Kidney dialysis

Kidney dialysis is a vital medical process used to clean the blood. It removes excess water, toxins, and solutes when the kidneys can no longer do this naturally. This treatment is a type of renal replacement therapy. It can be used as a temporary measure for acute kidney injury, which is a sudden loss of function. It is also used for chronic kidney failure, which is a gradual decline in function.

In stage 5 chronic kidney failure, the glomerular filtration rate drops below 15% of normal. At this stage, creatinine clearance is less than 10 mL per minute, and uremia is present. Dialysis helps keep the body in balance while patients wait for a kidney transplant or as a permanent solution.

To understand dialysis, we must look at how the kidneys work. Healthy kidneys maintain the body's internal equilibrium of water and minerals. They manage levels of sodium, potassium, chloride, calcium, phosphorus, magnesium, and sulphate. They also excrete acidic metabolism end-products that the body cannot remove through breathing. Furthermore, kidneys act as part of the endocrine system. They produce erythropoietin for red blood cell production and calcitriol for bone formation.

Because dialysis cannot replace these endocrine functions, it is considered an imperfect replacement for the organ.

Dialysis relies on two main physical principles: diffusion and ultrafiltration. Diffusion is the movement of substances from an area of high concentration to an area of low concentration. In dialysis, blood flows on one side of a semipermeable membrane. A special liquid called dialysate flows on the opposite side.

A semipermeable membrane is a material with tiny pores. These pores allow small solutes and fluids to pass through. However, the membrane blocks larger substances like red blood cells and large proteins. This process mimics how the kidney's glomerulus separates small substances from large ones.

Hemodialysis is the most common primary type of dialysis. In this method, blood is pumped outside the body through an external filter called a dialyzer. The dialyzer contains thousands of tiny, hollow synthetic fibers that act as the semipermeable membrane.

To make the process more efficient, the blood and dialysate move in opposite directions. This is called counter-current flow. It maximizes the concentration gradient to help remove urea and creatinine. The dialysate contains specific levels of minerals. For example, bicarbonate levels are set slightly higher than in normal blood to help neutralize metabolic acidosis. Ultrafiltration also occurs by applying negative pressure to the dialysate compartment. This pressure gradient pulls excess water and dissolved solutes from the blood into the dialysate.

Peritoneal dialysis is another primary method that happens inside the body. Instead of an external machine, it uses the peritoneum as a natural semipermeable membrane. The peritoneum is the lining of the abdominal cavity.

A sterile dialysate containing glucose is run through a tube into the peritoneal cavity. Wastes and water move from the blood, across the visceral peritoneum, and into the dialysate. This exchange is repeated four to five times per day. While it is less efficient than hemodialysis, the long duration of the treatment results in similar waste removal. Many patients perform this at home, which offers more flexibility than visiting a clinic.

There are also specialized methods like hemofiltration and hemodiafiltration. Hemofiltration is a primary treatment that uses a pressure gradient instead of dialysate. Water moves rapidly across a very permeable membrane, "dragging" large molecular weight substances along with it. Because this process removes salts and water, a substitution fluid must be infused into the circuit to replace them.

Hemodiafiltration combines the principles of both hemodialysis and hemofiltration. It is often used to purify blood from toxins or to treat acute kidney injury.

Medical history shows how far this technology has come. The first successful dialysis was performed in 1943. In the United States, hemodialysis is a very common hospital procedure. In 2011, it accounted for 909,000 hospital stays, which was a rate of 29 stays per 10,000 people. While many patients visit centers three times a week, some practice nocturnal daily hemodialysis at home. This involves longer, more frequent treatments while sleeping. Studies show these frequent treatments can improve the clearance of molecules and decrease the need for phosphate binders.