Why Do Dialysis Patients Need to Limit Potassium?

Why Dialysis Patients Need to Limit Potassium

By A. Peter Lundin, MD and Maureen F. Lundin, RN

Editor's Note: This article was written in 1993. Most of the information in the article remains true today, however portions of it may not be up-to-date. If you have questions about potassium and its recommended intake, please consult your healthcare professional.

If you are on dialysis, then you had better pay attention to how much potassium you can take in. Potassium, or K+, is usually found next to sodium (Na+) on your lab reports. You will hear a lot from the dietitian, doctor and nurses about how you must cut back on your intake of these and other substances. Except for sodium (salt), you may not notice any difference in the way you feel when your lab values rise into the forbidden zone, so why should you worry?

You should worry because too much (or sometimes, too little) of many things can harm you, if not immediately, then over a period of time. Too much phosphorus in your blood can cause your bones to weaken severely, although that can take years. Too much sodium will make you thirsty, so that you must either suffer or drink more fluid, which can strain your heart and make it difficult to breathe. Drink enough fluid and it will back up into your lungs, causing life-threatening pulmonary edema. Dangerous, but you will probably make it to the hospital and be treated successfully, at least the first few times. But potassium is the most dangerous substance, because too much of it will stop your heart - and it can happen suddenly, after you only feel a little weak in your body. When your heart stops beating, death follows.

Potassium is important for the function of your heart and muscles, and most of the potassium in your body is found in the cells of these organs. For your cells to function properly, it is important for your body to maintain a proper balance of potassium and sodium. Regulating this balance is the work of the kidneys. Since too much potassium presents a danger, the kidney extracts any excess from the body and excretes it in the urine. People with healthy kidneys do not need to restrict their potassium intake. In fact, potassium is good for them and foods high in it are often recommended as part of a healthy diet. People who are taking diuretics (water pills) for heart conditions are usually told to eat foods high in potassium to replace what they lose by the diuretic's action.

This situation is very different for people with poorly functioning or nonfunctioning kidneys. When your kidneys started making weak urine or stopped working at all, your body lost its ability to control its potassium level. This is when potassium can become dangerous for you. Instead of having two kidneys continuously filtering out excess water, potassium, sodium and poisonous waste products, you have an artificial kidney, which filters these substances only for several hours and only three times per week. If you are on peritoneal dialysis, you may have a closer approximation of a healthy kidney, if only in terms of its ability to eliminate potassium and water, and you can be more liberal in your potassium intake. Your intake becomes more like normal after a kidney transplant, when the transplanted kidney is working well.

Figuring out how much potassium you can safely eat and sticking to it is one of the biggest problems with being on dialysis. The necessary restrictions in the amount of salt and meat in your diet are, in fact, similar to those recommended to anyone who wants to eat a healthy diet. But the potassium restrictions just take a lot of pleasure out of eating, because so many of the foods that people like best contain large amounts of it.

There are things you can do, however, and things you should know that will make the limit on what you can eat less of a problem. First, be aware that the normal blood levels of potassium you see on your blood chemistry slip are not normal for dialysis patients. For unknown reasons, dialysis patients are not in danger of their heart stopping even when their blood level of potassium is up to 6.5 milliequivalents per liter (mEq/L). That level is as high as you should go, though. Using your blood chemistry level as a guide, you can learn with a little trial and error how much potassium-containing food you can safely consume. In order to do this, you need to be aware of what foods have a high amount of potassium so that your diet can be modified (see table on this page). Every dialysis patient should have a working knowledge of the most common foods high in potassium.

No food should be totally forbidden. You may have heard something like, "Never let a slice of tomato pass your lips." That kind of overstatement puts you into the position of "cheating" when you want to have even a bit. But no food is so dangerous that you cannot eat a little of it. It is just that potassium-containing foods, like those high in salt, need to be eaten with caution and in limited amounts, some more cautiously and with greater limitation than others. You also need to eat these foods in relation to the time you dialyze, being more careful in the hours and days after a treatment and increasing the amount as the time of your next dialysis draws closer. Don't make the mistake of thinking that because you eat a little of a banana or watermelon near the time of your next dialysis, that you can eat even more and still be safe. And remember, you can't dialyze out excess potassium until it is in your blood - that is, until the food that contains it is digested and absorbed from the intestine. So the time to eat that quarter of a banana or that chocolate is not while you are dialyzing, but several hours before you start your treatment. Pay attention to your predialysis potassium level and remember what you ate from the last dialysis to the next, so that you can make the proper adjustments. You will need to review this with your dietitian.

If your dietitian is after you for high potassium levels (greater than 6.5 mEq/L), but you feel you are watching your diet correctly, there may be a couple of other explanations for the high numbers. One cause is hemolysis (breakdown) of the red blood cells in the laboratory test tube. If the blood sits around too long in the tubes, or if it is allowed to rush in too fast from the syringe used to draw the sample, then some of the red blood cells can be destroyed. When this happens, potassium held in the cells will be released, making the levels artificially high. There are other causes for a false elevation of potassium that are important to be aware of and you should discuss them with your doctor.

Then there is always the possibility that you are, in fact, eating too much potassium. It is important that you be aware of this and able to admit to yourself that you are doing it. Remember, your potassium levels will not harm anyone but yourself. If you are taking in too much potassium, reduce your intake for the sake of your life.

This article originally appeared in aakpRENALIFE 1993, Vol. 8, No. 2.

© 1993 aakp. Used with permission. All rights reserved. No part of this publication can be reproduced without written permission from aakp