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NA 1 > Thermoregulation - Exam 3 > Flashcards

Thermoregulation - Exam 3 Flashcards

1
Q

4 ways body loses heat:

A

-RADIATION (#1 in and out of OR)
-convection
-conduction
-evaporation

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2
Q

What is normal body temp roughly?

A

37*C

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3
Q

3 phases of thermoregulation:

A

afferent sensing
central regulation
efferent response

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4
Q

T/F thermoregulation works via negative feedback

A

false,
BOTH + and - feedback

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5
Q

Warm receptors increase firing rates as temperature _.

A

increases
-RECEPTORS fire, not EFFECTORS

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6
Q

Cold signals travel via _ fibers and warm signals travel via _ fibers

A

cold - A delta
warm - UNmyelinated C

-sometimes an overlap

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7
Q

Temperature sensors appear to be a class of _ _ _ protein receptors

A

transient receptor potential (TRP)

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8
Q

ASCending thermal info travels via the _ tract which is in the _ spinal cord

A

spinothalamic
anterior

-not in any specific spinal tract, involves many

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9
Q

T/F Complete destruction of the hypothalamus would ablate thermal RESPONSE

A

false; the ANTERIOR SC, not hypothal
- adaptive measures exist to regulate
ex) high SC transection can still provide thermoreg sometimes

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10
Q

T/F C fibers sometimes struggle to distinguish between intense cold and dull pain

A

False
-intense HEAT and SHARP pain

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11
Q

Temperature is regulated by central structures (hypothal) receiving integrated thermal inputs from _ , _, and _ and comparing them with _ temperatures for each thermoreg response

A

skin surface
neuraxis
deep tissue
THRESHOLD TEMPS

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12
Q

Some thermal input/output is “preprocessed” in the _ _

A

spinal cord
-preset responses not needed to be processed by hypothal

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13
Q

Gain =

A

intensity
-seen as a slope; end of slope = max intensity

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14
Q

Body’s normal determination of absolute temp threshold seems to be mediated by:

A

-NE
-dopamine
-5-hydroxytryptamine (nerd for “SEROTONIN” or “5-HT”)
-ACh
-Prostaglandin E
-neuropeptides

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15
Q

Pt related factors that affect temp threshold:

A

-circadian rhythm
-monthly cycle (0.5*C change in women)
-food intake
-infection
-hypo/hyperthyroidism
-natural adaptations
-drugs/alcohol/nicotine/etc

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16
Q

Skin temp contributes _ % to control of each thermoreg defense

A

20%

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17
Q

Control of AUTONOMIC responses is ~ _ % determined by thermal input from core structures

A

80%

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18
Q

Most of input controlling BEHAVIORAL responses is derived from the _ _

A

skin surface

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19
Q

The interthreshold range is the range of temperatures in which core temps aren’t triggering an _ response

A

autonomic
-varies by few tenths of degree centigrade

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20
Q

T/ F The upper limit of the interthreshold range is the sweating threshold and the shiver threshold on the low end

A

FALSE!
sweating and vasoconstriction

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21
Q

The relationship between skin temp and core temp triggering vasoconstriction and sweating is _

A

linear

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22
Q

During the menstrual cycle, the follicular phase (pre-ovulation) has _ temperature than the luteal phase (post-ovulation)

A

lower

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23
Q

Even during the follicular phase, a woman’s sweating and vasoconstriction thresholds are -*C higher than in men

A

0.3-0.5*C higher thresholds than men (and even more when in luteal phase)
-this means men sweat and vasoconstrict at lower temps than women do

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24
Q

Who sucks at central thermoreg control more, old ppl or premature infants?

A

old ppl

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25
Q

The body likes the path of least metabolic resistance, which happens first, shivering or vasconstriction?

A

vasoconstriction
-more energy efficient

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26
Q

The interthreshold range in humans is usually only _ *C

A

0.2*C

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27
Q

3 things can happen when core temp is below interthreshold range:

A

-vasoconstriction
-nonshivering thermogenesis
-shivering

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28
Q

2 things can happen when core temp is above interthreshold range:

A

-vasodilation
-sweating

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29
Q

_ determine the ambient temp range that the body will tolerate while keeping a normal core temp

A

Effectors

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30
Q

T/F If an effector is inhibited(like shivering after a NMBD), the tolerable range will decrease and so will total body temp

A

false,
compensatory mechs in place to correct this until they they too fail

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31
Q

QUANTITATIVELY, which type of effector temp regulation mechanism is most important?

