without reference, identify principles about hypothermia systems with at least 70 percent accuracy
TRANSCRIPT
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