Thermoregulation - Exam 3 Flashcards
4 ways body loses heat:
-RADIATION (#1 in and out of OR)
-convection
-conduction
-evaporation
What is normal body temp roughly?
37*C
3 phases of thermoregulation:
afferent sensing
central regulation
efferent response
T/F thermoregulation works via negative feedback
false,
BOTH + and - feedback
Warm receptors increase firing rates as temperature _.
increases
-RECEPTORS fire, not EFFECTORS
Cold signals travel via _ fibers and warm signals travel via _ fibers
cold - A delta
warm - UNmyelinated C
-sometimes an overlap
Temperature sensors appear to be a class of _ _ _ protein receptors
transient receptor potential (TRP)
ASCending thermal info travels via the _ tract which is in the _ spinal cord
spinothalamic
anterior
-not in any specific spinal tract, involves many
T/F Complete destruction of the hypothalamus would ablate thermal RESPONSE
false; the ANTERIOR SC, not hypothal
- adaptive measures exist to regulate
ex) high SC transection can still provide thermoreg sometimes
T/F C fibers sometimes struggle to distinguish between intense cold and dull pain
False
-intense HEAT and SHARP pain
Temperature is regulated by central structures (hypothal) receiving integrated thermal inputs from _ , _, and _ and comparing them with _ temperatures for each thermoreg response
skin surface
neuraxis
deep tissue
THRESHOLD TEMPS
Some thermal input/output is “preprocessed” in the _ _
spinal cord
-preset responses not needed to be processed by hypothal
Gain =
intensity
-seen as a slope; end of slope = max intensity
Body’s normal determination of absolute temp threshold seems to be mediated by:
-NE
-dopamine
-5-hydroxytryptamine (nerd for “SEROTONIN” or “5-HT”)
-ACh
-Prostaglandin E
-neuropeptides
Pt related factors that affect temp threshold:
-circadian rhythm
-monthly cycle (0.5*C change in women)
-food intake
-infection
-hypo/hyperthyroidism
-natural adaptations
-drugs/alcohol/nicotine/etc
Skin temp contributes _ % to control of each thermoreg defense
20%
Control of AUTONOMIC responses is ~ _ % determined by thermal input from core structures
80%
Most of input controlling BEHAVIORAL responses is derived from the _ _
skin surface
The interthreshold range is the range of temperatures in which core temps aren’t triggering an _ response
autonomic
-varies by few tenths of degree centigrade
T/ F The upper limit of the interthreshold range is the sweating threshold and the shiver threshold on the low end
FALSE!
sweating and vasoconstriction
The relationship between skin temp and core temp triggering vasoconstriction and sweating is _
linear
During the menstrual cycle, the follicular phase (pre-ovulation) has _ temperature than the luteal phase (post-ovulation)
lower
Even during the follicular phase, a woman’s sweating and vasoconstriction thresholds are -*C higher than in men
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
Who sucks at central thermoreg control more, old ppl or premature infants?
old ppl
The body likes the path of least metabolic resistance, which happens first, shivering or vasconstriction?
vasoconstriction
-more energy efficient
The interthreshold range in humans is usually only _ *C
0.2*C
3 things can happen when core temp is below interthreshold range:
-vasoconstriction
-nonshivering thermogenesis
-shivering
2 things can happen when core temp is above interthreshold range:
-vasodilation
-sweating
_ determine the ambient temp range that the body will tolerate while keeping a normal core temp
Effectors
T/F If an effector is inhibited(like shivering after a NMBD), the tolerable range will decrease and so will total body temp
false,
compensatory mechs in place to correct this until they they too fail
QUANTITATIVELY, which type of effector temp regulation mechanism is most important?
Behavioral
-putting on more clothes, staying away from cold/heat/etc
T/F Decreased muscle mass, NM disease, and taking muscle relaxants increase shivering and lower the minimum tolerable ambient temp.
