FMST Student Manual - 2008 Web Edition*

TERMINAL LEARNING OBJECTIVES

1.      Given a heat casualty in a combat environment and the standard field medical equipment and supplies, manage environmental heat injuries, to prevent further injury or death per the references. (FMST-HSS-1403)

ENABLING LEARNING OBJECTIVES

1.      Without the aid of references, given a description or list, identify the predisposing factors associated with heat injuries, per the student handout. (FMST-HSS-1403a)

2.    Without the aid of references, given a list of symptoms, identify the type of heat injury, per the student handout. (FMST-HSS-1403b)

3.    Without the aid of references, given a description or list, identify the proper treatment for the heat injuries, per the student handout. (FMST-HSS-1403c)

4.     Without the aid of references, given a list, identify preventive measures for heat injuries, per the student handout. (FMST-HSS-1403d)

5.     Without the aid of references, given a simulated heat casualty and standard field medical equipment and supplies, manage the casualty, per the student handout.  (FMST-HSS-1403e)

1.  OVERVIEW  

From 1979 to 1999, there were over 8,000 heat related deaths in the United States.  More deaths than hurricanes, lightning, tornadoes, floods, and earthquakes combined.  High internal temperatures produce stress on the body, which, if not effectively counterbalanced, may result in heat injury or death.  Environmental as well as physiological factors influence the body's thermal equilibrium mechanism.  

Heat injuries can occur anywhere and at anytime of the year, depending upon physical activity and clothing worn.  However, heat injuries most frequently occur during warm weather training and operations due to exposure to high temperatures, high humidity, and sunlight.  Sweating increases daily water requirements as well as electrolyte replacement.  Dehydration leads to added heat stress, increased susceptibility to heat injury, reduced work performance, and degraded mission capability.

2.      BODY TEMPERATURE REGULATION

Body temperature is regulated by the thermoregulatory center in the hypothalamus.  The hypothalamus receives input from various thermal receptors located throughout the body.  From this input, it can then tell the body to either conserve body heat or increase heat dissipation by increasing cardiac output, respiratory rate, vasodilation, and perspiration.

The hypothalamus regulates the body’s core temperature not the body’s surface temperature.  Normal body temperature range is usually 97.6° - 99.6°F.  

3.      PREDISPOSING FACTORS ASSOCIATED WITH HEAT INJURIES

Physiological (Host) Factors

Fitness and Body Mass Index - low levels of physical fitness will reduce tolerance to heat exposure.  Being physically fit provides a cardiovascular reserve to maintain cardiac output as needed to sustain thermoregulation. 

Age - thermoregulatory capacity and tolerance to heat diminish with age.  However, this state can be improved by maintaining a low body weight and high level of physical fitness. 

Medical Conditions - mild form of heat illness seen in individuals is “prickly heat rash” and has been shown to cause reduced heat tolerance.  Other medical conditions that can increase the risk for heat intolerance and heat illness are diabetes mellitus, thyroid disorders, and renal disease.  Cardiovascular disease and circulatory problems that increase cutaneous blood flow and circulatory demand are aggravated by heat exposure.

Previous History of Heat Injury - personnel who have a history of heat injury (heat cramps, exhaustion, and stroke) are highly susceptible to repeated heat injury.  This is because the hypothalamus is damaged.  Even after the patient recovers, the body may not repair the hypothalamus to its former effectiveness, therefore, the patient will become more sensitive to heat stressors.

Skin Trauma - the skin is the largest organ of the body.  It serves as a layer of protection, controls the invasion of microorganisms, maintains fluid balance, and helps regulate temperature.  Personnel suffering from skin conditions that hamper the heat regulatory mechanism (sunburn, heat rash, windburn, and dermatologic disease) have an increased risk of heat related injuries.

Medications - the use of specific prescription or over-the-counter medications can place individuals at a greater risk for heat illness (see figure 1).  Certain medications can increase metabolic heat production, suppress body cooling, reduce cardiac reserve, and alter renal electrolyte and fluid balance.  Sedative and narcotic drugs will affect mental status and can affect logical reasoning and judgment, suppressing decision-making ability, when the individual is exposed to heat. 

Environmental Factors

Ambient Air Temperature - when the air temperature is above the body temperature, the body can only dissipate heat by sweating causing the heat to be slowly carried away by evaporation at the skin surface.  When air temperatures are below the body temperature, heat loss to the surrounding environment is rapid.

Wind Velocity - the higher the wind velocity, the faster the heat loss.  High wind velocity can produce windburn, which can have an adverse effect on thermal regulation.

Humidity - when the moisture content (humidity) of the air is high, sweat evaporates slowly and the rate of heat loss is greatly reduced.  When the humidity of the air is low, sweat evaporates more quickly therefore increasing the rate of heat loss.

Radiant Heat - heat produced by the reflective energy of the sun or equipment in close proximity to the human body.  Radiated heat is absorbed into the surrounding air and/or into the body.  The body's ability to cool itself is hampered. 

4.      TYPES OF HEAT INJURIES

Heat Cramps - slow, painful, skeletal muscle cramps and spasms usually in the muscles most heavily used (legs and abdomen) and usually last for 1 to 3 minutes.

Cause - salt depletion that occurs when fluid losses are replaced by water alone.  There is always a history of vigorous activity preceding the onset of symptoms.

Signs and Symptoms

- Muscle cramps and tenderness (extremities and abdomen)

- The skin is usually moist, pale, and warm

- Core temperature may be normal or slightly elevated

Treatment

- Rest in a cool environment

- Drink a sports drink or other drinks with salt (e.g., tomato juice)

- Massage and stretch affected muscles

Heat Exhaustion - the most common heat-related disorder.  A systemic reaction to prolonged heat exposure (hours to days) and is caused by excessive heat strain with inadequate water intake. 

Cause

- Salt depletion through intense sweating

- Replacement of body fluids with water and not electrolytes

- Prolonged heat exposure

Signs and Symptoms - distinguishing severe heat exhaustion from heat stroke may be difficult, but a quick mental status assessment will help determine heat stroke (see figure 2).  Any of the signs and symptoms of heat cramps may accompany heat exhaustion along with:

- Headache

- Fatigue

- Dizziness

- Hyperirritability/Anxiety

- Nausea

- Oliguria (decreased urine output)

- Heavy perspiration         

- Hyperventilation (rapid/shallow)

- Tachycardia

- Orthostatic hypotension

- Moist, pale, clammy skin