Rick Curtis
Princeton University, Outdoor Action
Heat
injuries can be immediately life-threatening. Be aware of
the temperature conditions and your hydration levels.
The information provided here is designed for educational
use only and is not a substitute for specific training or
experience. Princeton University and the author assume no
liability for any individual's use of or reliance upon any
material contained or referenced herein. This article is prepared
to provide basic information about heat related illnesses
for t e lay person. Medical research is always expanding our
knowledge of the causes and treatment. It is your responsibility
to learn the latest information. The material contained in
this article may not be the most current. Copyright
© 1997 Rick Curtis, Outdoor Action Program, Princeton
University.
All the
body's fluids make up one large body fluid pool. Losses of
fluid from any one source is reflected in the levels of all
the body's other fluids: e.g. profuse sweating will ultimately
result in decreased blood volume. If a patient loses enough
fluid through any manner-bleeding, sweating, vomiting, or
diarrhea-the end result is the same: dehydration and, potentially,
volume shock. Adequate fluid is also critically important
in hot environments to help our body thermoregulate (see Heat
llnesses page 00). Remember, dehydration can kill!
If someone
is chronically losing fluid (from diarrhea or vomiting), then
you have a real emergency on your hands. Treat the cause of
the fluid lose as best you can (see Shock page 00, Bleeding
page 00, Heat Illnesses page 00, Abdominal Infections page
00) and rehydrate the patient. Be prepared to evacuate
your patient.
Dehydration
is always easier to prevent than it is to treat. So it is
important to ensure that all members of your group replace
their regular fluid losses by drinking adequate amounts of
water (see below). Your body absorbs fluids best when you
drink frequently and in small amounts rather than drinking
large amounts at one time. It also helps with fluid absorption
if you drink while eating. A pinch of salt and sugar in the
water will do if no food is available. Very dilute mixtures
of ports drinks like Gatorade® (add just enough to
taste) work well for this purpose.
Don't
depend on feeling thirsty to tell you when to drink. Thirst
is a late response of the body to fluid depletion. Once you
feel thirsty, you are already low on fluids. The best indicator
of proper fluid levels is urine output and color. You, and
all the people in your group should strive to be "copious
and clear." Ample urine that is light colored to clear shows
that the body has plenty of fluid. Dark urine means that the
body is low on water, and is trying to conserve its supply
by hoar ing fluid which means that urine becomes more concentrated
(thereby darker).
Basic
Fluid Recommendations
Season/Weather
|
Quarts/day
|
Explanation
|
Fall
& Spring Backpacking
|
2-3
quarts
1.8-2.8 liters
|
This
is what an average person will need on a daily basis
in general temperate conditions.
|
Hot
Weather Backpacking*
|
3-4
quarts
2.8-3.7 liters
|
In
hot and humid weather you are losing additional fluid
through sweating which must be replaced.
|
Winter
Backpacking*
|
3-4
quarts
2.8-3.7 liters
|
In
the winter time you are losing moisture through evaporation
to the dry air and especially through respiration.
Dry air entering the lungs heats up and is exhaled
saturated with moisture.
|
*All
Seasons
|
Add
1quart
1.8 liters
|
At
high altitude the body looses more fluid. Increase
your fluid intake if you are traveling at high altitudes
(over 8,000 feet/2,438 meters)
|
Table
9.1
Another
factor in overall fluid balance is the replacement of salts
lost to sweat. In most cases the salts found in normal food
consumption is adequate for salt replacement. In the event
of severe dehydration, a solution of ½ teaspoon
salt and ½ teaspoon of baking soda per quart/liter
of water can be used to replace lost fluid and salt. Use lukewarm
fluids. Discontinue the fluids if the person becomes nauseated
or vomits. Restart fluids as soon as the pers n can tolerate
it.
The body
has a number of mechanisms to properly maintain its optimal
core temperature of 98.6° F (37° C). Above
105° F (40° C) many body enzymes become denatured
and chemical reactions cannot take place leading to death.
Below 98.6° F (37° C) chemical reactions slow
down with various complications which can lead to death. Understanding
thermoregulation is important to understanding Heat Illnesses
and Cold Injuries.
- Vasodilation
- increases surface blood flow which increases heat loss
(when ambient temperature is less that body temperature).
- Vasoconstriction
- decreases blood flow to periphery, decreases heat loss.
- Sweating
- cools body through evaporative cooling
- Shivering
- generates heat through increase in chemical reactions
required for muscle activity. Visible shivering can maximally
increase surface heat production by 500%. However, this
is limited to a few hours because of depletion of muscle
glucose and the onset of fatigue.
- Increasing/Decreasing
Activity will cause corresponding increases in heat
production and decreases in heat production.
