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83 Cards in this Set

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the most common temperature disorder in the OR
hypothermia
temperature monitoring in the OR is considered a
standard of care - unless procedure is less than 15 minutes
definition of hypothermia
less than 36 degrees Celsius
core temperature is
the temperature of the blood perfusing the hypothalamus
hypothermia is associated with
several physiological changes and an increase in mortality
why is thermoregulation difficult for patients in the OR
because that ability is abolished by anesthesia - no shivering, no functioning hypothalamus under anesthesia
heat regulation is controlled by
the hypothalamus
heat production is adjusted by
changing metabolic rates (shivering, muscle movement)
heat loss is regulated through
vasodilation, blood shunting, sweating, respiratory tract evaporation
how is temperature and the rate of metabolism related?
the metabolic rate decreases 7% for each degree centigrade reduction
mechanisms of heat loss
radiation, convection, conduction, evaporation
function of the skin
to support, insulate, and protect against heat loss
hypothermic therapy is used in
neuro and cardiac arrest off bypass surgeries - decreases metabolic rate so significantly that O2 demand is almost nonexistant
snake-like
poikilothermic
what % of patients are hypothermic in the PACU
60 - 80%
patients at greatest risk of hypothermia
infants, elderly, hypothyroid, hypothalamic lesions
patients at some risk of hypothermia
burns, trauma, major hemorrhage, lengthy surgeries, abdominal and thoracic operations,
why are infants at greater risk of hypothermia
surface ratio and thin skin
why are the elderly at greater risk of hypothermia
poor regulation, thin fat, intolerant of cold
the core temperature under general anesthesia generally drops how much in the first hour
1 - 2 degrees C
explanation of rapid heat loss in OR
vasodilation caused by general anesthetics redistributes blood away from the core and too the periphery causing rapid cooling
describe the 3 phases of temperature dropping in the OR
phase I - drops about 2 degrees in first hour
phase II - drops to about 33.7 over next 3 hours
phase III - steady state at about 33.7 C
does regional anesthesia produce hypothermia
yes - but through a different mechanism - sympathetic blockade and vasodilation
radiation accounts for what % of heat loss
60%
radiation is
heat loss to the environment
radiant heat loss is dependent on
cutaneous blood flow and exposure of body surfaces to the environment
most effective way to combat radiant heat loss
increase the room temperature
the sun heat the earth through
radiation
means of preventing radiant heat loss
increase room temperature, heat air above or around patient, cover surface area with blankets or a plastic barrier between the environment and the patient (garbage bag for babies works well)
convection is
due to air current of movement of a gas
convection accounts fo what % of heat loss
15%
why is convection significant in the OR
air volume turnover is 10 - 15 times per hour
prevent convection by
covering a patient or creating a barrier
conduction accounts for what % of the heat loss
3%
conduction is
heat loss through direct contact with the skin to the surface os something else. it is the transfer of heat to adjacent molecules outside the body
conduction loss is determined by
amount of surface area in contact with the object and the temperature difference between the two objects and the thermal conductivity of an object
example of conductivity
standing in cold water, pouring irrigation fluid into a body cavity
what % of heat loss is accounted for by evaporation
20% (if not sweating)
sweating increases evaporation heat loss by
ten fold
evaporation is when
the sweat evaporates from your sking carrying the heat with it
evaporation occurs through
the skin, wet tissues, lung exhalation
evaporative heat loss depends on
exposed surface area and the relative humidity of the ambient gas
burns lose the most heat through what process
evaporation because they do not have skin
factors that contribute to heat loss in anesthesia
an ambient temperature < 24, low basal metabolic rate, large surfae are relative to body weight, vasodilation from drugs, no shivering, ventilating with cold, dry gases, iv infusion of cold fluids, cold irrigations, long OR time
body surface area to weight ratio of infant compared to adult
2 to 2.5 times greater
evaporation occurs through
the skin, wet tissues, lung exhalation
evaporative heat loss depends on
exposed surface area and the relative humidity of the ambient gas
burns lose the most heat through what process
evaporation because they do not have skin
factors that contribute to heat loss in anesthesia
an ambient temperature < 24, low basal metabolic rate, large surfae are relative to body weight, vasodilation from drugs, no shivering, ventilating with cold, dry gases, iv infusion of cold fluids, cold irrigations, long OR time
body surface area to weight ratio of infant compared to adult
2 to 2.5 times greater
why do infants get cold easily in or
body surface ratio, little subq fat, alveolar ventilation, lack of shiver, and immature sweat glands
what's with infant alveolar ventilation and cold?
