Perioperative patient temperature changes are a “hot” topic now. Numerous studies over the past decade have shown a relationship between patient hypothermia and surgical wound infection and length of hospital stay in addition to the things related to patient temperature that have been long known, such as shivering, cardiovascular stress, coagulopathies, and patient satisfaction. The importance of regulation of room temperature for patient normothermia instead of staff comfort has been recognized. Some medical insurance companies audit perioperative patient temperature as an indicator of appropriate care for reimbursement.
Several methods are used to keep patients normothermic in the perioperative period. Some work much better than others. Some provide active warming, but some are passive in nature. We will talk about the different kinds of patient heat loss, as well as the different methods and the efficacy of each.
Methods of Perioperative Heat Loss
Intuitively, it is not hard to understand why patients get cold perioperatively. You are placed in a cold room, told to take off your clothes, and put on a flimsy short-sleeve gown that is open in the back. You may or may not have a blanket. Then you are given intravenous (IV) fluid that is room temperature. You are wheeled down a cold, drafty hallway into a cold room and placed on a cold bed. You are given drugs that negatively alter your body’s thermoregulation. Then after you are unconscious, you are uncovered totally, positioned, washed in room temperature solution, and given more room temperature IV fluid. By the time you are covered up in surgical drapes, your temperature has dropped at least 1°C. The length and location of the operation will affect the degree of hypothermia, as well as the amount of IV fluid. You will lose 0.25°C of body temperature for every liter of room temperature IV fluid given. So it is easily understood why you get cold. But what are the methods of heat loss, speaking in terms of physics?
The four main methods of heat loss in an anesthetized patient are radiation, conduction, convection, and evaporation. You may not remember the differences in these, so we will go over each one.
For this form of heat loss, think of heat as light (they both are energy, of course). In this example, the patient emits heat by radiation just like a light bulb emits light into the room. The colder the environment, the more heat is radiated away from the patient. This is actually the main way a patient loses heat.
This is when heat energy flows from one molecule to another or one object to another. Contact is needed ...