While healthy kidneys have several functions in the body, their most well-known job is to produce urine. When kidney function drops below 10 to 15 percent, kidneys are no longer able to filter the blood and make urine. This causes toxins to build up in the body, along with excess fluid. Hemodialysis is a treatment for this.
In hemodialysis, blood is removed from the body and filtered through a manmade membrane called a dialyzer or artificial kidney, and then the filtered blood is returned to the body. The average person has 10 to 12 pints of blood; during dialysis only one pint (about two cups) at a time is outside of the body. To perform hemodialysis an access must be created to get the blood from the body to the dialyzer and back to the body. There are three access types for hemodialysis: arteriovenous (AV) fistula, AV graft and central venous catheter. The AV fistula is the access most recommended by the dialysis community; however, you and your doctor will decide which access is best for you.
When a patient goes to hemodialysis, a nurse or technician will check vital signs and get the patient’s weight. The weight gain will tell how much excess fluid the patient must have removed during the treatment. The patient is then“put on the machine." A patient with a vascular access (AV fistula or AV graft) will get two needle sticks in their access; one needle takes blood out of the body, and the other needle puts it back. Patients with a central venous catheter will have two tubes from their access connected to tubes that lead to the dialyzer and back to the body. The dialysis machine is programmed and then treatment begins.
Blood never actually goes through the dialysis machine. The dialysis machine is like a big computer and a pump. It keeps track of blood flow, blood pressure, how much fluid is removed and other vital information. It mixes the dialysate, or dialysis solution, which is the fluid bath that goes into the dialyzer. This fluid helps pull toxins from the blood, and then the bath goes down the drain. The dialysis machine has a blood pump that keeps the blood flowing by creating a pumping action on the tubes that carry the blood from the body to the dialyzer and back to the body. The dialysis machine also has many safety features to assist nurses in caring for patients.
The dialyzer is the key to hemodialysis. The dialyzer is called the artificial kidney because it filters the blood—a job that healthy kidneys do themselves. The dialyzer is a hollow plastic tube about a foot long and three inches in diameter that contains many tiny filters. (Dialyzers are made in different sizes so doctors can prescribe the best ones for their patients.)
There are two sections in the dialyzer: the section for dialysate and the section for the blood. The two sections are divided by a semipermeable membrane so that they don’t mix together. A semipermeable membrane has microscopic holes that allow only some substances to cross the membrane. Because it is semipermeable, the membrane allows water and waste to pass through, but prevents blood cells from passing through.
Dialysate, also called dialysis fluid, dialysis solution or dialysate bath, is a solution of pure water, electrolytes and salts, such as bicarbonate and sodium. The purpose of dialysate is to pull toxins from the blood into the dialysate. This works through a process called diffusion.
In the blood of the hemodialysis patient, there is a high concentration of waste, and the dialysate has a low concentration of waste. Due to the difference in concentration, the waste will move through the semipermeable membrane to create an equal amount on both sides. The dialysis solution is then flushed down the drain along with the waste. The electrolytes in the dialysis solution are also used to balance the electrolytes in the patient's blood. Extra fluid is removed through a process called filtration. The fluid is pushed off by higher pressure on the blood side than on the dialysate side.
Blood needs to flow through the dialyzer for several hours to adequately clean the blood and rid the body of excess fluid. Traditional, in-center hemodialysis is generally done three times a week for 3 to 5 hours per session. Your doctor will prescribe how long your treatments will be, but most common is 4 hours. Talk to your doctor about how long you should be on hemodialysis. Healthy kidneys work 24 hours a day, 7 days a week and dialysis must do the job in only 12 or so hours a week.
Alternative hemodialysis options that may be available internationally but are not yet readily available in Taiwan include nocturnal and short daily hemodialysis sessions. Normally, these treatments are performed by people who are already doing home hemodialysis.
With nocturnal hemodialysis, the patient has dialysis for about eight hours overnight while sleeping. This is a longer, gentler treatment, so patients say they have fewer problems with cramping and the wiped-out feeling reported after traditional hemodialysis.
Alternative and supplemental treatment modalities, such as hemofiltration and hemoperfusion, may be available in Taiwan. Talk to your doctor to see if these are beneficial to you.
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