What Is Dialysis? All You Really Need to Know

As mentioned previously, I have a little background in medicine. And the kidneys are kind of my thing. Of course, I’ll admit that kidney disease isn’t the sexiest topic around—heart disease and cancer get way more love from the general public. In fact, not many people even know what a nephrologist is. (That’s a kidney doctor.) But kidney disease is one of the leading causes of death worldwide, making it pretty important. When kidney function gets bad enough, something called dialysis can become necessary. What is dialysis? Here’s all you really need to know.

 

A Brief Reminder

The kidneys are two bean-shaped organs responsible for removing waste products and excess fluid from the bloodstream. Whatever is not needed is excreted in the form of urine. The kidneys are also involved in the production of red blood cells (which carry oxygen) and active vitamin D (which is important for bone health among other things).

As kidney function declines, waste products and fluid can accumulate, leading to symptoms such as nausea, fatigue, swelling in the legs, and shortness of breath from fluid in the lungs. Similarly, a low red blood cell count (anemia) and an insufficient active vitamin D level can be seen. If severe enough and irreversible, the term end-stage kidney disease (ESKD) is applied.

With ESKD, an alternative strategy is required to perform what the kidneys are no longer adequately doing. This alternative strategy is dialysis, also sometimes called kidney replacement therapy. (It should be noted that dialysis can also be used in the case of acute kidney injury that may be reversible, but the focus here is on ESKD.)

 

Dialysis

Since dialysis attempts to replace kidney function, it must accomplish two things, namely waste removal (or clearance) and fluid removal (or ultrafiltration). The treatment can be provided in one of two main ways.

Hemodialysis

The prefix hemo- refers to blood. In this type of treatment, blood is removed from the body, run through an artificial filter (also called a dialyzer or membrane), and returned to the body. Access to the bloodstream is obtained with a catheter or a more specialized (and safer) creation such as an arteriovenous fistula or arteriovenous graft. As blood passes through the dialyzer, waste products diffuse out of the blood via small pores in the membrane, thus providing the aforementioned clearance. A negative pressure applied to the dialyzer allows for excess fluid removal from the blood, providing the aforementioned ultrafiltration.

Hemodialysis treatments can be provided in a dialysis center, typically three times a week, or at home, typically four or five times a week. Each treatment generally lasts anywhere from three to five hours, depending in part on patient size.

Peritoneal Dialysis

With peritoneal dialysis, no blood is removed from the body, and the membrane used is actually a naturally occurring membrane in the body called the peritoneal membrane. In this type of treatment, fluid (or dialysate) is instilled into the abdomen via a catheter. Waste from the body then diffuses through pores in the peritoneal membrane into the dialysate, providing clearance. The high sugar concentration of the dialysate drags water across the peritoneal membrane (via osmosis), providing ultrafiltration. After several hours, the dialysate is removed, and the process is repeated.

Peritoneal dialysis is done at home, usually every day of the week. At times, a bedside machine can be used to instill and remove dialysate while one sleeps, eliminating the need to perform the process manually.

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In both types of dialysis, the clearance provided does not match that provided by two healthy kidneys. Similarly, not all molecules removed by healthy kidneys are removed by dialysis. In most cases, medications to boost red blood cell production and replace active vitamin D are required.

 

Other Information

The life expectancy of someone on dialysis depends largely on the presence or absence of other health problems. In other words, a patient with advanced diabetes and heart disease will have a much shorter life expectancy on dialysis than a patient with minimal health problems (aside from the kidney disease).

Kidney transplantation is an option for some patients. That determination is made by a transplant center with highly specialized expertise. Unfortunately, given the limited number of available kidneys, wait times for transplant can be several years. During the wait, other health problems can develop, sometimes making a once transplant-eligible patient no longer eligible.

 

Far superior to any of the above is avoiding ESKD in the first place. Unfortunately, not everyone headed towards dialysis can escape that fate. But if you can, I highly recommend that you do.