A

Behavioral
-putting on more clothes, staying away from cold/heat/etc

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32
Q

T/F Decreased muscle mass, NM disease, and taking muscle relaxants increase shivering and lower the minimum tolerable ambient temp.

A

False
MR drugs and these things INHIBIT shivering and INCREASE minimum tolerable ambient temp

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33
Q

Anticholinergics inhibit the _ ganglionic cholinergic nerves responsible for sweating and _ the maximum tolerable temp

A

postganglionic
decrease
-ex) atropine admin will inhibit sweating

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34
Q

Which effector is the most consistently used autonomic mechanism?

A

cutaneous vasoconstriction

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35
Q

Vasoconstriction reduces which 2 forms of metabolic heat loss from skin?

A

convection
radiation

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36
Q

Total digital skin blood flow is divided into _ (capillary) and _ (AV shunt)

A

nutritional
thermoregulatory

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37
Q

T/F AV shunts are anatomically and functionally similar as capillaries and vasoconstrictions can cause peripheral issues

A

False
-theyre structurally/functionally different and so nutrient-dense blood is not constricted away from periphery

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38
Q

Shunts are about _ mcm in diameter and capillaries are about _mcm

A

100mcm
10mcm
-therefore shunts can carry 10k x more blood than capillaries of equal length

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39
Q

AV shunts are all or nothing and have _ gains over _ changes in core temp

A

high
small

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40
Q

Thermoregulatory AV shunts ability to constrict is mediated by local _ adrenergic _ nerves and minimally by circulating _

A

alpha adrenergic sympathetic n
catecholamines

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41
Q

About _% of cardiac output traverses AV shunts and vasoconstriction of these can cause a increase MAP by about _mmHg

A

10%
15mmHg

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42
Q

ALL GA markedly impair normal ___________ thermoreg control

A

Autonomic

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43
Q

Anesthetics cause warm thresholds to _________ slightly and cold response thresholds to drastically ________.

A

increase
reduce

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44
Q

Anesthetics cause the interthreshold range to increase from 0.3C to about ___ to ___ deg C

A

2 to 4 deg C
-from increased sweating and reduced vasoconstriction thresholds
-pt is poikilothermic in this range

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45
Q

T/F: Anesthesia decreases all thermoreg responses, gain, and maximum intensity.

A

False, some responses remain normal

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46
Q

**BIG MONEY*
For Anesthetics like Desflurane, alfentanyl, Dexmedetomidine, and propofol, the sweating threshold will slightly _______ while markedly + synchronously _______ the vasoconstriction and shivering thresholds.

A

increase
decrease

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47
Q

When a pt receives anesthetics and their interthreshold range increases from ____ deg C to ___ to ___ deg C, they are considered _________ and will not trigger a tresponse

A

0.2deg C to 2-4deg
poikilothermic

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48
Q

N20 decreases vasoconstriction and shivering thresholds ____than equipotent concentrations of volatile anesthetics.

A

less

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49
Q

T/F: Midazolam severly impairs thermoreg control.

A

false, minimally

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50
Q

Painful stim slightly ______ vasoconstriction thresholds, so thresholds are _________ with the use of local or regional anesthetics

A

increases
decreased

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51
Q

T/F: 3 Cold responses in anesthetized adults include: vasoconstriction, nonshivering thermogenesis, and shiver.

A

False, non-shiver thermogen doesn’t occur w/ adults under GA

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52
Q

T/F: Nonshiver thermogen increases metabolic rate in infants after propofol admin.

A

False, no bueno, babies rely on this a lot

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53
Q

Shiver threshold is about ___ deg C less than the vasoconstriction threshold and _____ occurs in surgical doses of GA.

A

1degC
rarely

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54
Q

The best preserved thermoreg defense during GA is _____

A

sweating

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55
Q

Under GA, sweat threshold is slightly _____ and gain and max intensity are _____

A

increased
normal

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56
Q

The efficacy of which 2 thermoreg defenses are diminished with GA?

