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Principles 1 > Hypothermia > Flashcards

Hypothermia Flashcards

1
Q

inadvertent hypothermia happens to what percent of patients?

A

50%

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2
Q

requires a nearly constant

internal body temperature

A

Homeothermic

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3
Q

organism takes on the

temperature of the surrounding environment

A

Poikilothermia

[happens during anesthesia]

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4
Q

central body temperature

abdomen, thorax, head

A

Core Temperature

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5
Q

what controls temp in body?

A

hypothalamus via ANS

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6
Q

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

A

kilocalorie or 1000 calorie

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7
Q

term for cooling?

A

thermolysis

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8
Q

what 4 things effect thermolysis ?

A

conduction
evaporation
radiation
convection

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9
Q

term for bodys ability to generate heat

A

thermogenesis

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10
Q

4 things that effect thermogenesis

A

nonshivering
shivering
diet induced
basal metabolic rate

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11
Q

thermoregulation maintains core body temp within what range?

A

0.2C of normal (37C)

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12
Q

what 8 things can change body temp from normal?

A
  1. Circadian rhythm
  2. Exercise
  3. Food intake
  4. Infection
  5. Thyroid function
  6. Age
  7. Anesthesia, sedatives, alcohol
  8. Obesity
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13
Q

explain thermoregulation differences with regards to infants and elderly?

A

intact in infants

impaired in elderly

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14
Q

mechanism of action of normal thermoregulation?

A

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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15
Q

the T ° regulating

center

A

hypothalamus

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16
Q

unmyelinated, small, dull pain

A

c fibers

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17
Q

thinly myelinated, sharp pain

A

A and D fibers

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18
Q

can intense temperature be distinguished from pain?

A

no, they travel along same pathways

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19
Q

First and most consistent response to hypothermia

A

Vasoconstriction

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20
Q

Vasoconstriction Can decrease heat loss by

A

25%-50%

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21
Q

why do we not want our patients to shiver?

A

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

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22
Q

can newborns and infants shiver?

A

Nope! increase metabolic heat production by nonshivering thermogenesis

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23
Q

MOA of Non-shivering thermogenesis

A 
NS fibers (beta receptors) innervate brown fat 
found in scapula, neck, back, viscera to stimulate lipolysis and heat release
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24
Q

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

A

Non-shivering thermogenesis

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25
Q

when does bmr peak?

A

age 2

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26
Q

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

A

7%

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27
Q

most important insulator against heat loss

A

intact skin

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28
Q

Normothermia

A

36-37

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29
Q

Mild Hypothermia:

A

34ºC - 35.9ºC

30
Q

Moderate Hypothermia

A

32ºC - 33.9ºC

31
Q

Severe Hypothermia

A

< 32ºC

32
Q

what does anesthesia vasodilation do?

A

Anesthesia-induced vasodilation allows core heat to flow peripherally.

33
Q

where is most metabolic heat produced?

A

core compartment

34
Q

Mechanisms of Heat Loss

A

radiation
conduction
convection
evaporation

35
Q

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

A

Radiation

36
Q

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

A

Conduction

37
Q

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

A

Convection

38
Q

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

A

Evaporation

39
Q

list mechanisms of heat loss in order from greatest to least

A
  1. radiation
  2. conduction
  3. convection
  4. evaporation
40
Q

ALL anesthetics produce hypothermia—ALL - Why?

A
  1. use of skeletal muscle relaxant (no shivering)
  2. vasodilation
  3. decrease BMR (20-40)
  4. impaired non-shivering thermogenesis
41
Q

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

A

phase 1

42
Q

describe phase 1 of temp decrease in OR

A

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

43
Q

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

A

phase 2

44
Q

steady state; metabolic heat production matches heat loss

A

phase 3

45
Q

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

A

pts receiving combined GA and RA [regional anesthes]

46
Q

do epidural/spinals affect temp greatly?

A

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

47
Q

warm response thresholds increases with anesth meaning

A

takes longer/higher temp to begin cooling off

48
Q

cold response thresholds decrease with anesth meaning

A

has to get colder before techniques kick in

49
Q

interthreshold range increases

A

10-20 fold

50
Q

3 reasons Unwarmed patients become hypothermic with anesthesia

A

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

51
Q

An operating room greater than ___ is required for

most adult patients to maintain normothermia

A

24C which is 75F

Not happening

52
Q

why do infants have higher heat

loss from evaporation

A

Thinner skin and subcutaneous fat layer

53
Q

5 Ways to prevent loss of heat in infants

A
  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
54
Q

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

A
  1. slowed blood circulation
  2. thin skin
  3. decrease bmr
  4. decrease lean muscle mass
  5. blunted vasoconstrictor response
55
Q

what is the treatment for post op shivering?

A

IV meperidine 25 mg
clonidine 75
and supplemental O2

56
Q

Consequences of hypothermia?

A
  • increases blood loss
  • triples morbid cardiac outcomes
  • triples surgical wound infections
  • enhances drug effects
57
Q

cardiac effects of hypothermia?

A

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

58
Q

cardiac effects hypothermia in infants?

A

bradycardia (bad news bears)

59
Q

common ekg changes in hypothermic pt?

A

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

60
Q

does hypothermia change emergence?

A

indeed, prolongs

61
Q

Duration of vecuronium with 2C decrease in temp?

A

more than doubled

62
Q

what % does MAC decrease for each 1C?

A

5%

63
Q

5 ways to prevent heat loss

A
  1. blankets
  2. forced warm air
  3. heated inhaled gases
  4. warming IV fluids
  5. raise ambient temp
64
Q

% heat loss from extremities

A

60%

65
Q

% heat loss from Thorax/Abdomen

A

20%

66
Q

% heat loss from Head and resp tract

A

10%

67
Q

3 benefits of hypothermia?

A
  1. protection against cerebral and spinal cord ischemia
  2. malignant hyperthermia harder to trigger
  3. MS
68
Q

what types of surgery is hypothermia recommended?

A

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

69
Q

what 3 things does hypothermia do?

A
  • decreases cerebral met rate 8% and blood flow 7%
  • decreases release excitatory enzymes
  • o2 consumption decreases 7%
70
Q

best places to monitor temp?

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

Principles 1 (12 decks)

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