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|Diet, Hydration and SBS - Dr. Kelley|
Dehydration: Q&A with Dr. Darlene Kelly
The human adult body contains 60 percent and 55 percent water for women and men respectively. The brain and heart contain 73 percent water, the heart 83 percent, and even bone is 31 percent water, according to the U.S. Geological Service Water Science School. Therefore, when fluid balance is upset, the effect can be widespread throughout the body. This is of particular concern to consumers of home parenteral (HPN) and/or enteral nutrition (HEN) and those with short bowel syndrome (SBS).
Q1: Dr. Kelly, what is dehydration? What causes it?
Dehydration occurs when fluid losses (urine output, diarrhea/high ostomy output, sweat, breath, and other smaller fluid outputs) exceed fluid intake (liquids, water content of food, HPN, and other IV fluids*). It often occurs when there is watery diarrhea or high output from the ostomy, as may happen with diarrheal diseases. In SBS occurring after removal of sections of the small intestine with or without colon, sweets or high salt intakes can also cause excessive intestinal fluid loss. Other causes of dehydration include fever, vomiting, and medications (especially diuretics).
I often have described what would happen if someone were in the desert without a water supply. The kidneys try to hang on to fluid by decreasing urine output. The urine becomes concentrated (dark amber to brown) and the volume is decreased. Typically thirst is prominent and the individual would drink water when it is available. In the case of SBS, the water might actually be counterproductive (explained below).
The flip side of dehydration is over-hydration. Normally when fluid intake exceeds output, the kidney compensates by increasing urine volume. The analogy here is when people drink excessive amounts of fluid (beer?), they may find themselves in the restroom repeatedly to pass urine. However, in kidney insufficiency, this compensation may not be possible and excess fluid is not excreted. In that case, the person gains weight quickly. This can be of particular concern in either kidney or heart failure and is a reason to see a clinician immediately.
Q2: Why is dehydration a problem (short-term and long-term effects)?
The short-term effects are decreased urine output, weight loss, fatigue, increased thirst…often leading you to drink fluids, usually water. And, as noted above, drinking excessive “free” water can be counterproductive.
If dehydration is not evaluated and reversed, it can lead to much bigger problems. Chronic dehydration can lead to kidney stones, as well as kidney failure and the need for dialysis, sometimes followed by kidney transplant. Therefore it is preferable to avoid dehydration!
Q3: Are some people more susceptible to dehydration than others? Are there activities, conditions, or situations that make us more vulnerable?
Dehydration is one of the serious complications of SBS. This is usually because of increased intestinal fluid outputs with SBS.
When someone with SBS, especially in the absence of colon, eats a diet with high sugar and/or salt content (aka high osmolality intake), the concentration of the sugar and/or salt components pulls water from the bloodstream and cells in order to dilute the concentration within the shortened bowel. The same thing occurs in people with an intact small intestine and colon, but the intact colon has the ability to absorb water greatly in excess of the usual requirement, returning it into your system. Unfortunately the shortened bowel in absence of colon cannot reabsorb the fluids from the small intestine, and the fluids are flushed out of the system.
Activities in very hot weather cause fluid losses through sweat. This is why athletes are very careful to take in appropriate fluids when they anticipate exercise as well as during the exercise. Any diarrheal disease can cause dehydration, as can some kidney diseases that abnormally increase urine output.
Q4: Can I anticipate when dehydration may be a problem? What are the symptoms of dehydration?
When diarrhea is worsened and fluid is not replaced either orally or intravenously, dehydration is common. In very hot weather fluid losses are also prominent.
Rapid weight loss could be a sign that you are dehydrated. Since the first thing that happens is the kidneys decrease output, close attention to urine color is also important. A change in color from light yellow to dark amber and brown is a good clue that dehydration is developing, although dehydration is not the only possible cause for such a change. At that point, it is quite useful to measure the urine volume for twenty-four hours. The urine output that we aim for in our HPN practice is at least one quart daily. These findings (the rapid weight loss, decreased urine output, and dark urine) usually precede any changes measured in laboratory tests (particularly blood urea nitrogen [BUN] and creatinine).
