Heat Loss Happens

The body produces heat. Heat is energy and energy tends toward equilibrium. In other words, heat flows from high energy density toward lower energy density. If the environment is on average at a lower energy density than the body, then heat will flow away from the body to the environment.

Heat loss occurs by several mechanisms

• Conduction - is basically the transfer of energy into and throughout a solid.
  • The amount of energy transferred is dependent upon the energy gradient
  • The rate of energy transferred is dependent upon surface area of contact and the conductivity of the materials
  • Conductivity depends on how easily one molecule of the conductor can pass energy to its neighbor molecule. Conducting molecules (metals) exchange energy easier than insulators (plastic, wood or cotton).
  • Conduction heat loss can be minimized by placing insulators between the patient and good conductors. Air, cotton, plastic and wood are common insulators.
    
    
• Convection - is energy transfer through a fluid such as air or water. As the fluid rises in temperature it expands and moves away from the heat source taking energy with it. The warm fluid is then replaced with colder fluid until the heat source and the fluid are the same temperature.
  • The amount of energy transferred is dependent upon the energy gradient
  • The rate of energy transferred depends upon surface area of contact and the fluid density. Water is a better convection material than air.
  • Convection can be minimized by trapping a warm fluid next to the body. This is how clothing works. It traps warm air in the clothing making it difficult to exchange warm air for cold. Non porous materials like plastic trashbags are effective for trapping warm air or water next to the body.
    
    
• Radiation - is the electromagnetic energy emitted by the body in the form of photons and waves.
  • Radiation heat loss is related to the amount of energy released within the body.
  • It is a small factor in the development of hypothermia.
  • The use of reflective body covering can minimize radiation losses. Reflection returns energy to the body.
    
    
• Evaporation - occurs when a fluid, such as water is heated to the point were it becomes a vapor. It requires a lot of energy to cause water to form steam. As the steam leaves the body it takes that energy with it, leaving the remaining water at a lower energy state.
  • Evaporation heat loss can be minimized by drying the body and hair thoroughly.
  • Capturing escaping heat and water by breathing through a thick porous material like a thick wool scarf.

Knowing how heat is lost can be helpful when assessing hypothermia risk. Frail elders will need to be scrupulously protected from conduction, convection and evaporative heat loss. Reducing drafts and layering clothing will minimize convection loss. Padding contact points and layering socks can reduce conduction losses. Keeping the body dry will reduce evaporative loss.

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