1. The principle of hemodialysis
Dialysis refers to the process of solutes passing through the membrane from one side of the semi-permeable membrane to the other. Any natural (such as peritoneum) or artificial semi-permeable membrane, as long as the membrane contains pores that allow a certain size of solute to pass through, then these The solute can then move from one side of the membrane to the other side of the membrane by diffusion and convection. "Poisons" in the human body include metabolites, drugs, and exogenous poisons. As long as their atomic weight or molecular weight is appropriate, they can be removed from the body through dialysis. The basic principle is dispersion and convection. Dispersion is the concentration gradient of the solute contained in the liquid on both sides of the semipermeable membrane and the different osmotic concentration formed by it. The solute moves from the side with high concentration to the side with low concentration through the semipermeable membrane. Convection, also known as ultrafiltration, refers to the process in which solutes and solvents are transported across the membrane due to the difference in hydrostatic pressure and osmotic pressure gradient on both sides of the dialysis membrane. Hemodialysis can excrete excess water and metabolic waste from the patient's body, and absorb electrolytes and bases lacking in the body from the dialysate to achieve the purpose of correcting the balance of water, electrolyte and acid-base.
Second, the progress of the dialysis process
At the beginning of dialysis, the patient's blood is introduced into the arterial tube through the vascular access, the defoamer, and reaches the analyzer. The blood and dialysate are exchanged countercurrently with the help of the semipermeable membrane in the dialyzer. The exchanged dialysate enters the waste tank and is discarded, while the "purified" blood is re-injected from the venous vascular access through the defoamer and the venous pipeline. The patient's body, in order to achieve the purpose of "cleaning".
Three, the basic components of hemodialysis fluid
The basic components of hemodialysis fluid are:
(1) Sodium: Sodium is the main cation in the extracellular fluid, which plays an important role in maintaining plasma osmotic pressure and blood volume. In order to maintain the balance of sodium in dialysis patients, the sodium in the dialysate needs to be slightly lower than the normal serum sodium value, and the concentration is generally 130-140mmol/L.
(2) Potassium: Potassium is the main cation in the intracellular fluid. The potassium concentration of the dialysate is generally 0~4mmol/L. The dialysate with different potassium concentrations can be selected according to different needs. Potassium-free dialysate (0～1mmol/L), mainly used for ARF anuric or high catabolism patients or the first 1-2 hours of hyperkalemia initiation of dialysis; low potassium dialysate (2mmo l/L), mostly used Patients with high blood potassium before each dialysis or high blood potassium during the induction period; conventional dialysate (3 ~ 4mmol/L), used for maintenance dialysis with normal potassium before dialysis or patients taking digitalis.
(3) Calcium: The blood calcium level of maintenance hemodialysis patients is mostly low, and the blood calcium reaches normal or mildly positive balance during dialysis. The calcium content of the dialysate should be between 1.5 and 1.75 mmol/L.
(4) Magnesium: CRF often has hypermagnesemia, and the magnesium concentration of dialysate is generally 0.6-1mmol/L, which is slightly lower than normal plasma magnesium.
(5) Chlorine: The chloride ion in the dialysate is basically the same as the extracellular fluid, which is determined by the concentration of cations and sodium acetate, and the concentration is 96-110mmol/L.
(6) Alkaline agents: CRF patients have varying degrees of metabolic acidosis and increased anion gap. The buffering bicarbonate (HCO3-) is reduced, and it needs to be supplemented from the dialysate, acetate and bicarbonate. Salt can produce HCO3- and can be used to supplement the lack of HCO3- in the body. The usual concentration of acetate is 35-40mmol/L, and the concentration of bicarbonate is generally 32-38mmol/L;
(7) Glucose: Choose dialysate with different sugar concentration according to needs, divided into three types: sugar-free dialysate, high-sugar dialysate (10-20g/L), and low-sugar dialysate (1-2g/L)
