Quick Takeaways:
Four Mechanisms of Heat Loss –
1) Radiation – number one cause of heat loss in the OR
- transfer of body heat in the form of infrared radiant energy
2) Convection – loss of body heat to the ambient cooler air
3) Conduction – direct flow of body heat to a cooler supporting surface
4) Evaporation – warmed body moisture carries with it body heat upon evaporation
Heat loss upon induction of anesthesia
– immediate vasodilation of blood vessels in the periphery – skin, legs, tail – shunting or transfer of warmer blood from the core to the colder periphery – patient becomes a heat radiator
Three phases of hypothermia during general anesthesia –
- Phase 1
- rapid decrease in body temperature in the first hour (starts upon induction)
- due to redistribution of blood flow to the periphery
- ****81 Percent of Heat Loss That Will Occur****
- Phase 2
- slow decline of body temperature in the next 2 to 4 hours
- heat loss exceeds metabolic heat production by 20 to 40 percent
- Phase 3
- core temperature stability
- metabolic heat production equals heat loss
Preoperative Warming
– 81 Percent of heat loss occurs in the first hour after anesthetic induction
– ****Most Important Time to Start Active Warming and Heat Retention****
****Minimize delay between pre-op and intra-op warming. For every minute of delay the likelihood of a drop in core body temperature is increased by 5 percent****
Intraoperative Warming
– use active warming on as large a patient surface area as possible – implement measures to retain body heat
– minimize the time from pre-op to intra-op warming
Postoperative Warming
– continue active warming and heat retention until the patient is fully awake
TAKEAWAY – Start warming pre-op immediately upon anesthesia induction and minimize delay between pre-op and intra-op warming.