- Behavioral
Responses - putting on or taking off layers of clothing
will result in thermoregulation
Whenever
you go into an environment that is less than your body temperature,
you are exposed to a Cold Challenge. As long as your levels
of Heat Production and Heat Retention are greater than the
Cold Challenge, then you will be thermoregulating properly.
If the Cold Challenge is greater than your combined Heat Production
and Heat Retention, then you susceptible to a cold illness
such as hypothermia or frostbite.
Cold
Challenge - (negative factors)
- Temperature
- Wet
(rain, sweat, water)
- Wind
(see Table 9.3 Wind Chill Table)
Heat
Retention - (positive factors)
- Body
Size/shape - your surface to volume ratio effects how quickly
you lose heat.
- Insulation
- type of clothing layers
- Body
Fat - amount of body fat also effects how quickly you lose
heat.
- Shell/Core
Response - allows the body shell to act as a thermal barrier
Heat
Production - (positive factors)
Heat
Retention
|
+
|
Heat
Production
|
<
|
Cold
Challenge
|
=
|
Cold
Injury
|
Body
Size/shape
Insulation
Body Fat
Body shunting blood to the core
|
|
Exercise
Shivering
|
|
Temperature
Wetness
Wind
|
|
Hypothermia
Frostbite
|
Table
9.2
Wind
Chill can have a major impact on heat loss through convection
(see Chapter 2 - Equipment: Regulating Your Body Temperature).
As air heated by your body is replaced with cooler air pushed
by the wind, the amount of heat you can lose in a given period
of time increases. This increase is comparable to the amount
of heat you would lose at a colder temperature with no wind.
The Wind Chill factor is a scale that shows the equivalent
temperature given a particular wind speed.
In hot
weather, especially with and humidity, you can lose a great
deal of body fluid through exercise. This can lead to a variety
of heat related illnesses including Heat Exhaustion and Heat
Stroke. Heat Challenge is a combination of a number of external
heat factors. Balanced against this Heat Challenge is your
body's methods of Heat Loss (passive and active). When Heat
Challenge is greater than Heat Loss, you are at risk for a
heat-related injury (see Table 9.4). In order to reduce the
risk you need to either decrease the Heat Challenge or increase
your Heat Loss. Fluids are a central part of exercising in
a Heat Challenge (see Fluids above).
Heat
Challenge - (negative factors)
- Temperature
- Exercise
- Humidity
(see Table 9.5 Heat Index Table)
- Body
Wetness from sweating
- Wind
(see Table 9.3 Wind Chill Table)
Passive
Heat Loss - (positive factors)
- Body
Size/shape - your surface to volume ratio effects how quickly
you lose heat.
- Insulation
- type of clothing layers
- Body
Fat - amount of body fat also effects how quickly you lose
heat.
- Shell/Core
Response - allows the body shell to act as a thermal barrier
- Active
Heat Loss - (positive factors)
- Radiant
Heat from the body.
- Sweating
which causes heat loss through evaporation. Amount of sweating
is limited by:
- Fluid
Levels
- Level
of Fitness
Passive
Heat Loss
|
+
|
Active
Heat Loss
|
<
|
Heat
Challenge
|
=
|
Heat
Injury
|
Body
Size/shape
Insulation
Body Fat
Body shunting blood to the core
|
|
Radiant
Heat
Sweating
|
|
Temperature
Exercise
Humidity
Body Wetness
Wind
|
|
Heat
Syncope
Heat Exhaustion
Heat Stroke
|
Table
9.4
The
Heat Index:
Ambient
temperature is not the only factor that plays a role in creating
the potential for heat injuries, humidity is also important.
Since our bodies rely on the evaporation of sweat as a major
method of cooling, high humidity reduces our ability to cool
the body, increasing the risk of heat illnesses. The Heat
Index shows the relative effects of temperature and humidity
(see Table 9.5).