A

vasoconstriction & shiver

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57
Q

Heat transfer via radiation is proportional to….

A

difference of the 4th power of the absolute temp difference between surfaces.
Think the Sun or Lights and your skin.

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58
Q

Conductive heat loss is proportional to….

A

temp difference between 2 adjacent surfaces and the strength of the thermal insulation seperating them. Think heat transferring through solids
-not common in OR bc of foam pads insulating

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59
Q

Convective heat loss increases substantially in ORs that provide ______ Flow

A

Laminar

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60
Q

Evaporative heat loss from skin surfaces is < ___% of metabolic heat production in adults in the absence of sweating from GA

A

<10%

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61
Q

Population most at-risk from evaporative heat loss =

A

-premies (lose 1/5 of metabolic heat production via transcutaneous evap)
-large surgical wounds
-infants

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62
Q

-Hypothalamus
-other parts of brain
-spinal cord
-deep abdominal and thoracic tissue
-skin
EACH contribute to _% of total thermal input

A

20%

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63
Q

Sustained shiver increases metabolic heat production by -% unlike exercise which is 500%

A

50-100%
-shivering isn’t very efficient

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64
Q

Tremor associated with normal shivering is less than or equal to _Hz and has unsynchronized muscle activity that waxes and wanes around - cycles per minute

A

250Hz
4-8 cycles/min

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65
Q

Sweating is efficient and dissipates about _ kcal/g of evaporated sweat

A

0.58kcal/g

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66
Q

Untrained people can sweat up to _L/hour

A

1L/hr – fluid loss!
-athletes can sweat 2L/hr

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67
Q

During extreme heat stress, the 1st mm of skin can have blood flow equaling _L/min which is normal whole resting cardiac ouput

A

7.5L/min
-vasodilation

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68
Q

Anesthetics change interthreshold range from 0.3C (I saw 0.2C somewhere else) to -*C

A

2-4*C
-20 fold increase in range

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69
Q

Most anesthetics except meperidine and nefopam cause vasoconstriction and shiver thresholds to _ while maintaining their _*C difference

A

decrease
1*C

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70
Q

VA with N2O or fentanyl _ the vasoconstriction threshold by 2-4C from _C

A

decrease
37*C

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71
Q

The vasoconstriction threshold is about _*C less in 60-80 year olds than in 30-50 year olds.

A

1*C
-elderly pts get more cold before their body tries compensating

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72
Q

The shiver threshold is usually _ *C less than the _ threshold

A

1*C
vasoconstrictionq

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73
Q

Radiation is proportional to (equals)

A

difference of the 4th power of the absolute temperature differences between surfaces

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74
Q

Convection is proportional to (equals)

A

square root of air speed

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75
Q

Air speed in OR is usually

A

20cm/sec

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76
Q

When not sweating, evaporative heat loss from the skin surface is < _ % of metabolic heat production

A

<10%
-when not sweating, heat loss from evap is not significant; radiation and convection are significant

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77
Q

Anesthetics decrease the metabolic rate by -%

A

20-30%

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78
Q

1st hr of anesthesia can drop core temp by -*C

A

0.5-1.5*C

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79
Q

Normally core temp represents only _% of body mass (head and trunk) and the remaining mass is about -*C cooler than the core temp

A

50%
2-4*C cooler elsewhere in body

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80
Q

After initial redistribution hypothermia, core temp decreases slowly and linearly for _-_hours

A

2-4 hrs

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81
Q

After _-_hrs of anesthesia, core temp reaches a plateau and stays pretty constant

A

3-4hr

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82
Q

Core temp plateauing after 3-4hr of anesthesia is due to _ vasoconstriction which is triggered by core temperatures of -*C

A

peripheral
33-35*C

-could also just be from heat production = heat loss and pt reaching steady state

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83
Q

Core temp dropping after anesthesia is 81% due to _

A

redistribution

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84
Q

Epidural and spinal blocks both cause _ vasoconstriction and shiver thresholds by _*C _ the level of the block.

