Defeating Dehydration

By Frederick E. Tilton, M.D.; FAA Federal Air Surgeon
Reprinted with permission from FAA Safety Briefing

Summer is prime time for flying. It is also a prime time for dehydration, given the combination of higher ambient temperatures, higher humidity, and warm winds. Certain beverages, e.g., coffee, tea, and soft drinks, can further increase the risk of dehydration. Since dehydration can produce headache, fatigue, cramps, sleepiness, and dizziness, it can put pilots at increased risk for incidents and accidents.

Four Quarts a Day Keep Dehydration at Bay

The amount of water you need to drink depends on work level, temperature, humidity, personal lifestyle, and individual physiology. The standard guideline for proper hydration, though, is to drink two to four quarts of water every 24 hours. Another way to measure your intake is the familiar eight-glasses-a-day guide: If each glass of water is eight ounces and you drink eight glasses, then you end up with 64 ounces or two quarts.

As with every other aspect of your health, the key is to be continually aware of your condition. Most people become aware of being thirsty with a 1.5-quart deficit. This level of dehydration triggers the “thirst mechanism.” The problem, however, is that the thirst mechanism does not trigger until you are already dehydrated. In addition, the body’s thirst mechanism is too easily turned off by drinking just a small amount of fluid. By the time you feel thirsty, you already have a significant fluid deficit, and if you drink only enough to make the sensation of thirst disappear, you are merely delaying the much needed replacement of body fluid.

Stages of Heat Exhaustion

Dehydration alone can create insidious hazards to your health, as well as to your safety as a pilot. There is, however, a more serious danger. If you do not remain aware of environmental conditions and your personal physiological status, you can progress to heat exhaustion, even if you maintain the necessary water intake for proper hydration.

There are three stages of heat exhaustion, and transition from one to another is not necessarily obvious. The first, heat stress, is characterized by a body temperature from 99.5 degrees to 100 degrees F. At this level, the pilot may experience reductions in alertness, performance, dexterity, coordination, and visual capability.

In the second stage which involves a body temperature of 101 degrees to 105 degrees F, the pilot experiences more obvious fatigue. Other effects can include nausea/vomiting, giddiness, cramps, rapid breathing, or fainting. These are not good at any time, but are especially dangerous when piloting an aircraft.

The third stage, a body temperature above 105 degrees F, is heat stroke. In this condition, the body’s heat control mechanism stops working. The pilot can experience mental confusion and disorientation and may exhibit bizarre behavior. At its worst, heat stroke can produce a coma.

Awareness and Prevention

Here are a few suggestions for awareness and prevention of dehydration and heat exhaustion:

• Drink cool (40 degrees F) water.
• Don’t rely on the thirst sensation as an alarm...
  stay ahead of the thirst curve.
• Be extra vigilant about hydration while exercising.
• Monitor your individual effects of aging or illness.
• If you feel lightheaded or dizzy, call it a day.

Fly safely, and never pass up an opportunity to have a fresh glass of water!

Dr. Tilton received both an M.S. and a M.D. degree from the University of New Mexico and an M.P.H. from the University of Texas. During a 26-yearcareer with the U.S. Air Force, Dr. Tilton logged more than 4,000 hours as a command pilot and senior flight surgeon flying a variety of aircraft. He currently flies the Cessna Citation 560 XL.