False
MR drugs and these things INHIBIT shivering and INCREASE minimum tolerable ambient temp
Anticholinergics inhibit the _ ganglionic cholinergic nerves responsible for sweating and _ the maximum tolerable temp
postganglionic
decrease
-ex) atropine admin will inhibit sweating
Which effector is the most consistently used autonomic mechanism?
cutaneous vasoconstriction
Vasoconstriction reduces which 2 forms of metabolic heat loss from skin?
convection
radiation
Total digital skin blood flow is divided into _ (capillary) and _ (AV shunt)
nutritional
thermoregulatory
T/F AV shunts are anatomically and functionally similar as capillaries and vasoconstrictions can cause peripheral issues
False
-theyre structurally/functionally different and so nutrient-dense blood is not constricted away from periphery
Shunts are about _ mcm in diameter and capillaries are about _mcm
100mcm
10mcm
-therefore shunts can carry 10k x more blood than capillaries of equal length
AV shunts are all or nothing and have _ gains over _ changes in core temp
high
small
Thermoregulatory AV shunts ability to constrict is mediated by local _ adrenergic _ nerves and minimally by circulating _
alpha adrenergic sympathetic n
catecholamines
About _% of cardiac output traverses AV shunts and vasoconstriction of these can cause a increase MAP by about _mmHg
10%
15mmHg
ALL GA markedly impair normal ___________ thermoreg control
Autonomic
Anesthetics cause warm thresholds to _________ slightly and cold response thresholds to drastically ________.
increase
reduce
Anesthetics cause the interthreshold range to increase from 0.3C to about ___ to ___ deg C
2 to 4 deg C
-from increased sweating and reduced vasoconstriction thresholds
-pt is poikilothermic in this range
T/F: Anesthesia decreases all thermoreg responses, gain, and maximum intensity.
False, some responses remain normal
**BIG MONEY*
For Anesthetics like Desflurane, alfentanyl, Dexmedetomidine, and propofol, the sweating threshold will slightly _______ while markedly + synchronously _______ the vasoconstriction and shivering thresholds.
increase
decrease
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
0.2deg C to 2-4deg
poikilothermic
N20 decreases vasoconstriction and shivering thresholds ____than equipotent concentrations of volatile anesthetics.
less
T/F: Midazolam severly impairs thermoreg control.
false, minimally
Painful stim slightly ______ vasoconstriction thresholds, so thresholds are _________ with the use of local or regional anesthetics
increases
decreased
T/F: 3 Cold responses in anesthetized adults include: vasoconstriction, nonshivering thermogenesis, and shiver.
False, non-shiver thermogen doesn’t occur w/ adults under GA
T/F: Nonshiver thermogen increases metabolic rate in infants after propofol admin.
False, no bueno, babies rely on this a lot
Shiver threshold is about ___ deg C less than the vasoconstriction threshold and _____ occurs in surgical doses of GA.
1degC
rarely
The best preserved thermoreg defense during GA is _____
sweating
Under GA, sweat threshold is slightly _____ and gain and max intensity are _____
increased
normal
The efficacy of which 2 thermoreg defenses are diminished with GA?
vasoconstriction & shiver
Heat transfer via radiation is proportional to….
difference of the 4th power of the absolute temp difference between surfaces.
Think the Sun or Lights and your skin.
Conductive heat loss is proportional to….
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
Convective heat loss increases substantially in ORs that provide ______ Flow
Laminar
Evaporative heat loss from skin surfaces is < ___% of metabolic heat production in adults in the absence of sweating from GA
<10%
Population most at-risk from evaporative heat loss =
-premies (lose 1/5 of metabolic heat production via transcutaneous evap)
-large surgical wounds
-infants
-Hypothalamus
-other parts of brain
-spinal cord
-deep abdominal and thoracic tissue
-skin
EACH contribute to _% of total thermal input
20%
Sustained shiver increases metabolic heat production by -% unlike exercise which is 500%
50-100%
-shivering isn’t very efficient
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
250Hz
4-8 cycles/min
Sweating is efficient and dissipates about _ kcal/g of evaporated sweat
0.58kcal/g
Untrained people can sweat up to _L/hour
1L/hr – fluid loss!
