Dialysis cleans blood through a membrane, and your own belly lining can serve as one
When kidneys fail, a machine can take over part of their job, pumping blood through thousands of hair-thin hollow fibres that let waste out and keep blood cells in. There is another way too: the lining of the abdomen itself can act as the filter, letting some patients clean their blood at home.
Healthy kidneys balance water and minerals such as sodium, potassium and calcium, flush out acidic waste, and make hormones that drive red blood cell production and bone formation. Dialysis copies only the cleaning part. It relies on diffusion, the drift of dissolved substances from high concentration to low, and on ultrafiltration, which pushes out excess fluid. Blood flows on one side of a semipermeable membrane and a prepared fluid called dialysate on the other; small molecules cross, while red cells and large proteins stay put. The first successful treatment took place in 1943.
In haemodialysis, blood leaves the body and passes through a dialyser packed with synthetic fibres while dialysate flows the opposite way, a counter-current that keeps the concentration gradient steep so more urea and creatinine escape. The fluid's potassium and calcium match healthy blood, and its bicarbonate is set slightly higher to counter the acidity common in kidney failure. A typical four-hour session can remove several litres of fluid. In the United States sessions are usually held three times a week at a centre, partly because of Medicare rules, though studies show longer, more frequent sessions, often overnight at home, work better.
Peritoneal dialysis happens inside the body. A sterile glucose solution is run into the abdominal cavity, and the peritoneum, the membrane around the intestines, does the filtering. Patients repeat the exchange four or five times a day, or let a machine cycle overnight. It is less efficient per hour than haemodialysis but runs longer, so overall waste removal is similar, and it needs little more than bags of fresh fluid.
Dialysis is started when kidney function collapses suddenly, or when chronic failure reaches stage 5, with filtration below 15 percent of normal. It can bridge the wait for a transplant or serve as permanent treatment.
Source: Kidney dialysis