A

decreased
0.6*C
ABOVE

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85
Q

Even short acting LA like 2-chloroprocaine with a half life of _ sec can impair thermoregulation

A

20 sec

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86
Q

Leg skin temps of _*C are needed to prevent cold response in an unanesthetized pt similarly to regional blocks

A

38*C

87
Q

After epidural anesthesia, the gain for thermoreg defenses are decreased _ fold

A

3.7

88
Q

Core temp usually decreases 0.5-1*C after _

A

induction

89
Q

Regional and GA vasoconstriction thresholds are _*C less than GA thresholds alone

A

1*C
-adding regional to GA makes cold response thresholds even lower

90
Q

The lower body contributes to _% of thermoreg control

A

10%

91
Q

Antishiver drugs and doses DURING anesthesia:

A

-Meperidine 25mg IV or epidural
-Clonidine 75mcg IV
-Precedex
-Katenserin 10mg IV
-Mag sulfate 30mg/kg IV

92
Q

Hypothermia of -C can be protective for cerebral ischemia and core temps of _C are sometimes used in neuro cases

A

1-3C
34C

93
Q

Coag labs are processed at _*C so it is difficult to assess coag changes from hypothermia

A

37*C

94
Q

Just a _*C drop in core temp can increase both blood loss and the risk of needing transfusions by _%

A

1*C
20%

95
Q

The DOA of Vec is doubled when core temps are _*C less than normal

A

2C
-atracurium is less dependent but a 3C drop increases DOA by 60%
-this is due to pharmacoKINETIC effect, not pharmacodynamic

96
Q

Even without MR, twitch responses are decreased by _ -_% when pt is hypothermic

A

10-15%

97
Q

Neostigmine efficacy is _ during hypothermia but onset is _% longer than normal

A

unchanged
20%

98
Q

3*C hypothermia causes a _% increase of plasma concentration of propofol

A

30%

99
Q

The MAC of volatile anesthetics is _% less per _ *C drop from normothermia and this is due to hypothermia influencing the pharmaco- _ effects

A

5%,
1*C
pharmacodynamic

100
Q

Core temps < _*C do not require anesthesia to prevent movement response from incision

A

20*C

101
Q

Hypothermia increases infection risk and duration of hospitalization by _%

A

20%

102
Q

_% of pts experience post anesthetic tremor/shiver

A

40%

103
Q

Postop shivering increases O2 consumption by _%

A

100%

104
Q

Postop shiver has a _ pattern like normal shivering with wax/wane 4-8cycles/min but also has a _ pattern than have 5-7Hz burst like clonus

A

tonic
phasic

105
Q

Cutaneous warming is not very effective is pt core temp is < _*C

A

< 35*C

106
Q

POSTOP(not intraop) shiver treatment and doses:

A

-Clonidine 75mcg Iv
-Ketanserin 10mg IV
-Tramadol
-Physostigmine 0.04mg/kg IV
-Nefopam 0.15mg/ kg
-Precedex
-Mag sulfate 30mg/kg IV

-Difference from intraop: no meperidine, added tramadol, physostigmine, and nefopam

107
Q

T/F Narcan reverses antishiver effects of meperidine

A

false
-only in large doses >5mg/kg/min

108
Q

Normally, _% of metabolic heat loss is thru skin surface, with anesthesia, more is lost from _ and from cold _

A

90%
incisions
cold IV fluid

109
Q

Prewarming for as little as _ min can prevent redistribution hypothermia

A

30min

110
Q

T/F Respiratory tract has a significant role in heat loss

A

false, <10%

111
Q

Who benefits from cutaneous skin warming more, kids or adults?

A

kids
10x more effective

112
Q

1 unit of refrigerated blood or 1L of ROOM TEMP crystalloid can drop mean body temp by _*C

A

0.25*C
-this is bc 1 unit of COLD blood is about half of volume of 1L of ROOM TEMP crystalloid

113
Q

COLD IV fluid can drop mean body temp by _ C and ROOM TEMP IV fluid can drop it by _C

A

0.5C cold
0.25C cold
-remember 1 unit of blood can drop it by 0.25*C too bc it is HALF volume of 1L crystalloids

114
Q

Room temp required to maintain normothermia is >_C in adults and >_C in infants

A

> 23C
26C

115
Q

Single layer of insulation reduces heat loss by _%.

