What is dialysate?
Dialysate is the liquid that needs to be used to exchange solutes with blood through diffusion on both sides of the dialysis membrane during hemodialysis. The dialysate contains K+, Na+, Ca2+, Mg2+, Cl-, HCO3- and acetic acid. The dialysate has a certain osmotic pressure and is used for rectal, peritoneal or extracorporeal dialysis.
Basic components of dialysate
1. Sodium
Sodium is the main cation in extracellular fluid and plays an important role in maintaining plasma osmotic pressure and blood volume. In order to maintain the sodium balance of dialysis patients, the sodium in the dialysate should be slightly lower than the normal serum sodium value, and the concentration is generally 135~145mmol/L.
2. Potassium
Potassium is the main cation in intracellular fluid, and the dialysate concentration is generally 0~4mmol/L, and dialysate with different potassium concentrations can be selected according to different needs. Potassium-free dialysate is mainly used for patients with acute renal failure in the anuric phase or high catabolism or in the first 1 to 2 hours of starting dialysis with hyperkalemia; low-potassium dialysate is mostly used for high serum potassium before each dialysis or induction phase Patients with hyperkalemia; routine dialysate for maintenance dialysis with normokalemia before dialysis or patients taking digitalis.
3. Calcium
The calcium concentration in the dialysate is extremely important to maintain the homeostasis of calcium in the body, and can avoid adverse reactions caused by the disorder of calcium metabolism in the patient. Most of the patients on maintenance hemodialysis have low blood calcium levels. In order to achieve normal or slightly positive balance of blood calcium during dialysis, the calcium content of the dialysate should be between 1.25 and 1.75 mmol/L.
4. Magnesium
Chronic renal failure often has hypermagnesemia, and the magnesium concentration in dialysate is generally 0.5-0.75mmol/L, which is slightly lower than normal plasma magnesium.
5. Chlorine
The chloride ion in the dialysate is basically the same as that in the extracellular fluid, which is determined by the concentration of cations and sodium acetate, and the concentration is 100~115mmol/L.
6. Base
Patients with chronic renal failure have varying degrees of metabolic acidosis and increased anion gap, and the buffering bicarbonate (HCO3-) decreases, which needs to be supplemented from the dialysate. Acetate and oxycarbonate can produce HCO3-, can be used to supplement the deficiency of HCO3- in the body. The common concentration of acetate is 35-40mmol/L, and the concentration of bicarbonate is generally 30-40mmol/L.
7. Glucose
Dialysates with different sugar concentrations are selected according to the needs, which are divided into three types: sugar-free dialysate, high-glucose dialysate and low-glucose dialysate.
Configuration of the dialysate
The dialysate is prepared and stored in the form of concentrated solution, and the concentration ratio is mostly about 35 times. HCO3- and Ca2+, Mg2+ are easy to form precipitation, so HCO3- is separated, prepared and stored separately in the form of concentrated sodium bicarbonate strong alkali solution, which is called B solution; the rest of the components are combined into strong acid concentrated solution, called A liquid.
Concentrated liquid B is formulated to avoid bacterial growth of bicarbonate concentrate and reduce transportation and storage prices. Solid sodium bicarbonate is often packed in plastic bags, sealed, and dissolved in pure water before use. Bicarbonate can also be put into a special tank, directly installed on the hemodialysis machine during dialysis, and the machine will automatically dissolve and dilute it while dialysis.
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