-athletes can sweat 2L/hr
During extreme heat stress, the 1st mm of skin can have blood flow equaling _L/min which is normal whole resting cardiac ouput
7.5L/min
-vasodilation
Anesthetics change interthreshold range from 0.3C (I saw 0.2C somewhere else) to -*C
2-4*C
-20 fold increase in range
Most anesthetics except meperidine and nefopam cause vasoconstriction and shiver thresholds to _ while maintaining their _*C difference
decrease
1*C
VA with N2O or fentanyl _ the vasoconstriction threshold by 2-4C from _C
decrease
37*C
The vasoconstriction threshold is about _*C less in 60-80 year olds than in 30-50 year olds.
1*C
-elderly pts get more cold before their body tries compensating
The shiver threshold is usually _ *C less than the _ threshold
1*C
vasoconstrictionq
Radiation is proportional to (equals)
difference of the 4th power of the absolute temperature differences between surfaces
Convection is proportional to (equals)
square root of air speed
Air speed in OR is usually
20cm/sec
When not sweating, evaporative heat loss from the skin surface is < _ % of metabolic heat production
<10%
-when not sweating, heat loss from evap is not significant; radiation and convection are significant
Anesthetics decrease the metabolic rate by -%
20-30%
1st hr of anesthesia can drop core temp by -*C
0.5-1.5*C
Normally core temp represents only _% of body mass (head and trunk) and the remaining mass is about -*C cooler than the core temp
50%
2-4*C cooler elsewhere in body
After initial redistribution hypothermia, core temp decreases slowly and linearly for _-_hours
2-4 hrs
After _-_hrs of anesthesia, core temp reaches a plateau and stays pretty constant
3-4hr
Core temp plateauing after 3-4hr of anesthesia is due to _ vasoconstriction which is triggered by core temperatures of -*C
peripheral
33-35*C
-could also just be from heat production = heat loss and pt reaching steady state
Core temp dropping after anesthesia is 81% due to _
redistribution
Epidural and spinal blocks both cause _ vasoconstriction and shiver thresholds by _*C _ the level of the block.
decreased
0.6*C
ABOVE
Even short acting LA like 2-chloroprocaine with a half life of _ sec can impair thermoregulation
20 sec
Leg skin temps of _*C are needed to prevent cold response in an unanesthetized pt similarly to regional blocks
38*C
After epidural anesthesia, the gain for thermoreg defenses are decreased _ fold
3.7
Core temp usually decreases 0.5-1*C after _
induction
Regional and GA vasoconstriction thresholds are _*C less than GA thresholds alone
1*C
-adding regional to GA makes cold response thresholds even lower
The lower body contributes to _% of thermoreg control
10%
Antishiver drugs and doses DURING anesthesia:
-Meperidine 25mg IV or epidural
-Clonidine 75mcg IV
-Precedex
-Katenserin 10mg IV
-Mag sulfate 30mg/kg IV
Hypothermia of -C can be protective for cerebral ischemia and core temps of _C are sometimes used in neuro cases
1-3C
34C
Coag labs are processed at _*C so it is difficult to assess coag changes from hypothermia
37*C
Just a _*C drop in core temp can increase both blood loss and the risk of needing transfusions by _%
1*C
20%
The DOA of Vec is doubled when core temps are _*C less than normal
2C
-atracurium is less dependent but a 3C drop increases DOA by 60%
-this is due to pharmacoKINETIC effect, not pharmacodynamic
Even without MR, twitch responses are decreased by _ -_% when pt is hypothermic
10-15%
Neostigmine efficacy is _ during hypothermia but onset is _% longer than normal
unchanged
20%
3*C hypothermia causes a _% increase of plasma concentration of propofol
30%
The MAC of volatile anesthetics is _% less per _ *C drop from normothermia and this is due to hypothermia influencing the pharmaco- _ effects
5%,
1*C
pharmacodynamic
Core temps < _*C do not require anesthesia to prevent movement response from incision
20*C
Hypothermia increases infection risk and duration of hospitalization by _%
20%
_% of pts experience post anesthetic tremor/shiver
40%
Postop shivering increases O2 consumption by _%
100%
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
tonic
phasic
Cutaneous warming is not very effective is pt core temp is < _*C
< 35*C
POSTOP(not intraop) shiver treatment and doses:
-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
T/F Narcan reverses antishiver effects of meperidine
false
-only in large doses >5mg/kg/min
Normally, _% of metabolic heat loss is thru skin surface, with anesthesia, more is lost from _ and from cold _
90%
incisions
cold IV fluid
Prewarming for as little as _ min can prevent redistribution hypothermia
30min
T/F Respiratory tract has a significant role in heat loss
false, <10%
Who benefits from cutaneous skin warming more, kids or adults?