The
Heat Index
|
|
Environmental
Temperature Fº (Cº)
|
|
70º
(21)
|
75º(24)
|
80º(27)
|
85º(29)
|
90º(32)
|
95º(35)
|
100º(38)
|
105º(41)
|
110º(43)
|
115º(46)
|
120º(49)
|
Relative
Humidity
|
Apparent
Temperature Fº (Cº)
|
0%
|
64º(18)
|
69º(20)
|
73º(23)
|
78º(26)
|
83º(28)
|
87º(31)
|
91º(33)
|
95º(35)
|
99º(37)
|
103º(39)
|
107º(42)
|
10%
|
65º(18)
|
70º(21)
|
75º(24)
|
80º(27)
|
85º(29)
|
90º(33)
|
95º(35)
|
100º(38)
|
105º(41)
|
111º(44)
|
116º(47)
|
20%
|
66º(19)
|
72º(22)
|
77º(25)
|
82º(28)
|
87º(30)
|
93º(33)
|
99º(37)
|
105º(41)
|
112º(44)
|
120º(49)
|
130º(54)
|
30%
|
67º(19)
|
73º(23)
|
78º(26)
|
84º(29)
|
90º(33)
|
96º(36)
|
104º(40)
|
113º(45)
|
123º(51)
|
135º(57)
|
148º(64)
|
40%
|
68º(20)
|
74º(23)
|
79º(26)
|
86º(30)
|
93º(34)
|
101º(38)
|
110º(43)
|
123º(56)
|
137º(58)
|
151º(66)
|
|
50%
|
69º(20)
|
75º(24)
|
81º(27)
|
88º(31)
|
96º(36)
|
107º(42)
|
120º(49)
|
135º(57)
|
150º(66)
|
|
|
60%
|
70º(21)
|
76º(24)
|
82º(28)
|
90º(33)
|
100º(38)
|
114º(46)
|
132º(56)
|
149º(65)
|
|
|
|
70%
|
70º(21)
|
77º(25)
|
85º(29)
|
93º(34)
|
106º(41)
|
124º(51)
|
144º(62)
|
|
|
|
|
80%
|
71º(22)
|
78º(26)
|
86º(30)
|
97º(36)
|
113º(45)
|
136º(58)
|
|
|
|
|
|
90%
|
71º(22)
|
79º(26)
|
88º(31)
|
102º(39)
|
122º(50)
|
|
|
|
|
|
|
100%
|
72º(22)
|
80º(27)
|
91º(33)
|
108º(42)
|
|
|
|
|
|
|
|
Apparent
Temperature
|
Heat-stress
risk with physical activity and/or prolonged exposure.
|
90º-104º
(32-40)
|
Heat
cramps or Heat Exhaustion possible
|
105º-130º
(31-54)
|
Heat
cramps or Heat Exhaustion likely.
Heat Stroke possible.
|
130º
and up (54 and up)
|
Heat
Stroke very likely.
|
Caution:
This chart provides guidelines for assessing the potential
severity of heat stress. Individual reactions to heat
will vary. Heat illnesses can occur at lower temperature
than indicated on this chart. Exposure to full sunshine
can increase values up to 15º F.
|
Table
9.5
Heat
illnesses are the result of elevated body temperatures due
to an inability to dissipate the body's heat and/or a decreased
fluid level. Always remember that mild heat illnesses have
the potential of becoming severe life threatening emergencies
if not treated properly (See Fluid Balance above).
Heat
Cramps
Heat
cramps are a form of muscle cramp brought on by exertion and
insufficient salt.
Heat
Cramps Treatment
Replace
salt and fluid (see Fluid Balance) and stretch the muscle
(See Chapter 6 - Wilderness Travel & Camping: Stretching).
Kneading and pounding the muscle is less effective than stretching
and probably contributes to residual soreness.
Heat
Syncope
Heat
Syncope (fainting) is a mild form of heat illness which results
from physical exertion in a hot environment. In an effort
to increase heat loss, the skin blood vessels dilate to such
an extent that blood flow to the brain is reduced, resulting
in symptoms of faintness, dizziness, headache, increased pulse
rate, restlessness, nausea, vomiting, and possibly even a
brief loss of consciousness. Inadequate fluid replacement
which leads to dehydration contributes significantly to thi
problem.
Heat
Syncope Treatment
Heat
Syncope should be treated as fainting (See Fainting). The
person should lie or sit down, preferably in the shade or
in a cool environment. Elevate the feet and give fluids, particularly
those containing salt (commercial "rehydration" mix or ½
teaspoon salt and ½ teaspoon baking soda per quart/0.9
liter) (see Fluid Balance page 00). The patient should
not engage in vigorous activity for at least the rest of that
day. Only after s/he has completely re tored his/her body
fluids and salt and has a normal urinary output should exercise
in a hot environment be resumed (and then cautiously).
Heat
Exhaustion
This
occurs when fluid losses from sweating and respiration are
greater than internal fluid reserves (volume depletion). Heat
Exhaustion is really a form of volume shock. The lack of fluid
causes the body to constrict blood vessels especially in the
periphery (arms and legs). To understand Heat Exhaustion think
of a car with a radiator leak pulling a trailer up a mountain
pass. There is not enough fluid in the system to cool off
the engine so the car overheats. Adding fluid solves t e problem.
