What Is Hemodialysis and How Does It Work?

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I take care of dialysis patients daily. Now, when I first meet a patient in the early stages of kidney disease, my primary goal is to reverse the kidney disease, or at least to prevent or slow down its progression. However, in the United States, over 30 million Americans have kidney disease, and sometimes, this kidney disease does progress to kidney failure or end-stage renal disease. When this happens, you cannot survive unless you have a kidney transplant or some form of dialysis. So today we're going to talk about hemodialysis. What is hemodialysis and how does it work? Who needs it? How do you prepare for it?


About The Kidneys

Your kidneys are the two kidney bean-shaped organs that are located in your lower back, or in your flanks. And the kidneys are responsible for filtering out or cleaning your blood. They get rid of excess waste, excess toxins, and excess fluids. If your kidneys stop functioning, then you develop renal failure or end-stage renal disease. Now, what most people do not realize is that if you don't have at least one functioning kidney, you cannot live unless you have some form of renal replacement therapy, which can be a kidney transplant or a form of dialysis, either hemodialysis or peritoneal dialysis (PD).


about kidneys


What is Hemodialysis?

Hemodialysis, or blood dialysis, is the filtering of your blood outside of your body. So, if your kidneys stop working properly, the hemodialysis acts as a substitute kidney. Now it's important to note that hemodialysis does not actually correct your own kidney function. It does not fix or treat your kidneys. It simply steps in and acts as a substitute kidney. The hemodialysis does the work that your kidneys are no longer able to do. It does so by removing the blood from your body, running it through the hemodialysis system, and then returning your same blood, only cleaned and with less fluid back to you.


What is The Dialyzer?

The dialyzer is actually the filter. It's the main powerhouse of the hemodialysis system, and it is what actually acts as the substitute kidney. In the dialyzer, you have these hollow fibers that run through it, and these fibers are bathed in something called dialysates, or dialysis fluid. The blood that's removed from your body runs through these hollow fibers and through tiny little pores, you have excess toxins like urea and other small molecules that are in your body in excess, like phosphorus and potassium. They are able to get filtered through the tiny pores and get bathed in the dialysate. Also, excess water or excess fluid that is in your blood is able to be filtered out. But what is kept in these fibers are the larger and important molecules, like your red blood cells and other proteins.

So what happens is your blood runs through the dialyzer, the excess toxins and water are filtered out. The things that you need like red blood cells are kept in, and then your same blood is returned to your body, only now it's been filtered. The dialyzer has done the work of your kidneys. Now, actual kidneys do this work 24 hours a day, seven days a week, but if you are on dialysis, you're not on it constantly as such.


what is a dialyzer


How Often Are Patients Treated With Hemodialysis?

Most patients who are on hemodialysis are on it between three and six hours, about three days a week, especially if they go to a center. And so, in order to make sure that you feel well and that you maintain proper electrolyte balances when you are on hemodialysis, you still have to do some work at home, such as fluid restriction or restriction of certain foods, like having limited phosphorus and limited potassium in your diet. You do all of these things to help to keep you feeling well in between dialysis treatments.


How Does Hemodialysis Work?

So when you are on dialysis, how does your blood get from your body to the hemodialysis machine and then back to your body? Well, it does so through tubes, and those tubes are connected to your access, and we'll talk about access in just a moment. But as far as the tubing, the tubing is connected to your body. There are two tubes. One tube is connected to your body, and it takes your blood and it pumps it through the dialysis system, through the hemodialysis machine, through the dialyzer, and then, once your blood is cleaned, then another tube returns your same blood, only cleaned and with fewer toxins, and less water, back to you. And so, this is a constant system that runs throughout your hemodialysis treatment. Again, usually between three and six hours.  What is the tubing attached to? Well, your dialysis access.


Types Of Hemodialysis Access

Arteriovenous Fistula or AV Fistula

The AV fistula is the gold standard as far as hemodialysis access is concerned because it gives you the most efficient hemodialysis and it is the least likely to be infected. In order to have an AV fistula, a vascular surgeon surgically connects an artery with a vein, usually in the arm, and once this connection heals, you have a shunt. And so, what happens is when you have hemodialysis, one of those tubings I talked about is connected to the arterial side. It takes the blood out of your body, runs it through the hemodialysis machine and filter, and then, through the other tubing, it runs it back to your body through the venous side.

Arteriovenous Graft or AV Graft

The AV graft is very similar to the AV fistula in that you still have a surgically connected artery and a vein, usually in the arm, but in the case where if you have veins that are rather thin or arteries that are thin and maybe too weak in order to really give you a properly functioning, substantial AV fistula, then the vascular surgeon may opt to add an artificial material in order to make that shunt a little stronger, or little more durable. And so, an AV graft is another option for dialysis access.


If you're in a situation where you need temporary dialysis, or if you have acute kidney injury, then you may have a temporary Vascath placed, and it's usually placed in a vein of the neck, the internal jugular vein, or it can be placed in the groin, or in the femoral vein. Now, we prefer to have catheters placed in the neck because the neck area is cleaner and less likely to get infected than the groin area. But, for long-term dialysis, we really prefer the AV fistula. If you have a Vascath, then it is placed directly into the vein, and the exit site is right there where the vein is.

For a longer-term catheter, you will have a permcath, or a permacath, and it also is typically placed either in the internal jugular vein or in the femoral vein.  But with the permcath, it's actually tunneled under the skin, so the exit site is not right there where your actual vein is.


what is hemodialysis


In other words, if you have the permcath, it will do better long-term than the temporary catheter, because it is a little less likely to get infected. If you have some bacteria or some germs to enter your body at the exit site of the permcath, instead of the vein being right there, the bacteria would have to travel in the tunnel before it gets to you, and so this can help to decrease the risk of infection. Either way, catheters still put you at a higher risk, long-term, for infection than the AV fistulas do.

If you do have a catheter, you really have to be careful about keeping it clean. You don't want it to get very wet or sweat on it. You also don't want it to get dirty or submerged in water. It's important that you do everything you can to avoid getting a catheter infection. When I was a fellow in nephrology, when I did my nephrology specialty training, one of my research projects was actually about catheters and how they give you an increased risk of infection, specifically something called vertebral osteomyelitis as compared to the other access AV fistulas and AV grafts.


Who Needs Hemodialysis Treatment?

How do you know if you need hemodialysis, and when is it time to prepare?  Well, if you follow up with your kidney doctor (nephrologist) regularly, he or she will be watching your labs. They'll be able to see those signs of your kidneys not functioning properly. They'll be able to see when you're creatinine is getting too high or when your EGFR, the estimated glomerular filtration rate is getting too low. And if you progress to CKD stage five, the last of the five stages of kidney disease, then it's really time to consider a kidney transplant or dialysis.

There are also some symptoms that you may feel when it gets to that point where having hemodialysis or a form of renal replacement therapy is necessary. You might notice a decreased appetite or food may have a really bad or metallic taste to it. You may even have a tremor or notice that you're having some difficulty walking. You may have some forgetfulness or some easy bruising, or you may notice that you have an odor to your breath. It may smell something like urine. These symptoms could indicate the need for hemodialysis. But you really don't want to wait to get to that point. You want to stay ahead of the problem. And that is why, by the time you get to CKD four, it's time for your nephrologist to have a discussion with you about which renal replacement therapy you would prefer.

Dr. Frita - Frita McRae Fisher, M.D.
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