Hypothermia Flashcards by Adriana Comerford

inadvertent hypothermia happens to what percent of patients?

50%

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requires a nearly constant

internal body temperature

Homeothermic

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organism takes on the

temperature of the surrounding environment

Poikilothermia

[happens during anesthesia]

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central body temperature

abdomen, thorax, head

Core Temperature

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what controls temp in body?

hypothalamus via ANS

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amount of heat necessary to raise the temp of 1 kg of water from 14.5 to 15.5 C?

kilocalorie or 1000 calorie

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term for cooling?

thermolysis

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what 4 things effect thermolysis ?

conduction
evaporation
radiation
convection

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term for bodys ability to generate heat

thermogenesis

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4 things that effect thermogenesis

nonshivering
shivering
diet induced
basal metabolic rate

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thermoregulation maintains core body temp within what range?

0.2C of normal (37C)

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what 8 things can change body temp from normal?

Circadian rhythm
Exercise
Food intake
Infection
Thyroid function
Age
Anesthesia, sedatives, alcohol
Obesity

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explain thermoregulation differences with regards to infants and elderly?

intact in infants

impaired in elderly

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mechanism of action of normal thermoregulation?

T° info from thermally sensitive
cells travels warm (C fibers) & cold (A and D fibers) to
substantia gelatinosa of dorsal horn to the Hypothalamus

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the T ° regulating

center

hypothalamus

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unmyelinated, small, dull pain

c fibers

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thinly myelinated, sharp pain

A and D fibers

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can intense temperature be distinguished from pain?

no, they travel along same pathways

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First and most consistent response to hypothermia

Vasoconstriction

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Vasoconstriction Can decrease heat loss by

25%-50%

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why do we not want our patients to shiver?

can cause 2-5 fold increase in whole-body O2 consumption!! BIG problem

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can newborns and infants shiver?

Nope! increase metabolic heat production by nonshivering thermogenesis

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MOA of Non-shivering thermogenesis

NS fibers (beta receptors) innervate brown fat 
found in scapula, neck, back, viscera to stimulate lipolysis and heat release

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doubles the heat production in infants, but increases it only slightly in adults

Non-shivering thermogenesis

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when does bmr peak?

age 2

for each 1 degree F change, what does bmr change by?

most important insulator against heat loss

intact skin

Normothermia

36-37

Mild Hypothermia:

34ºC - 35.9ºC

Moderate Hypothermia

32ºC - 33.9ºC

Severe Hypothermia

< 32ºC

what does anesthesia vasodilation do?

Anesthesia-induced vasodilation allows core heat to flow peripherally.

where is most metabolic heat produced?

core compartment

Mechanisms of Heat Loss

radiation conduction convection evaporation

electromagnetic heat waves emanate from all surfaces; increased rate when temperatures higher than surrounding air

Radiation

Transfer of heat between two adjacent surfaces requires direct contact; molecule to molecule transfer of heat; warmer surface looses heat to cooler surface

Conduction

Loss of heat to air currents i.e. wind chill; normally hair on our body traps air in surface layer on the skin and counters forces

Convection

Loss of heat via water loss from the skin and mucus membranes

Evaporation

list mechanisms of heat loss in order from greatest to least

1. radiation 2. conduction 3. convection 4. evaporation

ALL anesthetics produce hypothermia—ALL - Why?

1. use of skeletal muscle relaxant (no shivering) 2. vasodilation 3. decrease BMR (20-40) 4. impaired non-shivering thermogenesis

hypothermia occurs in 3 phases, which produces most temp loss?

phase 1

describe phase 1 of temp decrease in OR

steep drop in temp (1-2 degrees) during first hour of procedure due to redistribution of core temp to periphery from vasodilation

gradual decline in next 2 to 3 hours (.5-1 degree/hour) due to continued heat loss to the environment exceeding heat production

phase 2

steady state; metabolic heat production matches heat loss

phase 3

what type of patients at greatest risk of inadvertent periop hypothermia?

pts receiving combined GA and RA [regional anesthes]

do epidural/spinals affect temp greatly?

They affect is but not as much as GA because you are only blocking responses in region of body, not entire body

warm response thresholds increases with anesth meaning

takes longer/higher temp to begin cooling off

cold response thresholds decrease with anesth meaning

has to get colder before techniques kick in

interthreshold range increases

10-20 fold

3 reasons Unwarmed patients become hypothermic with anesthesia

Open body cavities  Cold IV and irrigation fluids  Cold operating room

An operating room greater than ___ is required for | most adult patients to maintain normothermia

24C which is 75F | Not happening

why do infants have higher heat | loss from evaporation

Thinner skin and subcutaneous fat layer

5 Ways to prevent loss of heat in infants

1. ambient temp above 24C 2. overhead heater, fwa, heating blanket 3. kept wrapped and in incubator 4. head covered 5. warm fluids and skin prep

what 5 things cause elderly to be more prone to hypothermia?

1. slowed blood circulation 2. thin skin 3. decrease bmr 4. decrease lean muscle mass 5. blunted vasoconstrictor response

what is the treatment for post op shivering?

IV meperidine 25 mg clonidine 75 and supplemental O2

Consequences of hypothermia?

- increases blood loss - triples morbid cardiac outcomes - triples surgical wound infections - enhances drug effects

cardiac effects of hypothermia?

j wave dysrhythmias shift oxyhemaglobin curve to left increase PVR and blood viscosity

cardiac effects hypothermia in infants?

bradycardia (bad news bears)

common ekg changes in hypothermic pt?

junctional rhythm, prolonged pr interval, altered t wave, j wave

does hypothermia change emergence?

indeed, prolongs

Duration of vecuronium with 2C decrease in temp?

more than doubled

what % does MAC decrease for each 1C?

5 ways to prevent heat loss

1. blankets 2. forced warm air 3. heated inhaled gases 4. warming IV fluids 5. raise ambient temp

% heat loss from extremities

60%

% heat loss from Thorax/Abdomen

20%

% heat loss from Head and resp tract

10%

3 benefits of hypothermia?

1. protection against cerebral and spinal cord ischemia 2. malignant hyperthermia harder to trigger 3. MS

what types of surgery is hypothermia recommended?

carotid surgery, neurosurgery, TBI, any surgery where tissue ischemia can be anticipated

what 3 things does hypothermia do?

- decreases cerebral met rate 8% and blood flow 7% - decreases release excitatory enzymes - o2 consumption decreases 7%

best places to monitor temp?

``` Core Tº Nasopharyngeal, tympanic, PA catheter, esophageal -in the lower 1/3 of esophagus ```