Heat loss

You are providing general anaesthesia to a 47-year-old patient having an open hemicolectomy. You have been infusing all fluids through a fluid warmer but notice that the patient’s temperature has dropped to 35 °C. The patient will be losing MOST heat by which one of the following processes?

a) Conduction into the patient’s general surroundings

b) Convection with the room air

c) Radiation to the patient’s general surroundings

d) Evaporation from wound and skin

e) Respiratory losses from conduction, convection and evaporation

Answer: c

Explanation

Radiation is responsible for about 40% of the initial heat loss from an anaesthetised

patient. Convection into the operating room air accounts for another 30%. Evaporative

losses from the wound contribute another 15%, with respiratory losses and general

conduction only responsible for the small remaining heat loss. All of this may be

further complicated by factors such as infusing-room-temperature fluids or fridgetemperature

blood. The allocation of resources to combat peri-operative cooling should

be considered with these figures in mind.

Reference

NICE Guideline CG65. Online at www.nice.org.uk/Guidance/CG65 (Accessed 30

November 2009)