A

30%
-adding 3 layers = 50%
-diminishing return!

116
Q

90% of metabolic heat loss is thru skin so only _ _ can transfer enough heat to prevent hypothermia

A

cutaneous warming

117
Q

T/F Burns happen when water temp is >40*C

A

false
they can happen before that

118
Q

When cutaneous heat loss is eliminated, metabolic heat production increases mean body temp by _*C / hr

A

1*C

119
Q

Target temp for mild therapeutic hypothermia is a core temp between:

A

32-34*C

120
Q

T/F Forced air COOLING is efficient

A

false
-takes 2.5 hr to cool pts to 35*C

121
Q

_ cooling is the most effective way to decrease temperature and does so at a rate of _*C/hour

A

Endovascular
4*C/hr
-invasive, requires a heat exchange catheter in the IVC via a fem line

122
Q

_ and meperidine synergistically reduce the shiver threshold to _ *C with minimal sedation and respiratory toxicity

A

Buspirone
34*C

123
Q

Deep hypothermia (28C) was used for CABGs in past but they now perform them at _C or normothermia

A

33*C

124
Q

Deep hypothermia of _*C is used for intentional circulatory arrest

A

18*C

125
Q

Whole body metabolic rate decreases with hypothermia at a rate of _%/C and reaches a 50% metabolic rate at _C

A

8%/C drop
50% rate by 28C

126
Q

Cerebral function is maintained until core temp reaches _C and loss of consciousness occurs at _C

A

33C
28C
-SSEPs decrease at 33*C

127
Q

Primitive reflexes(gag, pupil, spinal reflexes) remain intact until core temp reaches_*C

A

25*C

128
Q

Nerve conduction _ but peripheral muscle tone _ causing tension and myoclonus at core temps of _*C

A

decreases
increases
26*C

129
Q

SA pacing and ventricular irritability occur when core temps <_C. Fibrillations occur between -C and defib will _ work

A

<28C
25-30C
defib will NOT work!

130
Q

Temps < _ *C will decrease respiratory strength but CO2 ventilatory drive will not change

A

<33*c

131
Q

For each 1*C drop in core temp, pH of blood _ by 0.0017 units

A

increases
-colder pts will be more ALKALOTIC!!

132
Q

Hypothermia causes a _ shift in the oxyhemoglobin association curve but _ metabolic rate

A

LEFT shift
decreases

133
Q

What is pH stat?

A

Body’s attempt to regulate blood pH at 7.4

134
Q

During MH, circulating catecholamine concentration is 20x the average, and the resulting vasoconstriction compromises _ heat loss mechanisms

A

efferent

135
Q

When pregnant pt is hyperthermic with an epidural and laboring for > _hrs, what happens next?

A

8hrs
-hyperthermia is taken as a true fever, infant is presumed septic and mom is given abx
-epidural analgesia is associated with intrapartum fever but only in the presence of placental inflammation

136
Q

WHY do we not need to monitor temp if case is <30 mins?

A

bc core temp changes are difficult to interpret at this point

137
Q

When must temperature monitoring occur?

A

-if pt receives anesthesia for >30 mins

-if CASE > 1hr long

-if pt is a kid!

-if pt is having surgery with neuraxial anesthesia

-if expecting/intending for temperature changes for case OR if there are notable signs of change during the case

138
Q

80% of thermal input is derived from _ _

A

core temp

139
Q

GA decreases the hypothermia response thresholds from _C to -C

A

37C
33-35C

140
Q

Keep the pts core temp _*C unless otherwise indicated for the case

A

36*C

141
Q

Clonidine synchronously _ cold response thresholds and slightly _ sweat thresholds

A

decrease
increase

142
Q

Which VA causes AV shunt vasoconstriction gain to decrease threefold while preserving its max intensity?

