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NUNA 690 - Principles > Hypothermia > Flashcards

Hypothermia Flashcards

1
Q

Homeothermic

A

Requires a nearly constant internal body temperature (humans are homeothermic)

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2
Q

Poikilothermic

A

Organism takes on the temperature of the surrounding environment (reptiles, humans under anesthesia)

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3
Q

Core temperature locations

A

Abdomen, thorax, head

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4
Q

What brain region uses negative and positive feedback to minimize perturbations from set preset “normal” temps?

A

Hypothalamus

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5
Q

Kilocalorie

A

Amount of heat needed to raise the temperature of 1 kg of water 1 degree Celsius; 1000 calories

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6
Q

Thermoregulation normally maintains core body temperature within ___ degrees Celsius of “normal” (~__ degrees Celsius)

A

0.2; 37

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7
Q

Thermolysis (4 mechanisms)

A

Conduction, evaporation, radiation, convection

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8
Q

Thermogenesis (4 mechanisms)

A

Nonshivering, shivering, diet induced, basal metabolic rate

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9
Q

What can change body temperature from normal? (9)

A

Circadian rhythm, exercise, food intake, infection, thyroid function, age, drugs (anesthesia, sedatives, alcohol), obesity, problems with hypothalamus

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10
Q

Thermoregulation is _______ in infants but frequently ________ in elderly

A

intact; impaired

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11
Q

In both genders, daily fluctuating temperature peaks around _____ (time of day) and is at its lowest in _____ __ hours

A

6 PM; early AM

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12
Q

Afferent temperature sensors gather temperature information from thermally sensitive cells:
- __ fibers are (myelinated/unmyelinated) and (small/large) and sense dull pain and warmth

A

C; unmyelinated; small

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13
Q

Afferent temperature sensors gather temperature information from thermally sensitive cells:
- ___ fibers are _____ myelinated and sense ____ pain and cold

A

A delta; thinly; sharp

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14
Q

Afferent temperature sensors are located in the _______ _________ of the dorsal horn of the spinal cord and carry signals to the ____________, the temperature regulating center.

A

substantia gelatinosa; hypothalamus

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15
Q

What is the first and most consistent response to hypothermia?

  • Can decrease heat loss by __ to __%
  • It is more energy efficient than _________
A

Vasoconstriction; 25; 50; shivering

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16
Q

Shivering is an inefficient means of heat production and can increase whole-body O2 consumption by _ to _x!

A

2;5

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17
Q

________ and ________ do not shiver but use non-shivering thermogenesis.

A

Newborns; infants

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18
Q

Non-shivering thermogenesis is accomplished by ANS fibers (____ receptors) innervating the _____ fat. This ______ the heat production in infants but increases it only slightly in adults.

A

beta; brown; doubles

Found in scapula, neck, back, and viscera especially in infants; stimulates lipolysis with heat release

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19
Q

Basal metabolic rate peaks at age _; for each _ degree Fahrenheit change, BMR changes by _%

