By Maj. Darryn Bryant, 314 Medical Operations Squadron
/ Published June 24, 2009
LITTLE ROCK AIR FORCE BASE, Ark. --
Whether deployed to Southwest Asia or operating stateside during the summer heat, many military operations take place under extremely hot conditions. Because of the insidious nature of heat illnesses, heat injuries frequently result because people often don't recognize their symptoms until it's too late. Our body's protective cooling mechanism against heat injury is sweat. As long as we can sweat and the sweat can evaporate, we can continue to cool ourselves efficiently. If either the sweating mechanism begins to fail or the sweat cannot evaporate, then the cooling mechanism will fail, and heat injuries may occur.
On hot, humid days, our cooling is extremely inefficient, and it becomes relatively easy to overheat, because the sweat cannot evaporate. The evaporation of sweat accounts for 90 percent of our cooling ability.
Additionally, our ability to sweat diminishes as we become dehydrated. We lose body fluids in many ways every day. Sources of fluid loss include respiration, perspiration, urination and defecation. The loss rate from each of these will vary according to activity levels, air temperature, humidity and altitude. With normal daily activities, we typically lose about 1-2 liters just from respiration, and another 1-2 liters from normal perspiration. During heavy exertion, we can lose 8-10 liters of fluid over an afternoon of exercise or heavy activity. A 150-pound person can lose two percent of his body weight - three pounds - in fluid in just one hour! Because muscles are made up of about 70 percent water, this can definitely affect our ability to continue to do both aerobic and anaerobic work.
How much fluid do you need? One of the best ways to judge hydration status is to check the color of your urine: it should be relatively odorless and no darker than the color of straw. The rule of thumb is "clear fluids in, clear fluids out." A dehydrated person is more susceptible to developing a heat-related illness. Early symptoms of dehydration include thirst, fatigue, loss of appetite, lightheadedness and flushed skin. Later symptoms may include difficulty in swallowing, stumbling, numbness, blurred vision, painful urination, muscle spasms and delirium. It's extremely important to pay attention to these early symptoms so that heat illnesses can be averted. If it continues and goes untreated, heat exhaustion and heat stroke may occur.
Heat exhaustion is a condition caused by water and electrolyte loss. The primary cause of symptoms is related to the amount of sodium chloride (salt) lost. Symptoms can include excessive thirst, fatigue, exhaustion, nausea, muscle cramps, anxiety, agitation and headache. If treatment is further delayed, heat stroke may result. Heat stroke is a potentially life-threatening situation. Death can occur in less than 30 minutes. As the brain overheats, the person may become disoriented, combative, argumentative, and may hallucinate. Symptoms may also include seizures, vomiting and coma.
We assume that our sense of thirst will protect us from dehydration. This is not always the case. Our thirst sensation doesn't normally kick in until we are already two percent dehydrated! You don't want to wait until you feel thirsty to drink; it may be too late. Instead, design a fluid plan, just like you plan what you will be eating that day. Drink a couple of glasses of water with breakfast and throughout the morning, a couple at lunch, again in mid-afternoon, and then some more at dinner. A good rule of thumb is that you should drink at least 72 ounces of fluid every day. Obviously, if you're going to be exercising or working outdoors and sweating a great deal, you'll require much more fluid than this basic recommendation. The type of fluid is not nearly as important as the overall quantity, although water should be your first choice. Alcohol and caffeinated beverages are both diuretics, which can increase your fluid loss.
Here are some easy things you can do to protect yourself from heat injuries. Stay well hydrated by drinking fluids beginning about 12 hours before a scheduled work/exercise period. Our bodies can lose up to 2.5 quarts per hour, but can only absorb about one quart of water per hour. Carrying a clean, reusable water bottle can also be beneficial while at work, especially if you typically spend a lot of time outdoors. Pay attention to work/rest cycles and take frequent breaks from the outdoor heat. If possible, wear clothing that allows evaporation to help with the cooling process. Supervisors need to pay close attention to where their people are and what they're doing. Everyone should be able to recognize the early signs and symptoms of heat illness, so further progression can be avoided.
Can you drink too much water? The answer is yes. Perhaps you've heard of "water intoxication" incidents with U.S. military recruits and athletes at summer training camps. The military has traditionally focused on the dangers associated with heat illness, which have killed a number of healthy young enlistees. However, pushing the need to drink water too far can also have deadly consequences. Unfortunately, the dangers of over hydration are similar to those of dehydration! Over hydration can flush out critical electrolytes like sodium and potassium. Look for sweating, dizziness, fainting, flushed skin and possible unconsciousness. Here are a couple of examples:
- A 19-year-old Air Force recruit collapsed during a 5.8-mile walk, with a body temperature of 108 degrees Fahrenheit. Doctors concluded he died of heat stroke and low blood sodium levels because of over hydration.
- A 20-year-old trainee in the Army drank about 12 quarts of water during a two- to four-hour period while trying to produce a urine specimen for a drug test. She experienced fecal incontinence, became confused, lost consciousness, and died from swelling in her brain and lungs.
When we drink too much water, brain swelling can result. To prevent over hydration, stay hydrated, but limit your water intake to 1-1/2 quarts per hour, and 12 quarts total per day. If you suspect over hydration, call 911, as this is a medical emergency!
Heat injuries are preventable. It's up to everyone to continue to check each other to ensure no one succumbs to a heat-related illness, especially when conducting military operations under extremely hot conditions.