Thermal Protection and Hypothermia Considerations

Introduction

Thermal protection is paramount for undersea recreation, effective work, and military warfare needs. Heat loss is accentuated by many factors including the increased thermal conductivity of water as compared to air of the same temperature. The study of immersion hypothermia has increased survivability in downed pilots and aircrew, shipwreck victims, sport scuba enthusiasts, and near-drowned victims.

Where does the body lose heat ?

Head, neck, axilla, and inguinal region, for the most part
50 % lost from the head and neck alone heat flux across the skull, blood vessels close to surface
Remember children lose heat quicker because of ratio of body mass to skin surface
How does the body lose heat ?
Conduction-the transfer of heat by direct contact with water, air or ground
Convection-the transfer of heat by air or water that moves away
Radiation-the transfer of energy by non-particulate means, heat loss from an unprotected head
Evaporation conversion of water droplets (sweat) Into water vapor, thereby absorbing calories of heat

How do we protect these heat-loss areas?

Create a micro-climate around body with insulators
Waders, gloves, hats, boots, shoes
Wet suits made of closed cell neoprene
Dry Suits and under garments
Clothing In layers, virtues are loose fitting, air trapping, no ligatures, belts, zippers
Head coverings

What are some of the factors affecting how fast we lose heat?

Water Temperature
Outside Air Temperature (OAT)
Wind, wind-chill
Wave action, sea state
Wet clothes versus dry (5 times greater loss)
Body habitus
Sexual differences
Age
Air versus water (water 25 times greater loss)
Breathing Gas, air helium
Activity level, breathing rate
Fear, panic
Tachycardia
Fight or flight

What are some medications and conditions that increase heat loss?

Beta blockers
Phenothiazines
Benzodiazepines
Barbiturates
Effect of alcohol
Cigarettes
Metabolic states, thyroid function, or other medications
Sepsis
Nutritional state
Adaptation, “Polar Bear Clubs”
Ability to shiver

Have there been any studies about cold immersion?

Modern studies

University of Victoria “U-VIC” physical education majors; Determinants of effective working suits,
U S Coast Guard Cape Disappointment and Cape May, New Jersey Studies; Special considerations for survival suits, flying suits

Prognostic Factors recently published:
JAMA October 10, 1990 Vol 264, No. 14, Hyperkalemia a Prognostic Factor During Acute Severe Hypothermia
JAMA ibid above. Editorial Some People Are Dead When They Are Cold And Dead.
*Outlines from Lectures presented at Medical Seminars, May, 1991
*Adapted from M.J. Nemiroff, M.D.

AUTHOR

Ernest S. Campbell, M.D., FACS

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