Mechanism | Rate (kcal/h) | Description |
---|---|---|
Radiation | 10–50 | Transfer of heat energy via electromagnetic waves down a concentration gradient without direct contact according to Boltzmann’s equation:a Q = K(T1 – T2) |
 |  | Methods to reduce losses include: |
 |  |  • warming blankets |
 |  |  • increasing environmental temperature |
 |  |  • radiant heaters |
 |  |  • avoid unnecessary anesthesia |
Conduction | 16–30 | Transfer of energy between two solid objects in contact according to Fourier’s equation:b Q = KA dt/dx |
 |  | Methods to reduce losses: |
 |  |  • removal of wet clothing |
 |  |  • avoid prolonged contact with cold surfaces |
Convection | 10–20 | Transfer of heat energy during the mass movement of gas or liquid. |
Evaporation | 12–16 | Heat energy transferred during change of phase (water to gas): 58 kcal/g water evaporated from skin, respiratory tract, and viscera |
 |  | Methods to reduce losses for convection and evaporation: |
 |  |  • avoid prolonged surgery with an open abdomen |
 |  |  • warming blankets |