How Does a Dialysis Machine Work

How Does a Dialysis Machine Work?By Joe S., DaVita Bio-medical TechnicianDialysis patients are all too familiar with the routine of their treatments: Go to the clinic, get weighed, have their temperature and blood pressure taken, get stuck with needles (unless the patient has a catheter access), have tubes connected from their access to the dialyzer and then sit in the chair until it is time to go home. While waiting, have you ever wondered how a dialysis machine works?As “the machine man,” I would like to take this opportunity to explain how your dialysis machine works by answering some of t he most frequently asked questions.What does my dialysis machine do?The dialysis machine mixes and monitors the dialysate. Dialysate is the fluid that helps remove the unwanted waste products from your blood. It also helps get your electrolytes and minerals to their proper levels in your body. The machine also monitors the flow of your blood while it is outside of your body. You may hear an alarm go off from time to time. This is how the machine lets us know that something needs to be checked.What are those plastic jugs sitting in front of my machine?The plastic jugs hold the liquids used to mix the dialysate. The machine mixes the dialysate, which is made up of an acidified solution, bicarbonate and purified water. The acidified solution contains electrolytes and minerals. You may hear it referred to as “acid.” The other solution is bicarbonate or bicarb, which is like baking soda. Both are mixed inside the machine with purified water. While you are dialyzing, dialysate and your blood flow through the dialyzer (but they never touch). Fresh dialysate from the machine enters your dialyzer throughout your treatment. Impurities are filtered out of your blood into the dialysate. Dialysate containing unwanted waste products and excess electrolytes leave the dialyzer and are washed down the drain.How does my blood get in and out of my body?Blood tubing carries your blood from your access to the dialyzer. The blood tubing is threaded through the blood pump. You’ll see t he blood pump turning in a circular motion. The pumping action of the blood pump pushes your blood through the dialyzer and back into your body.What’s in the syringe that’s attached to my machine?Blood tends to clot when it moves through the blood tubing. To prevent this the nurse will give you a drug called “heparin.” Your doctor orders the amount of heparin you get at each treatment. That amount of heparin is drawn up into a syringe then placed on the machine into the “heparin pump.” The heparin pump is programmed to release the right amount of heparin into your blood tubing during your treatment. The heparin prevents your blood from clotting.How does the machine keep me safe?One problem that may occur during dialysis is that air gets into the blood tubing. To prevent this from happening, blood tubings have two air traps built into them. One trap is before the dialyzer and the other is after it. These traps catch any air that may get into the system. If air does get past these traps an internal machine air sensor shuts down the blood pump and an alarm will sound. All blood flow is stopped until the air is removed.Why are there so many alarms?The machine continuously monitors the pressures created by your blood inside the blood tubing and dialyzer. It also monitors the blood flow, temperature and proper mixture of the dialysate. If any of these go out of range, the machine lets us know by sounding an alarm, blinking lights and shutting down blood or dialysate flow. It also lets us know if your blood pressure is too low or high. Oh yes, it also alarms when it’s time to go home.Want to know more?I realize that this may not answer all of your questions. That’s why I invite you to ask the bio-medical technician (machine person) at your dialysis center any questions you have. Your bio-medical technician will be happy to share any information with you. The more you know, the more comfortable you will be with your treatments.What Is Hemodialysis?While healthy kidneys have several functions in the body, the most well-known job is to produce urine. When kidney function goes below 10% to 15% 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. Fortunately, we live in a time when there are treatments and medicines that can replace the functions of the kidneys and keep the body alive. One type of renal replacement therapy — meaning a treatment that replaces kidney function — is hemodialysis. Hemodialysis is a therapy that filters waste, removes extra fluid and balances electrolytes (sodium, potassium, bicarbonate, chloride, calcium, magnesium and phosphate).How is hemodialysis done?In hemodialysis, blood is removed from the body and filtered through a man-made membrane called a dialyzer, or artificial kidney, and then the filtered blood is returned to the body. The average person has about 10 to 12 pints of blood; during dialysis only one pint (about two cups) is outside of the body at a time. To perform hemodialysis there needs to be an access 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 vascular 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 has to have removed during the