Hemodialysis

Hemodialysis is one of the renal replacement treatments for patients with acute and chronic renal failure. It drains blood from the body to the outside of the body and passes through a dialyzer composed of countless hollow fibers. The blood and the electrolyte solution (dialysis fluid) with similar concentrations of the body are in and out of the hollow fibers through diffusion, ultrafiltration, and adsorption. It exchanges substances with the principle of convection, removes metabolic wastes in the body, maintains electrolyte and acid-base balance; at the same time, removes excess water in the body, and the entire process of returning purified blood is called hemodialysis.

principle

1. Solute transport
(1) Dispersion: It is the main mechanism of solute removal in HD. The solute is transported from the high-concentration side to the low-concentration side depending on the concentration gradient. This phenomenon is called dispersion. The dispersive transport energy of solute comes from the irregular movement of solute molecules or particles themselves (Brownian motion).
(2) Convection: The movement of solutes through the semipermeable membrane along with the solvent is called convection. Unaffected by the solute molecular weight and its concentration gradient difference, the power across the membrane is the hydrostatic pressure difference on both sides of the membrane, which is the so-called solute traction.
(3) Adsorption: It is through the interaction of positive and negative charges or van der Waals forces and hydrophilic groups on the surface of the dialysis membrane to selectively adsorb 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 heterogeneous charges. In the process of hemodialysis, certain 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 transfer
(1) Ultrafiltration definition: The movement of liquid through a semi-permeable 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; conversely, if the water moves from the dialysate side to the blood side, it is called reverse ultrafiltration.
(2) Factors affecting ultrafiltration: ①purified water pressure gradient; ②osmotic pressure gradient; ③transmembrane pressure; ④ultrafiltration 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 difficult to correct.
4. Hypercalcemia, hypocalcemia and hyperphosphatemia.
5. Chronic renal failure with anemia that is difficult to correct.
6. Uremic neuropathy and encephalopathy.
7. Uremia pleurisy or pericarditis.
8. Chronic renal failure combined with severe malnutrition.
9. Unexplainable organ dysfunction or decline in general condition.
10. Drug or poison poisoning.

Contraindications

1. Intracranial hemorrhage or increased intracranial pressure.
2. Severe shock that is difficult to correct with drugs.
3. Severe cardiomyopathy accompanied with refractory heart failure.
4. Accompanied by mental disorders cannot cooperate with hemodialysis treatment.

Hemodialysis equipment

The equipment of hemodialysis includes hemodialysis machine, water treatment and dialyzer, which together form the hemodialysis system.
1. Hemodialysis machine
is one of the most widely used therapeutic equipment in blood purification treatment. It is a relatively complex mechatronics equipment, composed of dialysate supply monitoring device and extracorporeal circulation monitoring device.
2. Water treatment system
Since the patient’s blood in a dialysis session has to contact a large amount of dialysate (120L) through the dialysis membrane, and urban tap water contains various trace elements, especially heavy metals, as well as some disinfectants, endotoxins and bacteria, contact with blood will cause these The substance enters the body. Therefore, the tap water needs to be filtered, iron removed, softened, activated carbon, and reverse osmosis processed in sequence. Only reverse osmosis water can be used as the dilution water for the concentrated dialysate, and the device for a series of treatments of the tap water is the water treatment system.
3. Dialyzer
is also called “artificial kidney”. It is composed of hollow fibers made of chemical materials, and each hollow fiber is distributed with numerous small holes. During dialysis, the blood flows through the hollow fiber and the dialysate flows backward through the hollow fiber. The solute and water of some small molecules in the hemodialysis fluid are exchanged through the small holes on the hollow fiber. The final result of the exchange is the blood in the blood. Uremia toxins, some electrolytes, and excess water are removed in the dialysate, 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 internal environment stability. The total area of ​​the entire hollow fiber, the exchange area, determines the passage capacity of small molecules, and the size of the membrane pore size determines the passage capacity of medium and large molecules.
4. Dialysate
The dialysate is obtained by diluting the dialysis concentrate containing electrolytes and bases and reverse osmosis water in proportion, and finally forms a solution close to the blood electrolyte concentration to maintain normal electrolyte levels, while providing bases to the body through a higher base concentration , To correct the acidosis in the patient. Commonly used dialysate bases are mainly bicarbonate, but also contain a small amount of acetic acid.