kids
10x more effective
1 unit of refrigerated blood or 1L of ROOM TEMP crystalloid can drop mean body temp by _*C
0.25*C
-this is bc 1 unit of COLD blood is about half of volume of 1L of ROOM TEMP crystalloid
COLD IV fluid can drop mean body temp by _ C and ROOM TEMP IV fluid can drop it by _C
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
Room temp required to maintain normothermia is >_C in adults and >_C in infants
> 23C
26C
Single layer of insulation reduces heat loss by _%.
30%
-adding 3 layers = 50%
-diminishing return!
90% of metabolic heat loss is thru skin so only _ _ can transfer enough heat to prevent hypothermia
cutaneous warming
T/F Burns happen when water temp is >40*C
false
they can happen before that
When cutaneous heat loss is eliminated, metabolic heat production increases mean body temp by _*C / hr
1*C
Target temp for mild therapeutic hypothermia is a core temp between:
32-34*C
T/F Forced air COOLING is efficient
false
-takes 2.5 hr to cool pts to 35*C
_ cooling is the most effective way to decrease temperature and does so at a rate of _*C/hour
Endovascular
4*C/hr
-invasive, requires a heat exchange catheter in the IVC via a fem line
_ and meperidine synergistically reduce the shiver threshold to _ *C with minimal sedation and respiratory toxicity
Buspirone
34*C
Deep hypothermia (28C) was used for CABGs in past but they now perform them at _C or normothermia
33*C
Deep hypothermia of _*C is used for intentional circulatory arrest
18*C
Whole body metabolic rate decreases with hypothermia at a rate of _%/C and reaches a 50% metabolic rate at _C
8%/C drop
50% rate by 28C
Cerebral function is maintained until core temp reaches _C and loss of consciousness occurs at _C
33C
28C
-SSEPs decrease at 33*C
Primitive reflexes(gag, pupil, spinal reflexes) remain intact until core temp reaches_*C
25*C
Nerve conduction _ but peripheral muscle tone _ causing tension and myoclonus at core temps of _*C
decreases
increases
26*C
SA pacing and ventricular irritability occur when core temps <_C. Fibrillations occur between -C and defib will _ work
<28C
25-30C
defib will NOT work!
Temps < _ *C will decrease respiratory strength but CO2 ventilatory drive will not change
<33*c
For each 1*C drop in core temp, pH of blood _ by 0.0017 units
increases
-colder pts will be more ALKALOTIC!!
Hypothermia causes a _ shift in the oxyhemoglobin association curve but _ metabolic rate
LEFT shift
decreases
What is pH stat?
Body’s attempt to regulate blood pH at 7.4
During MH, circulating catecholamine concentration is 20x the average, and the resulting vasoconstriction compromises _ heat loss mechanisms
efferent
When pregnant pt is hyperthermic with an epidural and laboring for > _hrs, what happens next?
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
WHY do we not need to monitor temp if case is <30 mins?
bc core temp changes are difficult to interpret at this point
When must temperature monitoring occur?