treatment. The patient is then “put on the machine”. Patien t 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, the other needle puts it back. Patients with a central venous catheter will have the two tubes from their access connected to the blood tubes that lead to the dialyzer and back to the body. Once the patient is “put on the machine”, the dialysis machine is programmed and t hen 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 blood tubes that carry the blood from the body to thedialyzer and back to the body. The dialysis machine also has many safety detection features. If you visit a dialysis center, you will likely hear some of the warning sounds made by a dialysis machine.How does hemodialysis work?The dialyzer is the key to hemodialysis. The dialyzer is called the artificial kidney because it filters the blood — a job the kidneys used to do. 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 one 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 toge ther. 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 does not allow blood cells to pass through.Dialysate, also called dialysis fluid, dialysis solution or 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. The way this works is through a process called diffusion. In the blood of the hemodialysis patient, there is a high concentration of waste, while 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. The 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.How often is hemodialysis done?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 about four hours each session. Your doctor will prescribe how long your treatments will be, usually between 3 to 5 hours, but most common is 4 hours. Talk to your doctor about how long you should be on hemodialysis. Some people feel that dialysis lasts a long time; however, 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 schedules include nocturnal and short daily. Normally, these treatments are performed by people who do 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 “washed out” feeling reported after traditio nal hemodialysis. More dialysis centers are beginning to offer in-center nocturnal hemodialysis based on reports of patients feeling better about their quality of life and having good lab results. Short daily hemodialysis is performed five or six times per week for about two to three hours each treatment. Talk to your doctor if you are interested in home hemodialysis (HHD) or in-center nocturnal dialysis. You may want to ask your social worker if addition treatments, such as the longer nocturnal hemodialysis and short daily hemodialysis will be covered through your insurance.Advantages and disadvantages of hemodialysisHemodialysis is an effective treatment for those with end stage renal disease. However, hemodialysis alone will not provide a complete treatment for those with kidney failure. Diet and fluid restrictions need to be followed, and medicines may need to be taken to replace other functions of the kidneys, such as regulating blood pressure and stimulating production of red blood cells to prevent anemia.For those who choose in-center hemodialysis, some of the benefits are that they will have their treatments performed in a dialysis center by trained professionals. They can spend their time in dialysis sleeping, reading, writing, watching television, listening to music or doing other quiet activities. There are four days a week when they will not have to go to dialysis. Some of the disadvantages are that they will have to travel to and from hemodialysis three times each week and it takes advanced notice to travel and arrange for dialysis in a visiting dialysis center. The diet restrictions include limiting foods that contain phosphorus, potassium and sodium and drinking a limited amount of fluid. Some peo ple report a “washed out” feeling after hemodialysis and go home to take a nap. Those who perform nocturnal hemodialysis (in center or at home) report that this washed out feeling is not as common. Also, because nocturnal dialysis is performedduring nonpr oductive sleeping hours, many people report they feel that their lives are more “normal” because they don’t have to take time out of their days for dialysis.People who choose to perform hemodialysis at home say they enjoy the feeling of control they have over their lives. Instead of going to the dialysis center at a certain time, they can choose when to perform hemodialysis around their schedule.There is another type of dialysis called peritoneal dialysis (PD). PD is done by filling the peritoneum in the abdomen with dialysate and using the peritoneal membrane as a semipermeable membrane. There are diet and fluid restrictions with peritoneal dialysis; however, these are usually not as limited as hemodialysis because this therapy is performed every day. PD treatments are performed at home, and so do not require three visits to a treatment center each week. Peritoneal dialysis also has a nighttime treatment option that makes it easier for patients to work, attend school or travel.All dialysis treatments have their advantages and disadvantages. Based on your lifestyle and medical needs, you and your doctor can discuss your options and decide which one is right for you.。