Operational Medicine 2001
Field Medical Service School
Student Handbook

ENVIRONMENTAL HEAT INJURIES

FMST 0403

17 DEC 99

TERMINAL LEARNING OBJECTIVE(S):

1.      Given a heat casualty in a combat environment (day and night) and the standard Field Medical Technician supplies and equipment, manage environmental heat injuries per the references.  (FMST.04.03)

ENABLING LEARNING OBJECTIVES:

1.      Without the aid of reference materials and given a list of symptoms common to a heat injury, correctly identify the injury, per the student handbook.  (FMST.04.03a)

2.      Without the aid of reference materials and given a list of treatment for heat injuries, select the appropriate treatment for the identified injury, per the student handbook.  (FMST.04.03b)

3.      Without the aid of reference materials and given a list of preventive measures, select the preventive measure to prevent heat injuries, per the student handbook. (FMST.04.03c)

4.      Without the aid of reference materials and given the FMST Mike bag and a simulated heat casualty, identify, treat, and monitor the casualty, per the student handbook.  (FMST.04.03d)

OUTLINE:

A.     BODY TEMPERATURE REGULATION

1.      NORMAL HEAT REGULATION

a.       Body temperature is regulated by the thermoregulatory center in the hypothalamus

1.      The hypothalamus receives input from various thermal receptors located throughout the body.  From this input, it can then tell the body to either:

a)      Conserve body heat

b)      Increase heat dissipation

2.      The hypothalamus regulates the body’s core temperature instead of its surface temperature.

3.      Normal range of the body’s temperature is 35.9 – 37.4 degrees C ( 96.6 – 99.3 degrees F).

2.      MECHANISMS OF HEAT PRODUCTION

a.       Main Source of heat production is from metabolism

1.      The release of epinephrine and norepinephrine cause increased cellular metabolism

2.      Thyroid hormone increases cellular metabolism

b.      Fine involuntary actions can produce a 3 to 5 fold increase in body temperature

1.      Shivering

2.      Chattering of teeth

c.       Physical exertion – from voluntary muscle activity

3.      MECHANISMS OF HEAT LOSS

a.       Conduction

1.      The direct transfer of heat from one molecule to another.

a) Example – blood conducting heat from the core of the body to the outer

    surface.

2.      Minimal heat from the body is lost in this manner.

b.      Radiation

1.      The transfer of heat through the air or a vacuum

a) Example – heat from the sun is carried through radiation

2.      Environmental temperature must be less than that of the body for heat loss to occur.

3.      60 – 70% of body heat is dissipated by radiation.

c.       Convection

1.      The transfer of heat through the circulation of air currents.

2.      A layer of warm air tends to remain near the body’s surface

3.      The wind chill factor combines the effect of convection due to wind with the actual still-air temperature.

d.      Evaporation

1.      The use of body heat to convert water on the skin to water vapor. 

2.      Types:

a)      Insensible perspiration – water that diffuses through the skin independent of sweating

1)      Examples include loss of water through the mucous membranes

2)      Losses are increased in dry or arid environments

b)      Sweating

1)      Occurs through the sweat glands

2)      Is controlled by the sympathetic nervous system

3)      Is the only mechanism for heat loss when the temperature of the surrounding environment becomes greater than skin temperature

B.     HEAT INJURIES

1.      Heat Cramps

a.       Definition – slow, painful, skeletal muscle cramps and spasms usually in the muscles most heavily used, and last for 1 to 3 minutes

b.      Cause – Salt depletion that occurs when fluid losses are replaced by water alone

c.       Signs / Symptoms

1.      The muscles are tender

2.      The skin is usually moist

3.      Core temperature may be normal or slightly elevated

4.      There is always a history of vigorous activity preceding the onset of symptoms.

d.      Treatment

1.  Rest in a cool environment

2.  Drink an oral saline solution (0.9% Normal Saline solution, Gatorade)

3.  Rest for 2 –3 days with no exertional activities

2.      Heat Syncope

a.       Definition – a sudden episode of unconsciousness resulting from cutaneous vasodilation and subsequent hypotension.

