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Temperature Monitoring in Anesthesia

2016.07.01 / Friday

Temperature Monitoring in Anesthesia

By: David L.Reich

Temperature is a measure of the average kinetic energy of a collection of particles. Body temperature is maintained in a narrow range that permits biochemical enzymatic reactions necessary for homeostasis to occur. Although normal body temperature is often considered to be 37℃, this is an oversimplification. Body temperature actually fluctuates over the course of the day(with an early morning nadir and evening peak) and also varies based on age(lower in older individuals), gender(lower in males), activity level, and site at which it is measured. Mean rectal temperatures are typically in the range of 36.7 to 37.5℃, and mean axillary temperatures are 35.5 to 37 ℃.

 

Heat is measure of the energy transferred from particles of higher temperature to those of lower temperature. Heat gain can occur as a result of physiologic(e.g. exercise, shivering), pathologic(e.g. malignant hyperthermia, infection/inflammation), or iatrogenic(e.g. overwarming) processes. Heat is also transferred within the body owing to redistribution from the core to periphery and surface that occurs with the loss of regulatory mechanisms(e.g peripheral/ cutaneous vasoconstriction) during anesthesia. Heat loss from the body occurs in the typically cold operating room environment as a result of several mechanisms. Heat energy is transferred from higher to lower temperature surfaces by infrared radiation when there is no direct contact between the surfaces, and by conduction when there is direct contact between the surfaces. Convection contributes to heat loss when cool are currents absorb heat energy as they pass over warm body surfaces. Finally, evaporation of moisture from skin surfaces and surgically exposed body cavities results in loss of heat energy.

 

Maintenance of body temperature is the result of various physiologic sensors and effectors that appear to be integrated by the hypothalamus. These control mechanisms are impaired by anesthesia, both general and neuraxial, because of interruption of afferent, efferent, and central components of the thermoregulatory system. The resulting temperature decreases or increases can have adverse effects, may be beneficial, or may be signs of other underlying processes, making temperature monitoring an important component of perioperative care.

 

Temperature monitoring is also necessary to detect hyperthermia, which, similar to hypothermia, can have deleterious effects in some settings or may be an indicator of the presence of other disease processes. Hyperthermia is a relatively late sign of malignant hyperthermia, but temperature monitoring may help confirm the diagnosis and speed therapy. Although mild hyperthermia may improve leukocyte function in the setting of infection, it can have adverse affects in patients whose fever is related to or in addition to actual or potential neurologic injury. For this reason, temperature monitoring is important to prevent hyperthermia during rewarming after cardiopulmonary bypass. Similarly, hyperthermic patients with ischemis or hemorrhage, and refractory seizures may be cooled to prevent futher injury. However, such patients are generally cooled only to normothermic levels, as deliberate hypothermia has not been clearly proved to be beneficial in these settings.

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