Without reference, identify principles about Hypothermia Systems with at least 70 percent accuracy.

 Hypo/Hyperthermia Unit Primary Uses ◦ Maintain normal temperature in patients during and after surgery ◦ Decrease and stabilize the body temperature of febrile patients ◦ Elevate the body temperature of victims of accidental hypothermia

 Mechanisms of Heat Loss ◦ A healthy person resting at room temperature generates metabolic heat at a rate of approximately 70kcal/hr for a 154lb individual. Without heat loss from the environment, metabolic heat would cause body temperature to rise about 1 C/hr ◦ Body heat loss occurs by several mechanisms  Conductive heat loss  Heat loss to cooler objects in contact with the skin  Usually negligible (2%), even when a patient is recumbent (lying down)  Contacted surfaces are rapidly warmed to near body temperature  Most surfaces on which patients lie are poor thermal conductors

 Convective heat loss  Increases rapidly with wind velocity  Accounts for less than 20% of total heat loss at room temperature  When air temperature exceeds body temperature, the body gains heat energy  Radiational heat loss  Heat loss from transition of infrared radiation to cooler objects in the environment  Accounts for about 65% of the total heat loss at room temperature for an unclothed patient  Heat loss can be significantly reduced by covering exposed portions

 Temperature drops during surgery ◦ Ideally, the minimum core temperature during surgery should be 35 C  This may be too great a drop for very old, very young, or cardiac patients  Many researchers report much larger temperature drops-even down to 30 C-during surgery  Average Drops  0.3° C/hr for 20 year old patients  1.1° C/hr for 80 year old patients

◦ Temperature drops of 3-4 C, caused by the following mechanisms, are common during surgical procedures: ◦ Convective heat loss occurs because  Large amounts of the body's surface are exposed in the OR  Where humidity is low and temperatures are typically C  Hypothermia is common during pediatric surgery  The infant's relatively large body surface area, which increases heat loss to the atmosphere 2 Relatively small body mass for conserving heat

 Increased evaporative heat loss occurs:  When the patient breathes in dry anesthetic gasses  Volatile cleaning solutions are applied to the skin  Moist surgical wounds are exposed to the air  Infusing cold or room-temperature fluids (e.g. blood) contributes to heat loss  Anesthetic agents  Can affect the patient's thermoregulatory system promoting heat loss  Halothane causes blood vessels to enlarge reducing sensitivity to catecholamines, which promote heat gain

◦ Large temperature drops during surgery pose significant dangers  The risk of ventricular fibrillation increases and is especially great for cardiac patients  Patients who are already hypothermic are more susceptible to fibrillation caused by infusing cool fluids  Heat loss in the OR must be regained with increased circulatory and ventilatory effort in the postoperative period, when these functions in the patient may be compromised  Even a small temperature change will cause a large increase in a patient's oxygen uptake  Which is hazardous for cardiac patients  Shivering during this period may increase 02 uptake and CO2 production fivefold

 Methods of inducing temperature changes ◦ Invasive methods of raising body temperature  Most rapid  Usually reserved for severe hypothermia  These methods are not preferred  Require compromising the closed system of the body  Possibly enhancing the chance of infection or shock  Other methods of raising the body temperature may be slow. (hypothermia machines)

◦ External rewarming method  The core temperature may continue to drop  Factors reducing the long-term effectiveness of external rewarming in raising core temperature:  Vasodilatation  Inhibition of metabolism  Shivering

◦ Lowering body temperature  Clinicians may deliberately lower the temperatures of surgical, as well as febrile patients by:  Infusing cold water or using ice baths  Ice packs  Cold air ventilation o Sponge baths o Hypothermia machines

 Reducing body temperature slows metabolism by reducing the speed of biochemical reactions  When intentionally induced during cardiac surgery, or neurosurgery:  Hypothermia reduces the body's need for o Blood flow o Oxygen o Waste elimination  Thereby permitting greater tolerance of surgical procedures and reducing tissue injury