الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 129 |  |  |
| | | from | 129 | | |
Abstract
Body temperature is normally tightly regulated, more so even than blood pressure or heart rate. The control system is complex and involves parallel positive- and negative-feedback systems that are so widely distributed that nearly every part of the autonomic nervous system participates to some extent . The processing of thermoregulatory information occurs in three phases: afferent thermal sensing, central regulation, and efferent responses . Most ascending thermal information traverses the spino-thalamic tracts in the anterior spinal cord to the hypothalamus . Temperature is regulated by central structures that compare integrated thermal inputs from the skin surface, neuraxis, and deep tissues with thresholds (triggering core temperatures) for each thermoregulatory response. The slope of response intensity versus core temperature defines the gain of a thermoregulatory response. The maximum intensity of the response is defined as when response intensity no longer increases with further deviation in core temperature.
Heat loss occurs primarily from the skin of a patient to the environment through several processes, including radiation, conduction and convection, and evaporation . Radiation is most significant and accounts for almost 60% of total heat loss , Heat from core body tissues is transported in blood to subcutaneous vessels, where heat is lost to the environment through radiation . Conduction refers to loss of kinetic energy from molecular motion in skin tissues to surrounding air while convection is heat transfer through a fluid medium such as air or water . Conduction and convection account for 15% of body heat loss . Roughly 22% of heat loss occurs by evaporation .
Body temperature is not homogeneous: deep thoracic, abdominal, and central nervous system (i.e., core) temperatures usually range from 2 to 4°C cooler than the arms and legs — and much of the skin surface is cooler yet. Core temperature monitoring (e.g., tympanic membrane, pulmonary artery, distal esophagus, and nasopharynx) is used to monitor intraoperative hypothermia, prevent overheating, and facilitate detection of malignant hyperthermia. Because these sites are not necessarily available or convenient, a variety of “near-core” sites are also used clinically. These include the mouth, axilla, bladder, rectum, and skin surface . Many types of thermometers are used but the most dependable ones are Mercury thermometer , Electronic thermometer and Infrared thermometer .
Hypothermia is defined as a core temperature <35°C and may be classified according to severity into : mild hypothermia (32.2°C to 35°C) , moderate hypothermia (28°C to 32.2°C) and sever hypothermia (<28°C) . serious consequences of hypothermia includes : cardiac arrhythmia and ischemia , reversible coagulopathy (platelet dysfunction) , altered mental status , impaired renal function , decrease drug metabolism , poor wound healing and increased incidence of infection .
There are three basic strategies for the prevention and treatment of perioperative hypothermia : minimizing redistribution of heat , cutaneous warming during anesthesia and internal warming . Minimizing redistribution of heat is achieved by : Prewarming and Pharmacologic Vasodilation . While cutaneous warming is achieved by : Passive Insulation , Active Cutaneous Heating , Circulating-water mattresses , Forced-air warming systems , Resistive Heating ( electric blankets ) , Radiant Warmers , Negative-pressure Warming and Hot-Water Containers . Meanwhile internal warming includes Fluid Warming and Airway Heating and Humidification .