-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
80% of thermal input is derived from _ _
core temp
GA decreases the hypothermia response thresholds from _C to -C
37C
33-35C
Keep the pts core temp _*C unless otherwise indicated for the case
36*C
Clonidine synchronously _ cold response thresholds and slightly _ sweat thresholds
decrease
increase
Which VA causes AV shunt vasoconstriction gain to decrease threefold while preserving its max intensity?
Desflurane
T/F Vasoconstriction usually prevents additional hypothermia so even unwarmed pts rarely are cold enough to shiver
true
-during anesthesia tho pts are not able to increase heat PRODUCTION to outweigh hypothermia
Gain and max intensity of shiver stays the same with admin of which 2 drugs:
meperidine and alfentanil
Gain is _ with N2O use and max intensity is _
unchanged
decreased
2 reasons for hypothermia:
anesthetic impaired thermoreg and exposure to cold OR environment
VA cause vasodilation via _ peripheral action and _ tonic thermoreg vasoconstriction, causing AV shunt dilation
direct
inhibit
T/F Body heat is evenly distributed
false
Core to peripheral tissue temp gradient is normally preserved by _ _ _.
tonic thermoreg vasoconstriction
-blunted by GA
Anesthetic induced vasodilation warms arms and legs at the expense of the _
core
-extent of redistribution of heat depends on core-peripheral temp gradient before induction
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
true
Threshold decreases seen in regional anesthesia are NOT from redistribution but from altered _ control from altered AFFerent input from _
central
legs
-redistribution still happen tho
The skin temp on the legs is dependent on _ cold signals
tonic
Regional anesthesia blocks _ thermal input from blocked regions and this is usually _ information, causing brain to assume legs are _.
all
cold
warm
-awake pts will know they are not warm, but will “feel” warm
T/F IV LA causes decreased thresholds
false
Normally, leg temps of _*C can blunt cold responses but _ anesthesia can mimic this
38*C
regional
Regional anesthesia _ gain and max intensity of shiver and vasoconstriction by half of what is normal
reduces
-drugs usually given with regional, old age, and comorbidities add to this
T/F core hypothermia during regional anesthesia may not trigger a perception of cold
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!
T/F Regional anesthesia produces core-peripheral redistribution and reaches plateau just the same as GA.
False!
-there is no plateau with regional bc the block prevents vasoconstriction in the legs and core temp is further reduced from vasodilation
Will a pt receiving GA and regional reach a plateau core temp?
no
-v important to measure core temp!
T/F Temp of injected LA can influence incidence of shivering
false
Sometimes lwo intensity tremors happen with regional that aren’t associated with temperature but rather with _
pain
Protective action of hypothermia is associated with decreased release of excitatory _ _
amino acids
T/F Therapeutic hypothermia is best used in pts after ROSC from in-hospital cardiac arrest, neurosurgery, and for asphyxiated neonates
False!
-All are true but using post-arrest requires that pt experienced arrest OUT of hospital
T/F Allowing pts at risk for MH to be slightly hypothermic increases their risk of developing MH
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
Cold causing a defect in platelet function is related to _ temperature
local
-not core
Wound temperature is determined by _ temperature
core
-distinctly higher in normothermia
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
directly
Hypothermia influences immune function by:
-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
Postop thermal discomfort is distressing and can _ BP, HR, and plasma catecholamine concentration
increase
Most important consequence of mild hypothermia:
3x increase in morbid myocardial outcomes
T/F Myocardial ischemia is associated with shivering and increased O2 demand
false
Postop tremor/shivering can be from several causes:
-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
Postop shiver is different than normal shiver bc:
-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)
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
volatile anesthetics
descending
Non-thermoreg tremor similar to clonus is seen in laboring pts and is likely from _
pain
Will cutaneous warming for postop shiver work?
only a little if core temp is at or above 35*C
Clonidine and precedex are thought to work on the _ thermoreg system due to the fact that they both reduce vasoconstriction and shivering thresholds
central
Which is better at preventing/treating postop shiver, alfentanil or meperidine?
meperidine
-likely related to agonist activity at central alpha adrenoreceptor
Intraop hypothermia can be reduced by minimizing risks for cutaneous heat loss which happens via:
-cold OR environment
-evaporation from incision
-cold IV fluids
Mean body temp decreases when heat loss to environment is > :
metabolic heat production
_ 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
Vasomotor tone
Arteriolar tone
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?
