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

Hypothermia System

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

Hypothermia System

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

Hypothermia System

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

Hypothermia System

◦ 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 18-19 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

Hypothermia System

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

Hypothermia System

◦ 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

Hypothermia System

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)

Hypothermia System

◦ 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

Hypothermia System

◦ 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

Hypothermia System

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

Hypothermia System