A

2; 1; 7

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20
Q

_____ is the most important insulator against heat loss

A

Skin

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21
Q

Normothermia range in degrees Celsius

A

36-37

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22
Q

Mild hypothermia range in degrees Celsius

A

34-35.9

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23
Q

Moderate hypothermia range in degrees Celsius

A

32-33.9

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24
Q

Severe hypothermia range in degrees Celsius

A

<32

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25
Most metabolic heat is produced in the ____ compartment; _________ temperature is normally _ to _ degrees Celsius cooler; this is maintained by _____ __________. Anesthesia-induced __________ allows ____ heat to flow ___________.
core; peripheral; 2; 4; tonic vasoconstriction; vasodilation; core; peripherally
26
Radiation
Electromagnetic heat waves emanate from all surfaces; increased rate of radiation when temperatures are higher than the surrounding air
27
__________ is the major type of heat loss in the awake and surgical patient.
Radiation
28
Conduction
Transfer of heat between two adjacent surfaces; requires direct contact; molecule to molecule transfer of heat; warmer surface loses heat to cooler surface (ex., jelly padding in OR)
29
Convection
Loss of heat to air currents (wind chill); normally hair on our bodies trap air in surface layer of skin and counter convection forces
30
Evaporation
Loss of heat via water loss from the skin and mucus membranes
31
Percentages for mechanisms of heat loss - Radiation __% - Evaporation __% - Convection __% - Conduction _%
60; 22; 15; 3
32
With regards to convection, air speeds are typically 20 cm/s but ________ in ORs with _______ flow.
20; laminar
33
Bair hugger can prevent _______ and ________ heat loss
radiation; convection
34
OR foam pad is an excellent thermal insulator and prevents _________ heat loss
conduction
35
Evaporation from open _______ _______ or ______ ______ may be a significant source of heat loss in the OR
surgical wound; burn wounds
36
What percent of anesthetics cause hypothermia?
100%
37
How does anesthesia impact temperature regulation? (4 ways)
1. Skeletal muscle relaxation (no shivering) 2. Vasodilation 3. Decreased BMR (20-40%) 4. Impairs non-shivering thermogenesis
38
Describe the 3 phases of hypothermia under anesthesia.
- Phase I: a quick drop in temperature (first hour; 37 to 35 degrees C) - Phase II: slower phase (hours 1-4; 35 to 34 degrees C) - Phase III: the longest phase where temperature remains low
39
Describe the 3 phases of hypothermia under anesthesia.
- Phase I: a quick drop in temperature (first hour; 37 to 35 degrees C); redistribution of heat from core to periphery - Phase II: slower phase (hours 1-4; 35 to 34 degrees C); heat loss to environment exceeds heat production - Phase III: the longest phase where temperature remains low; metabolic heat production matches heat loss
40
How does heat loss compare in epidural/spinal anesthesia alone, general anesthesia, and the two methods used together?
General anesthesia causes greater overall and systemic heat loss; regional anesthesia causes more local hypothermia, having a less significant effect on the core temperature. The two anesthetics combined have the greatest effect of all, and the core temperature drop continues during phase III.
41
How does anesthesia impact warm and cold response thresholds?
Anesthesia increases the warm response threshold and decreases the cool response threshold so that the body will only cool at higher temperatures and warm at lower temperatures.
42
The interthreshold range of mean body temperature increases __ to __ fold under anesthesia.
10; 20
43
An operating room greater than __ degrees C is required for most adult patients to maintain normothermia.
24 (~75.2 degrees F)
44
Shivering (does/does not) occur in the neonate and is __________ developed in infants.
does not; incompletely
45
What body composition factors subject infants to higher heat loss from evaporation?
Thinner skin and subcutaneous fat
46
Infant body surface area relative to their weight is ___x that of an adult
2.5
47
What is the most important source of heat production for infants?
Non-shivering thermogenesis
48
True/False: Temperature monitoring is optional in pediatric patients due to efficient thermogenesis.
FALSE. Temperature should be monitored in ALL pediatric patients. Axilla site is usually sufficient, but esophageal or rectal can be used for major surgeries.
49
What mechanisms result in thermoregulatory failure in the elderly? (5)
Slowed blood circulation, thin skin, decreased BMR, decreased lean muscle mass (delayed/ineffective shivering), blunted vasoconstrictor response
50
Consequences of postop shivering (6)
Oxygen consumption increased up to 5x; increased intraocular pressure and ICP; increased blood loss and need for transfusion; tripled incidence of morbid cardiac outcomes; tripled incidence of surgical wound infections; enhanced drug effects and prolonged PACU stay
51
What meds can be given for postoperative shivering?
IV meperidine 25 mg or clonidine 75 micrograms and supplemental O2
52
By what mechanisms does hypothermia increase surgical blood loss?
Cold-induced defect in platelet function (without deficiency in number of platelets); impaired coagulation cascade enzymes; most drastic effects seen <34 degrees C
53
By what mechanisms does hypothermia increase morbid cardiac events?
Increased circulating norepinephrine (5x) and hypertension caused by vasoconstriction
54
What EKG changes can be seen with hypothermia, and what do they represent?
J wave/Osbourne wave; probably signifies intraventricular conduction defect; most often seen in <35 degrees C; bradycardia in infants
55
Which direction does hypothermia shift the oxyhemoglobin dissociation curve?
Left
56
By what mechanisms does hypothermia increase postoperative infection?
Vasoconstriction and impaired immune response
57
How does hypothermia impact potency and duration of anesthetics?
Duration of vecuronium >2x with -2 degrees C; MAC -5% for each -1 degree C; plasma concentrations of propofol +28% with hypothermia; metabolism enzymes are temperature-sensitive.
58
Complete anesthesia at brain temp of __ degrees C
20
59
What are methods of preventing heat loss? (5)
Blankets, forced air warming devices, heated humidification of inhaled gases, warming IV and irrigation fluids, raising ambient temperature
60
1 unit of refrigerated blood (_ degrees C) or 1 liter crystalloid administered at room temp (__ degrees C, __ degrees F) decreases mean body temperature ~___ degrees C; warm fluids to __ degrees C if >_ liters/hour
4; 26; 68; 0.25; 40
61
What is the most effective noninvasive means of heat conservation?
Forced air warming devices; rewarms at 2.5 degrees C/hr
62
Cutaneous heat loss from extremities makes up __%; thorax/abdomen __%; head __%; respiratory tract __%
60; 20; 10; 10
63
A single layer of blankets reduces heat loss by __%
30
64
________ induction causes more core hypothermia than _________ induction due to vasodilation.
Propofol; sevoflurane The massive vasodilation caused by propofol induction during the first 15 minutes of anesthesia is maintained and leads to overall greater hypothermia than an anesthetic with sevoflurane induction.
65
Benefits to hypothermia (3)
Substantial cerebral and spinal cord protection against ischemia; malignant hyperthermia decreased (in swine); multiple sclerosis patients benefit from hypothermia
66
True/false: Hypothermia is merely a patient comfort issue and does not increase hospital expenses.
FALSE!! Delayed anesthesia recovery+ prolonged hospital stay + adverse outcomes can cost >$3065/patient compared to $16 to use convection and IV fluid warmers.
67
Where can we monitor core temperature?
Nasopharyngeal, tympanic, PA catheter, eseophageal (lower 1/3 esophagus)
68
Where can we monitor intermediate temperature?
Rectal, bladder, axillary

NUNA 690 - Principles (5 decks)

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