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Hypothermia & Anesthesia

Hypothermia & Anesthesia. Alex Roy, T4. Hypothermia. Core temperature <36°C Normally 37±0.2°C Maintained by compensatory mechanisms Skin & peripheral limbs maintain @ lower temps Mechanisms of heat loss Radiation (largest) Convection Evaporation Conduction. Hypothermia 2/2 Anesthesia.

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Hypothermia & Anesthesia

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  1. Hypothermia & Anesthesia Alex Roy, T4

  2. Hypothermia • Core temperature <36°C • Normally 37±0.2°C • Maintained by compensatory mechanisms • Skin & peripheral limbs maintain @ lower temps • Mechanisms of heat loss • Radiation (largest) • Convection • Evaporation • Conduction

  3. Hypothermia 2/2 Anesthesia • Interthreshold range increases from ±0.2 to ±4°C • Poikilothermia as pt temp approaches room temp • Anesthesia-induced vasodilation • Core warmth spreads to periphery • 0.5-1.5° temp loss in first 30 min after induction • Continues to drop slowly for 2-3 hrs and then stabilizes • Equal occurrence in spinal/epidural & general • MAC falls by 5-7%/°C • Environmental • Cold OR’s, cold IVF & blood products, prep exposure

  4. Physiologic Effects of Hypothermia • @ 33° • HTN, tachy, ↑ CO • ↑ O2 consumption • Hyperventilation • @ 28° • Hyperglycemia • Hypovolemia & hypotension • Cardiac – bradycardia, J-wave, v-fib, myocardial ischemia • Heme – ↑Hct, ↓platelets, O2-Hb curve shift (↓ O2 consumption) • Lactic acidosis • Prolonged drug metabolism

  5. Prevention • Recognition of pts most at risk • Infants, burn pts, trauma pts, & elderly • Wrap & cover • Airway warmth & humidity • Room temp • Warm beds/mattresses • Infrared heating lamps

  6. Treatment • 0.5-1.5°C/h gain is goal in most pts • Supplemental warming devices • “space blanket,” Bair Hugger, infrared lamps • Warm IVF’s & blood products • Hyperventilation key to prevent v-fib • Demerol to treat shivering • If below 27˚C, Heparin 300u/kg

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