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Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Tips to Avoid Dehydration


In the June 6 edition of the San Francisco Chronicle, I wrote a column entitled "The Well-Watered Athlete." The column was derived from a longer piece that needed to be condensed a bit in order to meet the publication guidelines for the newspaper. For the sake of those who wish to have a bit more explanation, here is the longer version.

Dehydration, or depletion of body fluids, can swiftly debilitate athletes and outdoor enthusiasts. Anyone who ventures to high altitude, exercises in extremes of environmental temperature (hot or cold), or performs heavy exertion is at greater risk for dehydration. Staying well hydrated should be a top priority for participants and spectators alike.

When a person must rely on oral consumption of fluids, the limiting factor is how quickly liquids can be absorbed from the gastrointestinal (GI) tract. Since the maximum rate of stomach emptying (a surrogate for fluid absorption) is only 1.2 quarts per hour, it’s easy to understand how a person can become dehydrated when fluid losses exceed this amount. Most people are able to tolerate a 1 quart per hour sweat rate and manage rehydration with oral fluids. The same principle holds true if fluid losses are from diarrheal illnesses, which are common in adventure travelers.

Recall that world-class distance runners who are acclimated to heat can sweat in excess of 3 quarts per hour! However, only evaporated sweat contributes to efficient heat loss. Sweat that drips from the skin does not contribute to the cooling process, but certainly contributes to dehydration .

Dehydration is roughly estimated as follows:

Mild dehydration – thirst, dry mucous membranes (mouth, eyes), dry armpits, dark-colored urine, decreased sweating, normal pulse rate

Moderate dehydration – the above plus sunken eyes, doughy skin, weakness, scant darkened urine, rapid and weak pulse rate

Severe dehydration – the above plus altered mental status (confusion, delirium, fainting), elevated body temperature (if it’s hot outside), no urine, no tears, no sweating, collapse, dangerously low blood pressure

Most people underestimate their fluid requirements, so it is very important to replace liquids as soon as you can.

If fluid losses are expected, then hydrate prior to the situation. If exercising in an endurance event, assume that you will constantly be mildly dehydrated. Many sports beverages contain too much sugar for an optimal rate of GI absorption. If the beverage contains more than 2 to 2.5% glucose, dilute it with water to achieve approximately half that concentration. If you are in the wilderness and don’t have access to sports beverages or dry mix, you can prepare a homemade solution (1 quart of disinfected water plus ½ to 1 teaspoon of sodium chloride [table salt], and glucose [6 to 8 teaspoons of table sugar or 1 to 2 tablespoons of honey]). Each quart of this concoction should be alternated with ½ to 1 quart of plain disinfected water. Estimation techniques to measure powdered ingredients (such as a “pinch” of table salt) are notoriously inaccurate, which can be dangerous if you add excessive amounts. Use a proper measuring implement.

Oral Rehydration Salts (ORS) that meet World Health Organization standards are available in a dry mix; Cera Lyte 70 oral rehydration salts create a rice-based solution. One packet of either is mixed with a quart of water. After the solution is prepared, it should be consumed or discarded within 12 hours if kept at room temperature or 24 hours if refrigerated. Other choices that are quite palatable include Gatorade or CeraSport electrolyte-containing sports beverage.

If only fruit juice is available, remember to cut it to half strength with water. Coffee, tea, and alcohol-containing beverages cause increased fluid loss through excessive urination (diuretic effect) and should be avoided.

To limit dehydration, encourage frequent rest stops and water breaks. Try to ingest a quart per hour until the frequency of urination begins to increase the the urine color turns light or clear. The best indicators of adequate dehydration are clear, light-colored urine and absence of thirst. If the urine remains darkened or scant, then fluid requirements are not being met. Never rely upon thirst alone to guide fluid replacement.

Adequate water ingested during exercise is not harmful, does not cause cramps, and will prevent a large percentage of cases of dehydration and heat illness. The temperature of the fluid ingested should be cool, to promote transit through the stomach. It is a myth that ingesting cold fluid causes abdominal cramps, so long as the amount ingested is prudent. If large quantities of electrolytes are lost and not replaced (e.g., if large quantities of water are consumed without salt), a person can become quite ill.

Condition yourself for the environment. To acclimatize, gradually increase exercise in a hot environment for a minimum of an hour a day for 8 to 10 days. Children require 10 to 14 days. Acclimatization is manifested as increased sweat volume with decreased electrolyte concentration (more efficient sweating), greater peripheral blood vessel dilation (more efficient heat loss), lowered heart rate, decreased skin and core temperatures during exercise, increased water and salt conservation by the kidneys, and enhanced metabolism of energy supplies.

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Tags: Staying Safe

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.