HPR 010 Lecture Notes - Lecture 23: Cardiac Arrhythmia, Frostbite, Vasoconstriction
12 Jun 2018
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Chapter 20 Cold- Related Emergencies
Heat flows from an area with a high temp to an area with a lower temp.
How Cold Affects the Body
- Humans protect themselves from cold by avoiding or reducing cold exposure using clothing and
shelter. When that protection proves inadequate, the body has biologic defense mechanisms to
help maintain correct body temp. These mechanisms are vasoconstriction and shivering.
o Vasoconstriction is the tightening of blood vessels during cold exposure. It leads to
discomfort, numbness, loss of dexterity in the hands and fingers to conserve body heat.
But it leads to cold injuries.
o Shivering increases internal heat production and helps offset the heat loss. Shivering is
the ody’s ai involuntary defense against the cold. It produces heat by forcing muscles
to contract and relax rapidly.
o Internal heat production is also increased by physical activity; the more vigorous the
activity, the greater the heat production.
- Susceptibility to cold injuries can be minimized by maintaining proper hydration and nutrition;
avoiding alcohol, caffeine, and nicotine; and limiting periods of inactivity in cold conditions.
- Heat Loss From the Body
o Normal body temp is maintained by a balance of heat production and heat loss. Heat is
produced by food metabolism and muscle activity, and shivering can increase heat
production up to 500%. Shivering causes a large increase in heat production, but it rapidly
consumes calories stored in the liver and muscles as glycogen.
o Lak of food liits the ody’s aility to podue heat; he glyoge stoes ae depleted,
heat output decreases.
o Body heat loss can occur via 4 ways:
▪ Conduction, direct contact with colder object. Ex: immersion in cold water
▪ Convection, loss of heat from air blowing over skin or through clothes. Windchill
is the combined effect of the ambient temp and wind speed.
▪ Evaporation, conversion of liquid on the skin to a vapor
▪ Radiation, primary method, accounts for 65% of heat loss. Warm object radiated
heat to cooler air.
- Susceptibility to Cold Injury
o Unfit people are more susceptible to cold injury. They tire more quickly and are unable
to stay active to keep warm as long as people who are fit.
o Dehydration reduces blood flow in the skin, which increases susceptibility to cold injury.
o Fat functions as an insulator against heat loss b/c it has less blood flow that muscle and
loses less heat. So, a very lean person may be susceptible to the effect of cold if wet or
not dressed properly.
o Old people are less tolerant of the cold than young people b/c of decline in fitness, poor
circulation, illness, etc.
o Alcohol, and caffeine cause blood vessels to open, speeding up heat loss. Nicotine
decreases blood flow to the skin.
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- Effects of Altitude
o Temperatures, wind-chill, and the risk of cold injury at high altitudes differs from those at
lower altitudes. Air temp drops 3.6 degrees F every 1,000 feet. Winds are more severe
higher up with less cover, and people are more susceptible to frostbite.
- Effects of Water
o It can conduct heat away from the body much faster than air of the same temp. When
clothing becomes wet b/c of snow, rain, splashing water, or accumulated sweat, the
ody’s loss of heat is aeleated up to ties faste. Plugig ito cold water can cause
irregular heartbeat, gasping, and hyperventilation → leads to heart failure and drowning.
- Effects of Wind
o Potential for body heat loss, skin cooling, and decreases internal temp is increased. Wind
increases heat loss from skin exposed to cold air, in effect lowering the temp. the wind-
chill index integrates wind speed and air temp to provide an estimate of the cooling power
of the environment and the risk of cold injury
- Effect of Metals and Liquid Fuels
o Metals and liquid fuels can conduct heat away from the skin rapidly. Fuels and solvents
remain liquid at very low temperatures. Skin contact with fuel or metal at below freezing
temps can result in freezing instantly.
- Minimizing Effects of Cold on the Body
o Dress well, air is a good insulator and the basis for most clothes is to trap a layer of air
around the body. Layer up to stay warm.
o Three important layers
▪ 1st, inner layer removes perspiration from the skin
▪ 2nd layer insulates
▪ 3rd, outer layer protects against wind and water
Nonfreezing Cold Injuries
- Can occur when conditions are cold and wet, and the hands and feet cannot be kept warm and
dry.
- Chilblain is a nonfreezing cold injury that, while painful, causes little or no permanent damage.
o What to Look For: swollen skin, tender skin, hot skin, blisters, condition can worsen to an
aching, prickly sensation and then numbness
o What to Do: get out of the cold
- Trench Foot/ Immersion Foot: serious nonfreezing injury that develops when the skin on the feet
is exposed to moisture and cold for prolonged periods (12 hrs. or more). Can be causes by wearing
wet boots or shoes and socks. The combo of cold and moisture softens the skin, causing tissue
loss and infection.
o What to Look For: itching, numbness or tingling pain, swollen feet or pale skin, red or blue
blotches on the skin
o What to Do: dry the skin, rewarm the foot, care for open weeping area by cleaning
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