Prevention and Treatment of Heat Illness

adapted from a presentation by:

Adam Anderson, M.D.
Emergency Medicine Physician
Wright State University Department of Emergency Medicine

viewable at: http://www.med.wright.edu/em/expo02.html

---

1. Temperature Regulation - Heat Transfer

Heat is always transferred from a higher to a lower temperature.

Four mechanisms of heat transfer:  conduction, convection, radiation, and evaporation.

Conduction:  direct contact between two surfaces

Convection:  gas or fluid flow over a surface

Radiation:  electromagnetic waves/solar

Evaporative:  one way flow from a wet surface to the environment

---

2. Methods of Temperature regulation

Automatic mechanisms:

Automatic body mechanisms are functional
up to a core body temperature to 107.6 degrees F

Sweating ­ up to 3.7 liters/hour (2-3 million sweat glands)

Metabolism ­ 70-100% released as heat

Blood vessel tone ­ directs flow

---

3. Methods of Temperature Regulation

Behavorial mechanisms:

Seeking shelter/shade

Seeking water

Shedding clothes

Resting

---

4. Factors that effect temperature regulation

Lack of sleep and/or fatigue

Dehydration

Lack of acclimatization

Alcohol/Drugs

Obesity

Other illnesses (heart disease, lung disease, diabetes, cancer)

Extremes of age

Medications (diuretics, blood pressure, antidepressants)

Smoking

---

5. Fluid and Electrolyte Basics

Minimal unavoidable daily water loss approx. 1.5 liters/day:

Sweat, Urine, Saliva, Tears, Breath, Feces

Most Important ­ Sweat

> 99% water with variable concentrations salt

(sodium chloride)

---

6. Prevention

Clothing

Activity

Hydration

Early Recognition

Acclimatization

---

7. Acclimatization

Physical not mental

Alterations in temperature regulation and salt- conserving mechanisms

Depends on:
-baseline physical fitness
-time in environment
-intensity of temperature
-activity in environment

---

8. Spectrum of Heat Illness

Heat syncope

Heat cramps

Heat exhaustion

Heatstroke

Four different illnesses!

---

9. Heat Syncope

Brief and temporary loss of consciousness

Remedied by horizontal position

Due to blood displacement to the extremities (not dehydration)

Temperature < 104 degrees F

Temperature usually normal

---

10. Field Management of Heat Syncope

Remove from environment

Horizontal position

Cooling Modalities

Encourage them to get off feet frequently

---

11. Heat Cramps

Due to salt depletion (sodium chloride)

Other minor symptoms:
Temperature < 104 degrees F
Temperature may be normal

Typical history:
Several hours of sustained exertion
Heavy sweating
Intake of large volumes of water

---

12. Field Management of Heat Cramps

Remove from environment

Use Cooling Modalities

Replace salt (sodium chloride)

Mild to Moderate Cramps:
14 to 12 teaspoon of table salt dissolved in a quart of water

Severe Cramps:
To emergency department for IV fluids containing salt

---

13. Heat Exhaustion

Generally develops over hours or even days

Usually unacclimatized individuals

Due to prolonged salt and water depletion

Variable symptoms: 

cramps, headache, dizziness, fatigue, anxiety, chills, nausea, vomiting,

increased heart rate and breathing, fainting

Temperature usually < 104 degrees F

Temperature may be normal!

---

14. Field Management of Heat Exhaustion

Remove from environment

Use Cooling Modalities

Begin salt and water replacement if able to drink

To emergency room for IV fluids if unable to drink

---

15. Heat Stroke ­ a true medical emergency!

Due to poor heat dissipation

Damage to almost any organ system:

Brain, Heart, Lungs, Liver, Kidneys, Blood Cells

10% Mortality

Classic Heat Stroke Symptoms:

Cessation of sweating

Temperature > 104 degrees F

Central nervous system disturbances:

(seizures/confusion/agitation/loss of consciousness)

---

16. Field Management of Heat Stroke

Call 9-1-1

Remove from environment

Begin Agressive Cooling Modalities

Begin salt and water replacement if able to swallow

---

17. Field Management Summary

Prevention and early recognition key

If suspect heat stroke call 9-1-1!

Goals for all heat injury/illness:

Remove from environment

Cooling Modalities

Begin water and salt replacement

When in doubt seek medical attention

---

17. Field Management - Cooling Modalities

Maximize Evaporative Cooling (wetting)

Minimize Shivering (produces metabolic heat)

Goal: Rectal Temperature < 102 degrees F

Mist/Fanning

Ice/Cold Water Immersion

Ice packs under arms, between legs

Do not use fever reducing medications:
·Tylenol, Ibuprofen, Aspirin

---

18. Field Management - Salt and Water Replacement

Hydration before activity:
8 oz water 10 to 15 minutes before physical activity

Hydration during activity:
8 to 12 oz water every 20 to 30 minutes during exercise

Do not need to routinely add salt

Sports drinks no better than water

Goal is clear urine

---

19. Emergency Department

What to expect ­ depends on severity of heat illness
Minimum ­ IV, IV fluids, blood work
Heat Stroke
Breathing tube and ventilator
Continuous rectal thermometer
Aggressive cooling modalities
Stomach tube
Bladder tube

---

References
Auerbach PS (ed). Wilderness Medicine: Management of Wilderness and Environmental Injuries. 1995:3