The signs
and symptoms of Heat Exhaustion are:
- Sweating
- Skin
- Pale, clammy (from peripheral vasoconstriction)
- Pulse
- Increased
- Respirations
- Increased
- Temperature
- normal or slightly elevated
- Urine
Output - Decreased
- Patient
feels weak, dizzy, thirsty, "sick," anxious
- Nausea
and vomiting (from decreased circulation in the stomach)
Heat
Exhaustion Treatment
Victims
of Heat Exhaustion must be properly re-hydrated and must be
very careful about resuming physical activity (it is best
to see a physician before doing so). Treatment is as described
above for Heat Syncope, but the person should be more
conservative about resuming physical activity to give the
body a chance to recover. Have the person rest (lying down)
in the shade. Replace fluid with a water/salt solution (commercial
"rehydration" mix or ½ teaspoon salt and amp;frac12;
teaspoon baking soda per quart/0.9 liter) (see Fluid Balance
page 00). Drink slowly, drinking too much, too fast very often
causes nausea and vomiting.
Evacuation
usually is not necessary. Heat Exhaustion can become
Heat Stroke if not properly treated (see Heat Stroke below).
A victim of Heat Exhaustion should have be closely monitored
to make sure that their temperature does not go above 103°
F (39° C) If it does so, treat the person for Heat
Stroke as described below.
Heat
Stroke - Hyperthermia
Heat
Stroke is one of the few life threatening medical emergencies.
A victim can die within minutes if not properly treated.
Heat Stroke is caused by an increase in the body's core temperature.
Core temperatures over 105° (41° C) can lead
to death. The rate of onset of Heat Stroke depends on the
individual's fluid status. To understand Heat Stroke think
of that same car pulling a trailer up a mountain pass on a
hot day. This time the radiator has plenty of flu d, but the
heat challenge of the engine combined with the external temperature
is too much. The engine can't great rid of the heat fast enough
and the engine overheats. There are two types of Heat Stroke-fluid
depleted (slow onset) and fluid intact (fast onset).
- Fluid
depleted - The person has Heat Exhaustion due to
fluid loss from sweating and/or inadequate fluid replacement,
but continues to function in a heat challenge situation.
Ultimately, the lack of fluid has minimized the body's active
heat loss capabilities to such an extent that the internal
core temperature begins to rise. Example: a cyclist on a
hot day with limited water.
- Fluid
intact (fast onset) - The person is under an extreme
heat challenge. The heat challenge overwhelms the body's
active heat loss mechanisms even though the fluid level
is sufficient. Example: a cyclist pushing hard on a 104°
F day (40° C).
Signs
& Symptoms of Heat Stroke
- The
key to identifying Heat Stroke is hot skin. Some
victims may have hot, dry skin, others may have hot, wet
skin because they have just moved from Heat Exhaustion to
Heat Stroke.
- Peripheral
vasoconstriction (skin gets pale)
- Pulse
Rate - increased
- Respiratory
Rate - increased
- Urine
Output - decreased
- Temperature
- increased (may be over 105° F/41° C)
- Skin
- may be wet or dry, flushed
- AVPU
- Severe changes in mental status and motor/sensory changes,
then the person may become comatose, possibility of seizures.
- Pupils
- may be dilated and unresponsive to light
Heat
Stroke Treatment
- Efforts
to reduce body temperature must begin immediately! Move
the patient (gently) to a cooler spot or shade the victim.
Remove clothing. Pour water on the extremities and fan the
person to increase air circulation and evaporation. Or cover
the extremities with cool wet cloths and fan the patient.
Immersion in cool (not cold) water is also
useful. During cooling the extremities should be massaged
vigorously to help propel the cooled blood back into the
core.
- After
the temperature has been reduce to 102° F (39°
C), active cooling should be reduced to avoid hypothermia
(shivering produces more heat). The patient must be monitored
closely to make sure that temperature does not begin to
go up again.
- Volume
replacement - the victim will probably need fluid regardless
of the type of onset.
- Basic
life support, CPR if needed.
- Afterwards
there can be serious medical problems. Prepare to evacuate
your patient.
- The
information provided here is designed for educational use
only and is not a substitute for specific training or experience.
Princeton University and the author assume no liability
for any individual's use of or reliance upon any material
contained or referenced herein. When going into outdoors
it is your responsibility to have the proper knowledge,
experience, and equipment to travel safely. The material
contained at the Web Site may not be the most current. This
material may b freely distributed for nonprofit educational
use. However, if included in publications, written or electronic,
attributions must be made to the author. Commercial use
of this material is prohibited without express written permission
from the author. Copyright
Disclaimer
and Reproduction Information: Information in NASD does not represent
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of the author and/or copyright holder. More
NASD Review: 04/2002
©1997, all rights reserved, Rick Curtis, Outdoor Action
Program, Princeton University.
|