A

Desflurane

143
Q

T/F Vasoconstriction usually prevents additional hypothermia so even unwarmed pts rarely are cold enough to shiver

A

true
-during anesthesia tho pts are not able to increase heat PRODUCTION to outweigh hypothermia

144
Q

Gain and max intensity of shiver stays the same with admin of which 2 drugs:

A

meperidine and alfentanil

145
Q

Gain is _ with N2O use and max intensity is _

A

unchanged
decreased

146
Q

2 reasons for hypothermia:

A

anesthetic impaired thermoreg and exposure to cold OR environment

147
Q

VA cause vasodilation via _ peripheral action and _ tonic thermoreg vasoconstriction, causing AV shunt dilation

A

direct
inhibit

148
Q

T/F Body heat is evenly distributed

A

false

149
Q

Core to peripheral tissue temp gradient is normally preserved by _ _ _.

A

tonic thermoreg vasoconstriction
-blunted by GA

150
Q

Anesthetic induced vasodilation warms arms and legs at the expense of the _

A

core
-extent of redistribution of heat depends on core-peripheral temp gradient before induction

151
Q

T/F A core temp plateau caused by vasoconstriction is NOT considered steady state bc heat is still lost via periphery and they get colder while core temp is preserved

A

true

152
Q

Threshold decreases seen in regional anesthesia are NOT from redistribution but from altered _ control from altered AFFerent input from _

A

central
legs
-redistribution still happen tho

153
Q

The skin temp on the legs is dependent on _ cold signals

A

tonic

154
Q

Regional anesthesia blocks _ thermal input from blocked regions and this is usually _ information, causing brain to assume legs are _.

A

all
cold
warm

-awake pts will know they are not warm, but will “feel” warm

155
Q

T/F IV LA causes decreased thresholds

A

false

156
Q

Normally, leg temps of _*C can blunt cold responses but _ anesthesia can mimic this

A

38*C
regional

157
Q

Regional anesthesia _ gain and max intensity of shiver and vasoconstriction by half of what is normal

A

reduces
-drugs usually given with regional, old age, and comorbidities add to this

158
Q

T/F core hypothermia during regional anesthesia may not trigger a perception of cold

A

true
-there is a REAL increase in skin temp even when core temp is low so pt will feel warm but still be shivering
-unmonitored temp changes with regional can be dangerous!

159
Q

T/F Regional anesthesia produces core-peripheral redistribution and reaches plateau just the same as GA.

A

False!
-there is no plateau with regional bc the block prevents vasoconstriction in the legs and core temp is further reduced from vasodilation

160
Q

Will a pt receiving GA and regional reach a plateau core temp?

A

no
-v important to measure core temp!

161
Q

T/F Temp of injected LA can influence incidence of shivering

A

false

162
Q

Sometimes lwo intensity tremors happen with regional that aren’t associated with temperature but rather with _

A

pain

163
Q

Protective action of hypothermia is associated with decreased release of excitatory _ _

A

amino acids

164
Q

T/F Therapeutic hypothermia is best used in pts after ROSC from in-hospital cardiac arrest, neurosurgery, and for asphyxiated neonates

A

False!
-All are true but using post-arrest requires that pt experienced arrest OUT of hospital

165
Q

T/F Allowing pts at risk for MH to be slightly hypothermic increases their risk of developing MH

A

false
-it is helpful in preventing and reducing effects of MH if it is triggered
-cutaneous warming preop should be avoided - gets them closer to the edge

166
Q

Cold causing a defect in platelet function is related to _ temperature

A

local
-not core

167
Q

Wound temperature is determined by _ temperature

A

core
-distinctly higher in normothermia

168
Q

Cold _ impacts the enzymes of the clotting cascade, and normal labs are hard to reflect this change bc they are processed usually at 37*C

A

directly

169
Q

Hypothermia influences immune function by:

A

-impairing O2 delivery to tissues
-preventing protectives fever mechanism
-urinary nitrogen remains elevated for days postop (indicates poor wound healing)

-body is less resistant to E.Coli and Staph

170
Q

Postop thermal discomfort is distressing and can _ BP, HR, and plasma catecholamine concentration

A

increase

171
Q

Most important consequence of mild hypothermia:

A

3x increase in morbid myocardial outcomes

172
Q

T/F Myocardial ischemia is associated with shivering and increased O2 demand

A

false

173
Q

Postop tremor/shivering can be from several causes:

A

-uninhibited spinal reflexes
-decreased sympathetic activity
-pyrogen release
-adrenal suppression
-respiratory alkalosis
-intraoperative hypothermia

