the hydrostatic pressure difference across the membrane, the so-called solute traction effect.
(3) Adsorption: It is the selective adsorption of certain proteins, poisons and drugs (such as 2-microglobulin, complement, inflammatory mediators, Endotoxin, etc.). The surface of all dialysis membranes is negatively charged, and the amount of negatively charged membranes determines the amount of heterogeneously charged proteins adsorbed. In the process of hemodialysis, some abnormally increased proteins, poisons and drugs in the blood are selectively adsorbed on the surface of the dialysis membrane, so that these pathogenic substances are removed, thereby achieving the purpose of treatment.
2. Water transfer (1) Definition of ultrafiltration: The movement of liquid through a semi-permeable membrane under the effect of hydrostatic pressure gradient or osmotic pressure gradient is called ultrafiltration. During dialysis, ultrafiltration refers to the movement of water from the blood side to the dialysate side. Conversely, if the water moves from the dialysate side to the blood side, it is called anti-ultrafiltration.
(2) Factors affecting ultrafiltration: gradient of purified water pressure; osmotic pressure gradient; transmembrane pressure; ultrafiltration coefficient.

Indications for hemodialysis

1. Acute kidney injury.
2. Acute heart failure caused by excessive volume load or hypertension that is difficult to control with drugs.
3. Severe metabolic acidosis and hyperkalemia that is difficult to correct.
4. Hypercalcemia, hypocalcemia and hyperphosphatemia.
5. Chronic renal failure with anemia that is difficult to correct.
6. Uremia neuropathy and encephalopathy.
7. Uremic pleurisy or pericarditis.
8. Chronic renal failure with severe malnutrition.
9. Unexplained organ dysfunction or decreased general condition.
10. Drug or poisoning.

Contraindications for hemodialysis

1. Intracranial hemorrhage or elevated intracranial pressure.
2. Severe shock that is difficult to correct with medication.
3. Severe myocardial disease with refractory heart failure.
4. Associated with mental disorders can not cooperate with hemodialysis treatment.

Hemodialysis equipment

The hemodialysis equipment includes a hemodialysis machine, a water treatment and a dialyzer, and a hemodialysis system.
1. Hemodialysis machine is the most widely used treatment instrument in blood purification treatment. It is a relatively complicated electromechanical integrated device. It consists of a dialysate supply monitoring device and an extracorporeal circulation monitoring device.
2. Water treatment system Because the patient's blood is exposed to a large amount of dialysate (120L) through the dialysis membrane during a dialysis, the city tap water contains various trace elements, especially heavy metal elements, and also contains some disinfectants, endotoxins and bacteria. Blood contact will cause these substances to enter the body. Therefore, 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 dilution water for condensed dialysate, and the device that performs a series of treatments on tap water is a water treatment system.
3. Dialyzer, also called "artificial kidney", consists of hollow fibers made of chemical materials, and numerous hollow holes are distributed on each hollow fiber. During dialysis, the blood passes through the hollow fibers and the dialysate flows backward through the hollow fibers. The solutes and water of some small molecules in the hemodialysis solution are exchanged through the holes in the hollow fibers. The final result of the exchange is in the blood. Uremic toxins and some electrolytes and excess water are removed into the dialysate and some bicarbonate and electrolytes in the dialysate enter the blood. In order to achieve the purpose of removing toxins, moisture, maintaining acid-base balance and stable internal environment. The total area of the entire hollow fiber, that is, the exchange area, determines the passing capacity of small molecular substances, and the size of the membrane pore size determines the passing capacity of medium and large molecules.
4. Dialysate The dialysate is obtained by diluting the dialysis concentrate containing electrolytes and bases with reverse osmosis water in proportion, and finally forms a solution close to the blood electrolyte concentration to maintain normal electrolyte levels, while providing it with a higher base concentration The base is given to the body to correct the acidosis present in the patient. The commonly used dialysate bases are mainly bicarbonate and also contain a small amount of acetic acid.