Other symptoms and signs can include light-headedness, especially when you rise from a lying position; rapid pulse; excessive thirst; sunken eyes; dry mouth and eyes; fatigue; lethargy; and “tenting” of the skin. “Tenting” refers to lifting a bit of skin on the back of the hand; when it makes a tent-like shape that stays for several seconds, it indicates that the tissue is dry (dehydrated). While most of these signs and symptoms are non-specific (meaning that taken alone, none of them point specifically to dehydration), several of them occurring together in a person who is at risk may indicate dehydration.
Q5: I’ve been told I shouldn’t drink plain water. Why is that?
Plain water or “free water” has an extremely low osmolality, approaching zero, because it contains virtually no salts (sodium, potassium, chloride) or other components. By contrast, the fluid in the body contains high amounts of sodium and has an osmolality of about 300 mosomols. The body tries to maintain an equal distribution of sodium across membranes. Thus if sodium levels are high on one side of a membrane and nearly zero on the other side, the sodium will move across the membrane to where there is less sodium. Where sodium goes, water follows. Putting this into the context of the body, ingested water in the intestine will cause sodium from the blood side (high concentration) to move into the intestine, pulling water with it, which equals DIARRHEA! So in the case of SBS, water is a very poor hydrator because it causes loss of fluid (in diarrhea) greater than the amount of fluid (water) consumed. What you can do instead is drink oral rehydration solution!
Q6: What is an oral rehydration solution (ORS)?
ORS is a mixture of electrolytes (sodium, potassium, chloride, bicarbonate), carbohydrate (sugar or starch), water, and flavoring that is used to rehydrate people.
It is sometimes an alternative to huge IV fluid replacement.The components of ORS have to be in very specific ratios and in appropriate quantities to be effective. ORS was first used in cholera, the most severe and lethal diarrheal disease in the world. It occurs in large epidemics primarily in Third World countries, where it is particularly difficult to replace sufficient fluids intravenously and safely. The use of ORS in cholera has been called the most important medical discovery of the twentieth century. It has saved millions of lives. Much of this research was done in Bangladesh.
The World Health Organization (WHO) has been particularly involved in the development of ORS formulas. Over the years WHO has designed at least three mixtures for differing conditions that are being used extensively. There are also several commercially produced products available in the U.S. In addition, there are recipes that can be made at home from common food products, usually quite inexpensively. Oley has several ORS recipes available, including a WHO recipe (click here or request a copy at 800-776-6539).
Q7: How about caffeinated drinks, such as tea, coffee, sodas, or energy drinks? Are sports drinks good for me?
Tea and coffee are not only a version of “free water” (thus pulling sodium and water from the body into the intestine, equaling diarrhea), but they are also diuretics. Thus they are poor hydrators. Sodas, if sweetened with sugar, have an extremely high osmolality (the result of the sugar), so water is pulled into the intestine, resulting in diarrhea. In the case of diet beverages, they too are equivalent to “free water,” causing diarrhea. Energy drinks for the most part are high osmolality so are not a good choice for those with SBS. Some sports drinks are better than others for improving hydration. However, overall, they are not optimal. The osmolality is too low to be as effective as the best ORS formulas.
Thank you, Dr. Kelly!
* General principles apply to those on HEN, but some specific variability is not addressed in this article. For example, dehydration is affected by the amount of water in specific formulae, and osmolalities of different formulae are variable and have a big impact.
MY HPN module 3, “Fluid Balance”: This online module (available here) will teach you how to reduce your risk of developing dehydration or overhydration, as well as appropriate actions to take if one of these complications does occur. An HPN Nutrition Monitoring Log (which can be modified for HEN) is available as part of the module (or go directly to www.mdinformatics.com/MYHPN/Part3/HPN_monitoring.pdf).
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