-more common in those of young age and low core temp

174
Q

Postop shiver is different than normal shiver bc:

A

-although it has tonic tremor (4-8 cycle/min wax and wane), it also has a clonus pattern hat is similar to spinal cord responses (both being thermoregulatory)

175
Q

Clonus pattern seen in postop shivering is associated with administration of _ _ and is likely from anesthetic-induced disinhibition of the normal _ control of spinal reflexes

A

volatile anesthetics
descending

176
Q

Non-thermoreg tremor similar to clonus is seen in laboring pts and is likely from _

A

pain

177
Q

Will cutaneous warming for postop shiver work?

A

only a little if core temp is at or above 35*C

178
Q

Clonidine and precedex are thought to work on the _ thermoreg system due to the fact that they both reduce vasoconstriction and shivering thresholds

A

central

179
Q

Which is better at preventing/treating postop shiver, alfentanil or meperidine?

A

meperidine
-likely related to agonist activity at central alpha adrenoreceptor

180
Q

Intraop hypothermia can be reduced by minimizing risks for cutaneous heat loss which happens via:

A

-cold OR environment
-evaporation from incision
-cold IV fluids

181
Q

Mean body temp decreases when heat loss to environment is > :

A

metabolic heat production

182
Q

_ tone alters intercompartmental heat transfer and _ tone and AV shunt status is modulated by anesthetics, both affecting speed of peripherally applied heat reaches the core

A

Vasomotor tone
Arteriolar tone

183
Q

In PACU 2 pts are cold and have Bair huggers on. Which one warms quicker, the one who received only GA or the one who only had regional which is still lingering?

A

Regional
-this is bc once GA wears off and vasodilation goes away pt will experience unopposed vasoconstriction making it harder to warm the core, whereas regional pt will still have vasodilation from the block, allowing warm peripheral blood to flow back to the core and warm up quicker

184
Q

Core warming is slower after GA postop bc vasoconstriction constrains up to _kcal in peripheral tissue

A

30kcal

185
Q

Applied warming is most effective when pt is vasoconstricted or vasodilated?

A

vasodilated
-better to warm INTRAOP not POSTOP (easier to achieve and prevents complications)
-even better to warm in preop

186
Q

Most important component of peripheral heat compartment:

A

legs

187
Q

T/F Prewarming increases core temp significantly

A

false
-increases heat CONTENT of peripheral compartment, this inhibits the need for tonic thermoreg vasoconstriction and causes less redistribution hypothermia (heat flows only DOWN temp gradient)

188
Q

Heat loss via resp tract is minimal but occurs via heating and humidifying via the _ phase of breathing

A

inspiratory
-heat loss is NOT thru expiratory phase
-humidification costs the most heat of the two factors

189
Q

Who benefits more from airway heating/humidification waming methods, kids or adults?

A

kids
-cutaneous warming is better than airway heating and this applies to everybody but kids benefit 10x more than adults
-humidifiers include Hygroscopicc condenser and “Artificial noses”

190
Q

Why is it impossible to heat ppl with heated IV fluid?

A

Can’t really be higher temp than body
-room temp and cold fluids chill body very easily tho, use fluid warmer if giving a lot of fluids!

191
Q

Most critical factor influencing heat loss:

A

OR room temp
-determines rate of metabolic heat loss

192
Q

EASIEST way to decrease cutaneous heat loss:

A

passive insulation
-1 layer = 30% less heat loss, diminishing return with more layers tho (3 layers only 50% decrease)

193
Q

Which is more important, amount of skin covered or location of skin being covered?

A

amount covered
-covering adults head does not do much but it does for babies bc their heads make up large part of body surface area

194
Q

Why are water circulating pads not great for warming?