b.      Cause

1.      Cutaneous vasodilation

2.      Hypotension

c.       Signs / Symptoms

1.      Systolic blood pressure usually less than 100 mm Hg

2.      Pulse is weak

3.      Skin is cool and moist

4.      Core temperature is normal or mildly elevated

d.      Treatment

1.      Place patient in a recumbant position

2.      Rest in a cool place

3.      Administration of fluids either by mouth or intravenously

3.      Heat Exhaustion

a.       Definition – A systemic reaction to prolonged heat exposure (hours to days) and is due to sodium depletion and dehydration

b.      Cause

1.      Salt depletion through intense sweating

2.      Replacement of body fluids with water and not electrolytes

3.      Prolonged heat exposure

c.       Signs / Symptoms

1.      Thirst

2.      Fatigue

3.      Nausea

4.      Oliguria

5.      Giddiness

6.      Delirium

7.      Gastrointestinal flulike symptoms

8.      The skin is moist, flushed

9.      Rectal temperature is usually over 37.8 degrees C (100 degrees F)

10.  Heart rate is elevated

11.  Signs of heat syncope and heat cramps may accompany heat exhaustion

d.      Treatment

1.      Rest in a cool environment

2.      Provide adequate fluid hydration, either orally or intravenously

3.      Salt replacement

4.      Restriction of activities for the next few days

4.      Heatstroke

a.       Definition – a severe, life-threatening failure of thermoregulatory mechanisms, resulting in an excessive rise in body temperature

b.      Cause

1.      Impaired heat loss mechanisms

c.       Signs / Symptoms

1.      Core body temperature greater than 41 degrees C (105.8 degrees F)

2.      Absence of sweating

3.      Loss of consciousness

4.      Dizziness

5.      Weakness

6.      Emotional lability

7.      Nausea and vomiting

8.      Confusion

9.      Delirium

10.  Blurred vision

11.  Convulsions

12.  Coma

13.  Skin is hot, flushed, and dry

14.  Vital signs

a)      Pulse is tachycardic and bounding

b)      Blood pressure may be elevated at first, then hypotension develops

d.      Treatment

1.      Maintain an adequate airway and ventilation

2.      Rapidly reducing the body core temperature (methods are discussed in Section #C)

a)      Care must be taken that the cooling methods used do not produce vasoconstriction or shivering which would decrease the cooling rate and increase heat production

C.     METHODS OF COOLING THE BODY

1.      DIRECT COOLING:

a.       Method of heat loss is through conduction.

b.      Items are placed around the body to assist in the dissipation of excess heat.

c.       Examples include:

1.      Applying ice bags to vascular areas of the body (axilla, groin, scalp, and neck regions)

2.      Wrapping the body in a cooling blanket

2.      IMMERSION:

a.       Method of heat loss is through conduction.

b.      Immerse the patient in a bathtub filled with cool room temperature water.  Do not immerse the extremities.

1)     Requires constant monitoring of the patient during the procedure

2)     This method is slow (10-40 minutes).

3)     May cause hypothermia if the patient is left in the water for too long.

4)     The use of cold water must be avoided:

a)      It could cause vasoconstriction, which would impede the rate of heat loss

b)      It could cause shivering, which would increase heat production

      3.  ROOM TEMPERATURE WATER MISTING:

a.        Method of heat loss is through conduction

b.      Procedures:

1.      Spray or mist a semi-nude heat casualty on a mesh hammock applying a film of water on skin.

2.      A fan may also be utilized to increase the effectiveness of this method.

3.      Advantages:

a.       Method is fast (3-10 minutes)

b.      Requires minimal monitoring of patient.

c.       This method does not require cold or ice water.  Ambient air temperature water is all that is required.

d.      Can treat multiple casualties simultaneously.

D.     PREVENTIVE MEASURES

1.      Education of Personnel

a.       Wearing of Proper Clothing 

1.      Personnel need to know what types of clothes to wear in warmer 

      environments

2.      The wearing of NBC suits or body armor adds aproximately 10 degrees to 

      the measured wet bulb globe temperature (WBGT)

                   b.  Proper Acclimatization

            1.  In some areas this may take from two to four weeks

            2.  Drink plenty of water

            3.  Gradual introduction of physical training program

       c.  Maintain Good Physical Conditioning and Health

1.      A person’s physical condition has been directly related to the susceptability   to heat related incidents.

2.      Predisposing factors may also play a factor in heat casualties

a)      Age

b)      Underlying medical conditions:

1)      Cardiovascular disease

2)      Diabetes

3)      Obesity

4)      Medications

E.      ADDITIONAL INFORMATION

1.      SECOND ATTACKS:

One attack of heat stroke predisposes an individual to a second attack.  This is because the hypothalamus is damaged and even after the patient recovers; the body may not repair the hypothalamus to its former effectiveness.  The patient will become more sensitive to heat stress.

