Dialysis is a treatment that performs some of the functions of failing kidneys. A key element of this process is a specialized fluid called dialysate, which removes waste products and excess fluid from the blood. The dialysis machine mixes and monitors the dialysate, composed of purified water, electrolytes, and minerals. Fresh dialysate flows through a filter, called a dialyzer, during treatment as the used solution is drained away.
The Role of Dialysate in Dialysis
Dialysate’s function is to clean the blood by removing metabolic waste and balancing electrolyte and fluid levels through diffusion and osmosis. During dialysis, blood flows on one side of a semipermeable membrane within a dialyzer, while dialysate flows on the opposite side. The membrane’s pores allow waste and water to pass through but block larger components like proteins and blood cells.
Waste products like urea and creatinine are highly concentrated in the blood of those with kidney failure, while the dialysate is formulated with a very low concentration of these substances. This difference in concentration, known as a gradient, drives waste from the blood into the dialysate. Excess water is removed from the blood through osmosis, where water moves toward an area with a higher solute concentration, which can be created by adding sugar to the dialysate.
Composition of Dialysate
The effectiveness of dialysis depends on the precise composition of the dialysate, a prepared mixture of several components. This fluid is not a uniform solution but is formulated to meet a patient’s specific blood chemistry. The base is highly purified water, combined with electrolytes and a buffer.
Purified Water
The water used for dialysate is not ordinary tap water; it undergoes extensive purification to remove minerals, chemicals, and bacterial contaminants. This prevents harmful substances from entering the patient’s bloodstream. The dialysis machine handles the final mixing of this water with concentrated solutions before treatment.
Electrolytes
Electrolytes are minerals that healthy kidneys keep in balance. Dialysate contains a specific mix of electrolytes, including sodium, potassium, calcium, and magnesium, at levels that are considered normal for healthy blood. The concentration of these minerals helps correct imbalances in the patient’s blood. For instance, if a patient has high potassium levels, the dialysate will have a lower potassium concentration to encourage the excess to diffuse out of the blood.
A Buffer
Kidney failure can lead to metabolic acidosis, where the blood becomes too acidic. To counteract this, a buffer like bicarbonate is added to the dialysate. The buffer moves from the dialysate into the blood, helping to neutralize the excess acid and restore the blood’s proper pH balance.
Glucose (Dextrose)
Glucose, as dextrose, is another component with a prominent role in peritoneal dialysis. In this treatment, the dialysate is instilled into the abdominal cavity, where dextrose creates a strong osmotic gradient to pull excess fluid from blood vessels. In hemodialysis, glucose may be present in smaller amounts to prevent a patient’s blood sugar from dropping too low during the procedure.
How Dialysate is Customized
Dialysate is not a generic fluid; it is tailored to each individual’s physiological needs, similar to a medical prescription. A nephrologist determines the precise formulation based on regular analysis of the patient’s blood work. This customization ensures the treatment effectively corrects the unique imbalances present in the patient’s body.
The concentration of electrolytes is a frequently adjusted component. For example, a patient with low calcium levels might receive a dialysate with a higher calcium concentration to help replenish their body’s supply. This principle applies to all electrolytes to correct specific deficiencies or excesses.
The buffer concentration is also adjusted based on the severity of a patient’s metabolic acidosis. The glucose or dextrose concentration, especially in peritoneal dialysis, can be varied. Using a higher dextrose concentration will pull more fluid from the body, which is useful for patients who retain significant water between treatments.
Safety and Preparation
The safety and sterility of dialysate are important to prevent complications. Because dialysate comes into close contact with blood, any contamination can introduce harmful substances like bacteria and their byproducts, known as endotoxins. This can cause systemic infections and inflammatory responses.
To mitigate these risks, stringent quality control measures are in place. In hemodialysis centers, the dialysate is prepared on-site by a machine that mixes purified water with concentrated acid and bicarbonate solutions. The dialysis machine continuously monitors the temperature and conductivity of the final dialysate to ensure it is correctly mixed.
For peritoneal dialysis, the fluid must be completely sterile as it is introduced into the abdominal cavity. This type of dialysate comes in pre-packaged, sterile bags. Patients performing this treatment at home are trained in sterile techniques to connect and disconnect the bags. Regular testing of the water and dialysate solutions is standard in all dialysis settings.