Principles I - Hypothermia

Front 1

the most common temperature disorder in the OR

Back 1

hypothermia

Front 2

temperature monitoring in the OR is considered a

Back 2

standard of care - unless procedure is less than 15 minutes

Front 3

definition of hypothermia

Back 3

less than 36 degrees Celsius

Front 4

core temperature is

Back 4

the temperature of the blood perfusing the hypothalamus

Front 5

hypothermia is associated with

Back 5

several physiological changes and an increase in mortality

Front 6

why is thermoregulation difficult for patients in the OR

Back 6

because that ability is abolished by anesthesia - no shivering, no functioning hypothalamus under anesthesia

Front 7

heat regulation is controlled by

Back 7

the hypothalamus

Front 8

heat production is adjusted by

Back 8

changing metabolic rates (shivering, muscle movement)

Front 9

heat loss is regulated through

Back 9

vasodilation, blood shunting, sweating, respiratory tract evaporation

Front 10

how is temperature and the rate of metabolism related?

Back 10

the metabolic rate decreases 7% for each degree centigrade reduction

Front 11

mechanisms of heat loss

Back 11

radiation, convection, conduction, evaporation

Front 12

function of the skin

Back 12

to support, insulate, and protect against heat loss

Front 13

hypothermic therapy is used in

Back 13

neuro and cardiac arrest off bypass surgeries - decreases metabolic rate so significantly that O2 demand is almost nonexistant

Front 14

snake-like

Back 14

poikilothermic

Front 15

what % of patients are hypothermic in the PACU

Back 15

60 - 80%

Front 16

patients at greatest risk of hypothermia

Back 16

infants, elderly, hypothyroid, hypothalamic lesions

Front 17

patients at some risk of hypothermia

Back 17

burns, trauma, major hemorrhage, lengthy surgeries, abdominal and thoracic operations,

Front 18

why are infants at greater risk of hypothermia

Back 18

surface ratio and thin skin

Front 19

why are the elderly at greater risk of hypothermia

Back 19

poor regulation, thin fat, intolerant of cold

Front 20

the core temperature under general anesthesia generally drops how much in the first hour

Back 20

1 - 2 degrees C

Front 21

explanation of rapid heat loss in OR

Back 21

vasodilation caused by general anesthetics redistributes blood away from the core and too the periphery causing rapid cooling

Front 22

describe the 3 phases of temperature dropping in the OR

Back 22

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

Front 23

does regional anesthesia produce hypothermia

Back 23

yes - but through a different mechanism - sympathetic blockade and vasodilation

Front 24

radiation accounts for what % of heat loss

Back 24

60%

Front 25

radiation is

Back 25

heat loss to the environment

Front 26

radiant heat loss is dependent on

Back 26

cutaneous blood flow and exposure of body surfaces to the environment

Front 27

most effective way to combat radiant heat loss

Back 27

increase the room temperature

Front 28

the sun heat the earth through

Back 28

radiation

Front 29

means of preventing radiant heat loss

Back 29

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)

Front 30

convection is

Back 30

due to air current of movement of a gas

Front 31

convection accounts fo what % of heat loss

Back 31

15%

Front 32

why is convection significant in the OR

Back 32

air volume turnover is 10 - 15 times per hour

Front 33

prevent convection by

Back 33

covering a patient or creating a barrier

Front 34

conduction accounts for what % of the heat loss

Back 34

3%

Front 35

conduction is

Back 35

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

Front 36

conduction loss is determined by

Back 36

amount of surface area in contact with the object and the temperature difference between the two objects and the thermal conductivity of an object

Front 37

example of conductivity

Back 37

standing in cold water, pouring irrigation fluid into a body cavity

Front 38

what % of heat loss is accounted for by evaporation

Back 38

20% (if not sweating)

Front 39

sweating increases evaporation heat loss by

Back 39

ten fold

Front 40

evaporation is when

Back 40

the sweat evaporates from your sking carrying the heat with it

Front 41

evaporation occurs through

Back 41

the skin, wet tissues, lung exhalation

Front 42

evaporative heat loss depends on

Back 42

exposed surface area and the relative humidity of the ambient gas

Front 43

burns lose the most heat through what process

Back 43

evaporation because they do not have skin

Front 44

factors that contribute to heat loss in anesthesia

Back 44

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

Front 45

body surface area to weight ratio of infant compared to adult

Back 45

2 to 2.5 times greater

Front 46

evaporation occurs through

Back 46

the skin, wet tissues, lung exhalation

Front 47

evaporative heat loss depends on

Back 47

exposed surface area and the relative humidity of the ambient gas

Front 48

burns lose the most heat through what process

Back 48

evaporation because they do not have skin

Front 49

factors that contribute to heat loss in anesthesia

Back 49

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

Front 50

body surface area to weight ratio of infant compared to adult

Back 50

2 to 2.5 times greater

Front 51

why do infants get cold easily in or

Back 51

body surface ratio, little subq fat, alveolar ventilation, lack of shiver, and immature sweat glands

Front 52

what's with infant alveolar ventilation and cold?

