Dehydration and heat-related illness has long been a common
cause of mortality in outdoor situations. In 1967, during
the Israeli-Egyptian war, 20,000 Egyptians died due to dehydration.
However, there were minimal deaths of Israelis. This was partly
due to the fact that the Israelis were prepared. They each
had 5 gallons of water per day to drink, to replenish their
Dehydration is defined as sweat, urine or respiratory water
loss. It results from the voluntary restriction of intake
of water. Thirst is not a good indicator for when to replace
water. This has been seen in marathon runners who are accustomed
to running long distances and have conditioned themselves
thusly so. When endorphins take over, the thirst mechanism
is disregarded. So being thirsty is not a good indicator for
how dehydrated one might be. Dehydration also decreases work
"It is assumed that the total body
water (TBW) in the idealized 70-kg person is 42 L (about 60%
of body mass), and that two thirds of this water (28 L) is
intracellular and one third is extracellular (3.5 L of plasma
and 10.5 L of interstitial fluid). By calculation, the intravascular
or PV is equivalent to one twelfth of the total body water
(42 L TBW/12 = 3.5 L PV). It is further assumed that there
is no salt loss. Therefore TBW at the thirst threshold, compared
with euhydration, is calculated by:
Normal TBW x normal plasma = thirst TBW
x thirst plasma osm
42 L x 280 mOsm/kg = ? L x 295 mOsm/kg
11,760 mOsm/295 mOsm/kg = 39.9 L
That is, TBW at the thirst threshold is
Therefore the actual water loss to reach
threshold is 42 L - 39.9 L = 2.1 L, which represents nearly
3% of body weight ([2.1 kg/70 kg] x 100). By exercising in
the heat for only about 2 hours, one can incur an additional
water loss of 2.1 L (= 4.2 L total), which then results in
a water deficit equivalent to 6% of body mass. This 6% TBW
deficit decrements performance and increases risk of heat
illness." (Page 260, 261 Wilderness Medicine, Paul Auerbach,
You can lose 2% of your body weight before thirst is initiated,
which may get worse as the severity of dehydration increases.
With 4%-6% body water loss, you are anorexic, impatient and
you have symptoms of headache. With 10% loss, you have dizziness
and cyanosis. You also become light-headed and have syncopal
episodes. With 12% loss, you have difficulty swallowing and
you require assistance in re-hydration. 15%-25% water loss
Dehydration produces a decrease in ability to stay alert.
Your power can decrease 6% and time performance by 12% in
the heat. Sweat rates can be as high as 1-1/2 liters per hour,
or roughly 15 liters a day. Water requirements are not only
imperative in the heat, but they are imperative in the cold.
They are also higher than most people believe. At high altitudes,
water requirements can be very similar to those in the desert.
Some very rough estimates for water replacements in the cold:
Approximately 2 quarts per day, severe cold with heavy exercise,
up to 2 gallons. Altitudes above 10,000 feet, definitely more
than 2 gallons. Dr. Murray Hamlet postulates that one should
drink a little all the time, a lot at meals and at bedtime.
You want to be able to urinate pale yellow. If you can't remember
the last time you urinated, you are significantly dehydrated.
Drink by your watch in hot environments. Forced drinking in
the absence of thirst saves lives in the heat.
There can also be a cumulative effect of dehydration and
heat exhaustion which can occur over days, and is not recognized,
especially in athletics. This is commonly seen during the
month of August when football players train. The cumulative
effect is usually not taken into consideration.
We must entertain the idea of heat acclimation. What is heat
acclimation? The body can acclimate to a certain temperature
over a given period of time, where you can decrease your chances
of heat stroke and heat exhaustion. Working at 50% of your
maximum energy, 3 hours a day for approximately 9-12 days,
you can reach heat acclimation. Subsequently, certain construction
workers and athletics have definitely acclimated their bodies
to the point where they can decrease their chances of heat
stroke and heat injury.
The first organ to be hurt by heat stroke/exhaustion is the
liver. Liver enzymes will tell us whether or not this individual
is suffering from stroke vs. exhaustion for up to 24 hours
after the incident.
Dehydration and heat exhaustion and stroke can be very dangerous.
In the outdoors, it cannot be stressed
enough: If you cannot get to a clean water supply, GO AHEAD
AND DRINK THE WATER. It is best to re-hydrate yourself,
whether it is from creek, stream or lake. Your survival might
depend on it. When you are then found and get back to a location
where you can be treated, the healthcare professionals can
treat your symptoms at that point in time. For example, Giardia
Lambia, which is the very common organism that causes diarrhea,
the incubation for Giardia is approximately 3 weeks. You will
be found most likely in less time than that, and you are not
going to suffer any symptoms until you get back. So, hydration
is key. Please drink the water if you are in a situation that