A

-would be placed on back if pt is having surgery and back is already insulated by foam on table
-could burn pt if placed on back due to decreased capillary flow from pressure on back and heat
-if it could be placed on top it would almost eliminate heat loss but would get in the way
-forced air is more effective and super cheap

195
Q

Quickest non-invasive way to cool a pt down

A

water immersion
-not practical tho

196
Q

Best drugs to give to induce tolerance to hypothermia are:

A

buspirone and meperidine
-work synergistically to drop shiver threshold to 34*C with little resp toxicity or sedation

197
Q

Benefits of therapeutic hypothermia surrounding ischemia

A

-improves brain/other tissue oxygenation by decreasing demand, slowing CBF, and allowing for aerobic metabolism in the face of ischemia or low O2, which decreasing release of lactic acid and superoxide radicals (free radicals)

-decreased release of excitatory amino acids and provides membrane stabilization

-cerebro-protective; cardio-protective (for ischemia)

198
Q

Hypothermic impact on heart

A

-decreased HR
-increased contractility
-maintained SV
-decreased CO and BP
-SA node and ventricular instability with decreasing temps (25-30*C Vfib more easily and defib won’t work)

199
Q

Hypothermic impact on kidneys and liver:

A

Kidneys:
-increased renovascular resistance -> decreased blood flow
-inhibits tubular absorption, normal urinary volume
-inhibits reabsorption of Na+ and K+ -> cold diuresis but maintains serum levels
-normal renal function when rewarmed

Liver:
-low hepatic blood flow and function cause significantly inhibited metabolism of some drugs

200
Q

Alpha stat does what?

A

ectothermic strategy to maintain temp, constant imidazole ionization causes optimal enzyme function as temp changes
-promotes removal of acidic products of intracellular metabolism
-works similarly to pH stat but pH stat works more efficiently

201
Q

How are fever and hyperthermia different?

A

fever is a thermoreg response to ENDOGENOUS pyrogens increasing the target core temp while increasing immune response

MAJOR KEY: fingers
-pts with fever and increasing core temp will have CONSTRICTED fingertips
-pts with other hyperthermia will have VASODILATED fingertips

202
Q

What are examples of endogenous pyrogens and what activates them?

A
  • interleukin-1, tumor necrosis factor, interferon-alpha, and macrophage inflammatory protein-1

-vagal afferents activate them

203
Q

Causes of fever:

A

-infection (most common)
-urologic manipulation
-mismatched blood
-blood entering 4th cerebral ventricle
-allergic reactions
-sometimes just happen postop

204
Q

Why is treating fever hard as CRNA?

A

-often hard to know source of fever or if source is known it could be unresponsive to tx

-some fevers are mediated by mechanisms that bypass effects of antipyretics

-active cooling takes a while and it can trigger thermoreg responses making situation worse (shivering, ANS activation) and pt uncomfortable

-make sure benefits outweigh risks with active cooling if taking that approach

205
Q

Most common electronic thermometers are:

A

thermistors or thermocouples
-good for clinical use
-infrared ones are NOT good for clinical use

206
Q

Core temp measurement during anesthesia is necessary to accurately detect hypothermia, overheating, and MH. Approved methods for this include:

A

-tympanic membrane via thermocouple
-PA cath
-DISTAL esophagus
-NASOpharyx

-these remain reliable even with cardiopulmonary bypass

207
Q

Muscle and skin temp measurement helps examine _ and ensure validity of _ monitoring

A

vasomotion
PNS monitoring

-does NOT confirm signs of MH bc will be considerably lower than core temp

208
Q

Which temp measurement method/s are used to determine thermoreg effects of anesthetics?

A

BOTH core and skin temps
-help estimate mean body temp and heat content (bc temps are not uniform thru body)

209
Q

Esophageal stethoscope temp probe is most reliable when it is positioned where?

A

-point of maximal heart sounds or even lower/ more distal

210
Q

Why are bladder and rectal temps not considered core temps?

A

rectal temps lag and are considered “intermediate”

bladder temps fluctuate with urine flow so not reliable

211
Q

T/F core temps are the best way to evaluate if pt is rewarmed properly

A

false
-BOTH core and INTERMEDIATE (rectal)

212
Q

T/F MH is best detected by an increasing core temp

A

false
-best DETECTED by tachycardia and increased EtCO2
-high core temp helps CONFIRM diagnosis

213
Q

T/F Amide LA and sedatives cause MH

A

false

214
Q

2 steps of hypothermia:

A
  1. redistribution of body heat from core-peripheral tissue
    2.heat loss exceeding metabolic heat production

NA 1 (31 decks)

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