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
Core warming is slower after GA postop bc vasoconstriction constrains up to _kcal in peripheral tissue
30kcal
Applied warming is most effective when pt is vasoconstricted or vasodilated?
vasodilated
-better to warm INTRAOP not POSTOP (easier to achieve and prevents complications)
-even better to warm in preop
Most important component of peripheral heat compartment:
legs
T/F Prewarming increases core temp significantly
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)
Heat loss via resp tract is minimal but occurs via heating and humidifying via the _ phase of breathing
inspiratory
-heat loss is NOT thru expiratory phase
-humidification costs the most heat of the two factors
Who benefits more from airway heating/humidification waming methods, kids or adults?
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”
Why is it impossible to heat ppl with heated IV fluid?
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!
Most critical factor influencing heat loss:
OR room temp
-determines rate of metabolic heat loss
EASIEST way to decrease cutaneous heat loss:
passive insulation
-1 layer = 30% less heat loss, diminishing return with more layers tho (3 layers only 50% decrease)
Which is more important, amount of skin covered or location of skin being covered?
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
Why are water circulating pads not great for warming?
-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
Quickest non-invasive way to cool a pt down
water immersion
-not practical tho
Best drugs to give to induce tolerance to hypothermia are:
buspirone and meperidine
-work synergistically to drop shiver threshold to 34*C with little resp toxicity or sedation
Benefits of therapeutic hypothermia surrounding ischemia
-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)
Hypothermic impact on heart
-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)
Hypothermic impact on kidneys and liver:
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
Alpha stat does what?
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
How are fever and hyperthermia different?
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
What are examples of endogenous pyrogens and what activates them?
- interleukin-1, tumor necrosis factor, interferon-alpha, and macrophage inflammatory protein-1
-vagal afferents activate them
Causes of fever:
-infection (most common)
-urologic manipulation
-mismatched blood
-blood entering 4th cerebral ventricle
-allergic reactions
-sometimes just happen postop
Why is treating fever hard as CRNA?
-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
Most common electronic thermometers are:
thermistors or thermocouples
-good for clinical use
-infrared ones are NOT good for clinical use
Core temp measurement during anesthesia is necessary to accurately detect hypothermia, overheating, and MH. Approved methods for this include:
-tympanic membrane via thermocouple
-PA cath
-DISTAL esophagus
-NASOpharyx
-these remain reliable even with cardiopulmonary bypass
Muscle and skin temp measurement helps examine _ and ensure validity of _ monitoring
vasomotion
PNS monitoring
-does NOT confirm signs of MH bc will be considerably lower than core temp
Which temp measurement method/s are used to determine thermoreg effects of anesthetics?
BOTH core and skin temps
-help estimate mean body temp and heat content (bc temps are not uniform thru body)
Esophageal stethoscope temp probe is most reliable when it is positioned where?
-point of maximal heart sounds or even lower/ more distal
Why are bladder and rectal temps not considered core temps?
rectal temps lag and are considered “intermediate”
bladder temps fluctuate with urine flow so not reliable
T/F core temps are the best way to evaluate if pt is rewarmed properly
false
-BOTH core and INTERMEDIATE (rectal)
T/F MH is best detected by an increasing core temp
false
-best DETECTED by tachycardia and increased EtCO2
-high core temp helps CONFIRM diagnosis
T/F Amide LA and sedatives cause MH
false
2 steps of hypothermia:
- redistribution of body heat from core-peripheral tissue
2.heat loss exceeding metabolic heat production
