Rehydration and Fluid Replacement

Everyone knows it is important to rehydrate if sweating profusely after strenuous activity. However, determining the amount of fluid intake necessary to offset this fluid loss can be difficult.

It is important to note that cool fluids are more beneficial than warm fluids when rehydrating. There is no data available to support the fact that cool fluid intake while exercising causes intense stomach cramping.

If fluid loss has accelerated to the point of heat illness, I.V. fluid replacement is the treatment of choice. However in wilderness settings, that is not always possible.

Please note: Potassium intake should NOT be started until serum electrolyte levels are available. This is important because many commercial drinks being marketed today do contain potassium; it vitally important to understand how your body is affected by what you are put into it. Remember: As indicated by Dr. Auerbach, YOU CANNOT RELY ON THE THIRST MECHANISM TO PREVENT DEHYDRATION.
Many times, the thirst mechanism does not work as efficiently as we might think. After strenuous activity, there should be mandatory scheduled breaks every 20-30 minutes including fluid intake. If done routinely, we’d have fewer deaths on the athletic field due to heat stroke/illness resulting from dehydration.

Fluid replacement beverages

With the emphasis on physical fitness in the United States, targeting an overweight population, commercial drinks have become extremely popular, with companies vying for greater commercial time to increase their sales. There is much confusion regarding the great variety of drinks being marketed. Which are better for fluid replacement? Is it better to replace electrolytes or increase carbohydrates? Is one of greater importance than the other? Without getting into the major physiologic details when comparing the gastric absorption of carbohydrates and electrolytes, per the 1996 American College of Sports Medicine’s guideline for replacing carbohydrates, carbohydrates should be ingested at the rate of 30-60 grams/hour to maintain oxidation. To my knowledge, this guideline has not been challenged.

Sports drinks should contain about 5-10% of carbohydrates in the form of glucose or sucrose to enhance endurance. Many athletes suffer from cramps, nausea and diarrhea after drinking 10% glucose solution, per Dr. Auerbach. Research studies across the board indicate that when engaging in prolonged, strenuous activity, there should be fluid intake every 15-20 minutes, or approximately one quart/hour.

Drinking carbohydrates during prolonged exercise may enhance the performance of athletes. As per Dr. Auerbach, carbohydrate containing beverages SHOULD NOT be placed into canteens, or metal containers since microbial contamination would be inevitable.

In closing, clearly everyone knows that we need to replace our fluids during prolonged exercise.

1. Don’t rely on your thirst mechanism to alert you to your need for rehydration. Rehydrate every 15-20 minutes whether you want to or not.
2. There are not a lot of differences between sports drinks for rehydration purposes.
3. You do not need to replace potassium to any great extent.
4. You want to hydrate at about one quart/hour during heavy exercise. Obviously one must take into consideration environmental conditions such as heat and humidity, and your endurance level, including body’s ability to acclimate.
5. Know the differences between dehydrations symptoms, heat stroke symptoms, heat exhaustion symptoms and hyponatremia (sodium loss).
6. In the outdoors, if you observe anyone experiencing mental confusion, this should be considered a medical emergency, with heat stroke the mostly likely cause.
7. In moderate to severe dehydration, when replacing fluids, drinking large amounts of fluids and gulping frequently leads to extreme nausea and emesis (vomiting). You can still rehydrate, yet avoid potential vomiting, even in children, by taking in frequent, but very small amounts of fluid. Even if it is a tablespoon of fluids every 15 minutes, this will decrease the load on the gut, and decrease the nausea/vomiting factor.

For further details on direct physiology of dehydration, rehydration and fluid replacement, please review Wilderness Medicine by Auerbach, which is a great reference.