Back 52

ventilation rates 2 - 2.5 times more per kg than adults - therefore more heat loss through exhalation replaced with our cold, dry air

Front 53

mechanism of heat production in newborns

Back 53

they do not shiver - they metabolise brown fat and accounts for 6% of the newborns body weight

Front 54

why do preemies have trouble regulating their heat

Back 54

they have not had time to lay down the brown fat that they would have if they were a newborn

Front 55

where is brown fat located

Back 55

nape of the neck, the mediastinum, between the scapula and by the kidney and adrenal glands

Front 56

brown fat cells have

Back 56

lots of mitochondria, blood and sympathetic nerve supply

Front 57

hypothermia activates the sympathetic or parasympathetic nervous system

Back 57

sympathetic

Front 58

hypothermia in an infant triggers

Back 58

sympathetic stimulation, norepi release, increased O2 consumption, hydrolysis of brown fat to free fatty acids and glycerol

Front 59

why do infants have trouble dissipating heat

Back 59

no sweat glands

Front 60

if you are heating the tubing for a newborn then

Back 60

watch for condensation in the tube to prevent drowning

Front 61

temperature monitoring sites

Back 61

tympanic, nasopharynx, pulmonary artery, esophageal, bladder, axilla, sking

Front 62

core temps are

Back 62

tympanic, esophageal, nasopharynx, pulmonary artery

Front 63

why do we like esophageal temps

Back 63

ease of access, core temp, and incorporates an esophageal stethoscope

Front 64

problem with rectal temps

Back 64

slow to respond to changes in the core temperature

Front 65

axillary accuracy is dependent on

Back 65

proper placement and skin perfusion

Front 66

physiological complications of hypothermia <37

Back 66

arrhythmias (AV blocks), respiratory depression, enzymatic and coagulation factor dysfunction of the clotting system (prolonged refactory period in nodal tissue) - also will get oozy

Front 67

physiological complications of hypothermia <33

Back 67

bradycardia, myocardial depression, VF, shivering stops

Front 68

at 30 degrees celsius the body experiences

Back 68

coma and relative thrombocytopenia

Front 69

cardiovascular events associated with hypothermia

Back 69

vasoconstriction, increased SVR, ventricular arrythmias, bradycardia, and myocardial depression

Front 70

metabolic events associated with hypothermia

Back 70

decreased metabolic rate (decreased O2 demand so sometimes is good), decreased tissue perfusion, and acidosis or hyperglycemia

Front 71

hematologic events associated with hypothermia

Back 71

increased viscosity, left shift of oxyhemoglobin dissociation curve (harder to get O2 off to the tissue), impaired coagulation, thrombocytopenia

Front 72

neurologic events associated with hypothermia

Back 72

decreased cerebral blood flow, increased cerebral vascular resistance, drowsiness, confusion, lethargy, coma

Front 73

drug clearance affected by hypothermia by

Back 73

decreased hepatic and renal blood flow, decreased drug clearance, therefore need less drugs to keep patient asleep

Front 74

anesthetic effects of hypothermia

Back 74

decreased MAC, and delayed emergence (a reduction in blood flow decreases the minimal alveolar concentration of volatile anesthetic needed to keep a patient asleep)

Front 75

why does hypothermia cause delayed emergence from anesthesia

Back 75

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

Front 76

shivering increases heat production by

Back 76

100 - 300%

Front 77

shivering increases oxygen consumption by

Back 77

500%

Front 78

to fix shivering

Back 78

warm the patient and give demerol

Front 79

how to prevent shivering in the OR

Back 79

raise the room temperature, cover exposed surfaces, forced air warming, warm IV fluids, warming blankets underneath patient, radiant warmers, warm irrigation fluids

Front 80

HME stands for

Back 80

humidified moisture exchanger

Front 81

heated circuits should

Back 81

not exceed 105F because it will scald the airway - usually just using a circle unit with an HME is sufficient (passice heat exhangers)

Front 82

heat loss prevention in the anesthesia stuff

Back 82

closed circuit, low flow rates, heat circuit are, HME

Front 83

in sever cases of hypothermia do

Back 83

warm gastric lavage
warm peritoneal lavage
warm bladder lavage
cardiopulmonary bypass