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AP Summer > Hypothermia > Flashcards

Hypothermia Flashcards

1
Q

normal core body temperature is defined as:

A

37*C

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2
Q

Elderly have set-point ______ than normal

A

0.5*C Lower

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3
Q

Hypothermia- oral temp =

A

<36*C

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4
Q

Hyperthermia =
______ am
______ pm

A

> 37.2*C am

>37.7*C pm

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5
Q

what functions as the “control center” for temperature?

A

hypothalamus

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6
Q

what thermoregulatory mechanisms does the body exhibit at temps <37*C?

A

vasoconstriction followed by shivering

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7
Q

what thermoregulatory mechanisms does the body exhibit at temps >37*C

A

sweating followed by vasodilation

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8
Q

what happens to the threshold temperature for thermoregulatory responses under anesthesia?

A

widens range. Makes it harder for body to regulate

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9
Q

How are Mild, Moderate, Severe Hypothermia and DHCA defined?

A 
Mild = 34-36
Moderate = 30-40
Severe = <30
DHCA = 18*C
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10
Q

Where can core (trunk & head) body temp be measured?

A

Pulmonary Artery
Tympanic Membrane
Distal Esophagus
Nasopharynx

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11
Q

Name other places to measure temperature

A

Bladder
Rectum
Skin/Muscle

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12
Q

When would Bladder and rectal temperatures not be accurate?

A 
Bladder = poor kidney fxn, irrigation nearby
Rectal = "impaled on turd"
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13
Q

how do core and peripheral temps differ in their response to external influences?

A 
Core= varies little with environment
Peripheral = varies significantly over surface
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14
Q

how is temperature sensed?

A

afferent thermal sensing:
Cold= delta A fibers
Hot = C fibers

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15
Q

how does the body respond to heat?

A

sweating and active vasodilation

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16
Q

sweating can dissipate ___X the BMR in a dry, windy environment

A

10

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17
Q

when heated, what happens to the temperature gradient?

A

moves toward peripheral tissues

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18
Q

when cooled, what happens to the temperature gradient?

A

moves towards core

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19
Q

how does the body respond to cold? why can it be harmful?

A

vasoconstriction- moves circulation to core to preserve vital organs.
This can cut off flow to peripheral tissues and cause necrosis

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20
Q

what is the most effective thermoregulatory response?

A

behavior

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21
Q

shivering can have what effect on BMR?

A

increase 2-3x

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22
Q

what is non-shivering thermogenesis?

A

seen in infants - brown fat metabolism

increased SA to body ratio

23
Q

the majority of heat loss to the environment is due to?

A

radiation

24
Q

radiation is a function of what? This leaves what population particularly susceptible?

A

BSA

Children

25
Q

what is the second largest route of heat loss?

A

convection

26
Q

How does convection work and what affects its magnitude?

A

heat exchange from body to surrounding air/fluid

Magnitude effected by temperature gradient

27
Q

a bair hugger is an example of what form of heat exchange?

A

convection - per MM and manufacturer website.

28
Q

where are evaporative heat losses most common?

A

exposed visceral surfaces to environment and burns

29
Q

how can regional anesthesia effect thermoregulation?

A

affects afferent sensing, so hypothalamus isn’t sure what to do

30
Q

during anesthesia, where is the body heat redistributed?

A

to the periphery (resultant loss of core temp)

31
Q

most patients lose _____ *C in first hour

A

1-1.5*C

32
Q

what are the phases of cooling?

A
  1. Initial - redistribution (core->preiphery)
  2. core temp decrease in first hour (reduced vasoconstriction threshold)
  3. linear phase due to heat loss exceeding BMR
  4. Plateau when heat loss equals production
33
Q

T or F: Patients usually regain normal temperature by conclusion of surgery

A

False

34
Q

What effect does temperature have on wound infections and hospital stays?

A

Increases wound infection rate 3x

Increases hospital stay by 2 days

35
Q

thermoregulatory threshold for shivering is decreased _____ by inhalational anesthetics and nitrous-narcotic techniques

A

34.5*C

36
Q

thermoregulatory threshold for shivering is decreased _____ by proposal-nitrous techniques

A

33*C

37
Q

how do the elder compare to the normal population when looking at cooling and warming rates?

A

cool faster, warm slower

38
Q

what are 3 predictive factors of an increased risk for perioperative hypothermia?

A

old age
short height
low pre-op BP

39
Q

what two factors have a greater effect on hypothermia than the duration of surgery, ambient room temperature and percent body fat when using regional anesthesia?

A

high level of blockade

advanced age

40
Q

What are some possible consequences of hypothermia?

A 
-Poor would healing (Impaired immune fxn, 
decreased O2 to tissue, collagen production)
-increased mortality
-arrythmias
- ischemia and angina
- decreased drug metabolism
- reduced platelet fxn
- decreased activation of clotting
- blood loss
-prolonged PACU stay
- increased O2 consumption
41
Q

when is shivering more likely to occur?

A

when patient is rewarmed faster

42
Q

what effect does shivering have on O2 consumption?

A

increases

43
Q

what are some potential benefits to hypothermia?

A
  • (1-3*) = protection against cerebral ischemia
  • more profound = temp-dependent decrease in BMR and CMRO2
  • MAY improve outcome in septic ARDS
  • decreases MAC 5% per *C
44
Q

At what temperatures is brain injury likely vs neuroprotection?

A

37*C may cause brain injury

45
Q

what effect does temperature have on MAC requirements?

A

decreases MAC 5% per *C

colder patients require less anesthesia

46
Q

when would you want to induce deliberate hypothermia and why?

A

CPB for heart or brain surgery

  • improves tissue tolerance for ischemia
  • protects against ischemia
47
Q

in what instance would you not want to rewarm tissue?

A

Ischemic tissue should not be rewarmed
(ie tourniquet or AAA cross clamp)
-want to keep low BMR in ischemic areas

48
Q

when sampling temperature at multiple sites, which is the first to cool and rewarm?

A

esophageal

49
Q

temperature gradients are related to…..

A

differences in tissue blood flow

50
Q

what type of cooling is necessary to decrease O2 consumption for prolonged Circ. Arrest cases?

A

Uniform cooling

51
Q

what is used as an indicator of cerebral temperature?

A

nasopharyngeal temperature

52
Q

normothermic bypass patients showed an increased incidence of what adverse event?

A

stroke

53
Q

what are some methods to prevent hypothermia in the OR?

A
  • warm room, bed, fluids, inspired air

- use warming blankets and keep pt covered

AP Summer (24 decks)

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