ventilation rates 2 - 2.5 times more per kg than adults - therefore more heat loss through exhalation replaced with our cold, dry air
mechanism of heat production in newborns
they do not shiver - they metabolise brown fat and accounts for 6% of the newborns body weight
why do preemies have trouble regulating their heat
they have not had time to lay down the brown fat that they would have if they were a newborn
where is brown fat located
nape of the neck, the mediastinum, between the scapula and by the kidney and adrenal glands
brown fat cells have
lots of mitochondria, blood and sympathetic nerve supply
hypothermia activates the sympathetic or parasympathetic nervous system
sympathetic
hypothermia in an infant triggers
sympathetic stimulation, norepi release, increased O2 consumption, hydrolysis of brown fat to free fatty acids and glycerol
why do infants have trouble dissipating heat
no sweat glands
if you are heating the tubing for a newborn then
watch for condensation in the tube to prevent drowning
temperature monitoring sites
tympanic, nasopharynx, pulmonary artery, esophageal, bladder, axilla, sking
core temps are
tympanic, esophageal, nasopharynx, pulmonary artery
why do we like esophageal temps
ease of access, core temp, and incorporates an esophageal stethoscope
problem with rectal temps
slow to respond to changes in the core temperature
axillary accuracy is dependent on
proper placement and skin perfusion
physiological complications of hypothermia <37
arrhythmias (AV blocks), respiratory depression, enzymatic and coagulation factor dysfunction of the clotting system (prolonged refactory period in nodal tissue) - also will get oozy
physiological complications of hypothermia <33
bradycardia, myocardial depression, VF, shivering stops
at 30 degrees celsius the body experiences
coma and relative thrombocytopenia
cardiovascular events associated with hypothermia
vasoconstriction, increased SVR, ventricular arrythmias, bradycardia, and myocardial depression
metabolic events associated with hypothermia
decreased metabolic rate (decreased O2 demand so sometimes is good), decreased tissue perfusion, and acidosis or hyperglycemia
hematologic events associated with hypothermia
increased viscosity, left shift of oxyhemoglobin dissociation curve (harder to get O2 off to the tissue), impaired coagulation, thrombocytopenia
neurologic events associated with hypothermia
decreased cerebral blood flow, increased cerebral vascular resistance, drowsiness, confusion, lethargy, coma
drug clearance affected by hypothermia by
decreased hepatic and renal blood flow, decreased drug clearance, therefore need less drugs to keep patient asleep
anesthetic effects of hypothermia
decreased MAC, and delayed emergence (a reduction in blood flow decreases the minimal alveolar concentration of volatile anesthetic needed to keep a patient asleep)
why does hypothermia cause delayed emergence from anesthesia
reduction in blood flow through the tissues including the lungs and a reduction in CO2 production due to a reduction in the metabolic rate results in less of a stimulus to breathe
shivering increases heat production by
100 - 300%
shivering increases oxygen consumption by
500%
to fix shivering
warm the patient and give demerol
how to prevent shivering in the OR
raise the room temperature, cover exposed surfaces, forced air warming, warm IV fluids, warming blankets underneath patient, radiant warmers, warm irrigation fluids
HME stands for
humidified moisture exchanger
heated circuits should
not exceed 105F because it will scald the airway - usually just using a circle unit with an HME is sufficient (passice heat exhangers)
heat loss prevention in the anesthesia stuff
closed circuit, low flow rates, heat circuit are, HME
in sever cases of hypothermia do
warm gastric lavage
warm peritoneal lavage
warm bladder lavage
cardiopulmonary bypass