      2.  MORTALITY:

Heat stroke is a medical emergency and mortality may be as high as 80%.  It is the cause for 5000 deaths per year of which two-thirds are 65 years or older.  A temperature greater than 108 degrees F may produce irreversible brain damage. 

F.  EVACUATION:

1.      Heat stroke patients in a field environment must be medically evacuated to a medical treatment facility.  During medevac, douse the patient with water and maintain free movement of air over the wet casualty.

2.      In an ambulance, leave doors and windows open to promote circulation.  In a helicopter, fly at cooler altitudes and leave doors open, if possible.

3.      Sedative drugs should be avoided because they disrupt an already malfunctioning heat regulating mechanism.  If convulsion occurs, Valium may be administered intravenously.

F.      HEAT CONDITION FLAG WARNING SYSTEM:

1.  Heat conditions are determined by the Wet Bulb Globe Temperature (WBGT)

     index, which is a single number derived mathematically from three distinct

     temperature measurements:

a.       wet bulb

b.      dry bulb

c.       globe temperatures

2.      Color-coded flags are used in implementing a flag warning system to help prevent heat casualties during hot weather.  These flags will be prominently displayed by all commands so that every one can see them, particularly in areas where physical training takes place.

3.      Instructions for use of Heat Condition Flag Warning System:

a)      When the WBGT index reaches the temperature indicated in the parenthesis below, the corresponding flag will be raised.  For example, the a WBGT index reading of 86 degrees F requires that a yellow flag be raised and strenuous exercise for unacclimatized troops in their first 2 or 3 weeks aboard their new duty station be suspended.

1)     WHITE FLAG (WBGT index of less than 80 degrees F).  Extremely intense physical exertion may precipitate heat exhaustion or heatstroke.  Caution is taken.

2)     GREEN FLAG (WBGT index of 80 degrees F to 84.9 degrees F).          

      Heavy exercises for unacclimatized personnel will be conducted         

      with caution and under constant supervision.

3)     YELLOW FLAG (WBGT index of 85 degrees F to 87.9 degrees F).  Strenuous exercises, such as marching at standard cadence, will be suspended for unacclimatized troops in their first 2 or 3 weeks.  Outdoor classes in the sun are to be avoided.

4)     RED FLAG (WBGT index of 88 degrees F to 89.9 degrees F).  All physical training will be halted for those troops who have not become thoroughly acclimatized by at least 12 weeks of living and working in the area.  Those troops who are thoroughly acclimatized may carry on limited activity not to exceed 6 hours per day.

5)     BLACK FLAG (WBGT index of 90 degrees F and above).  All strenuous outdoors-physical activity will be halted for all troops.

(a)    Wearing of body armor or NBC warfare protective uniforms in effect adds 10 degrees F to the measured WBGT index.  Heat conditions will be adjusted appropriately.

REFERENCE (S):

1.  First Aid for Soldiers                                                               

2.  Tactical Emergency Care                                                         

3.  Emergency War Surgery                                                          

4.  Pre-hospital Trauma Life Support                                            

5.  Advanced Special Operations Medical Training Course         

6.  Advanced Trauma Life Support                                               

7.  Wilderness Medicine Handbook

Field Medical Service School
Camp Pendleton, California

Approved for public release; Distribution is unlimited.

The listing of any non-Federal product in this CD is not an endorsement of the product itself, but simply an acknowledgement of the source. 

Operational Medicine 2001
Health Care in Military Settings

Home  ·  Military Medicine  ·  Sick Call  ·  Basic Exams  ·  Medical Procedures  ·  Lab and X-ray  ·  The Pharmacy  ·  The Library  ·  Equipment  ·  Patient Transport  ·  Medical Force Protection  ·  Operational Safety  ·  Operational Settings  ·  Special Operations  ·  Humanitarian Missions  ·  Instructions/Orders  ·  Other Agencies  ·  Video Gallery  ·  Phone Consultation  ·  Forms  ·  Web Links  ·  Acknowledgements  ·  Help  ·  Feedback

*This web version is provided by The Brookside Associates Medical Education Division.  It contains original contents from the official US Navy NAVMED P-5139, but has been reformatted for web access and includes advertising and links that were not present in the original version. This web version has not been approved by the Department of the Navy or the Department of Defense. The presence of any advertising on these pages does not constitute an endorsement of that product or service by either the US Department of Defense or the Brookside Associates. The Brookside Associates is a private organization, not affiliated with the United States Department of Defense.

Contact Us  ·  ·  Other Brookside Products