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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
Q

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 ___________.

A

core; peripheral; 2; 4; tonic vasoconstriction; vasodilation; core; peripherally

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26
Q

Radiation

A

Electromagnetic heat waves emanate from all surfaces; increased rate of radiation when temperatures are higher than the surrounding air

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27
Q

__________ is the major type of heat loss in the awake and surgical patient.

A

Radiation

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28
Q

Conduction

A

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
Q

Convection

A

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
Q

Evaporation

A

Loss of heat via water loss from the skin and mucus membranes

31
Q

Percentages for mechanisms of heat loss

  • Radiation __%
  • Evaporation __%
  • Convection __%
  • Conduction _%
A

60; 22; 15; 3

32
Q

With regards to convection, air speeds are typically 20 cm/s but ________ in ORs with _______ flow.

A

20; laminar

33
Q

Bair hugger can prevent _______ and ________ heat loss

A

radiation; convection

34
Q

OR foam pad is an excellent thermal insulator and prevents _________ heat loss

A

conduction

35
Q

Evaporation from open _______ _______ or ______ ______ may be a significant source of heat loss in the OR

A

surgical wound; burn wounds

36
Q

What percent of anesthetics cause hypothermia?

A

100%

37
Q

How does anesthesia impact temperature regulation? (4 ways)

A
  1. Skeletal muscle relaxation (no shivering)
  2. Vasodilation
  3. Decreased BMR (20-40%)
  4. Impairs non-shivering thermogenesis
38
Q

Describe the 3 phases of hypothermia under anesthesia.

A
  • 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
Q

Describe the 3 phases of hypothermia under anesthesia.

A
  • 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
Q

How does heat loss compare in epidural/spinal anesthesia alone, general anesthesia, and the two methods used together?

A

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
Q

How does anesthesia impact warm and cold response thresholds?

A

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
Q

The interthreshold range of mean body temperature increases __ to __ fold under anesthesia.

A

10; 20

43
Q

An operating room greater than __ degrees C is required for most adult patients to maintain normothermia.

A

24 (~75.2 degrees F)

44
Q

Shivering (does/does not) occur in the neonate and is __________ developed in infants.

A

does not; incompletely

45
Q

What body composition factors subject infants to higher heat loss from evaporation?

A

Thinner skin and subcutaneous fat

46
Q

Infant body surface area relative to their weight is ___x that of an adult

A

2.5

47
Q

What is the most important source of heat production for infants?

A

Non-shivering thermogenesis

48
Q

True/False: Temperature monitoring is optional in pediatric patients due to efficient thermogenesis.

A

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
Q

What mechanisms result in thermoregulatory failure in the elderly? (5)

A

Slowed blood circulation, thin skin, decreased BMR, decreased lean muscle mass (delayed/ineffective shivering), blunted vasoconstrictor response

50
Q

Consequences of postop shivering (6)

A

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
Q

What meds can be given for postoperative shivering?

A

IV meperidine 25 mg or clonidine 75 micrograms and supplemental O2

52
Q

By what mechanisms does hypothermia increase surgical blood loss?

A

Cold-induced defect in platelet function (without deficiency in number of platelets); impaired coagulation cascade enzymes; most drastic effects seen <34 degrees C

53
Q

By what mechanisms does hypothermia increase morbid cardiac events?

A

Increased circulating norepinephrine (5x) and hypertension caused by vasoconstriction

54
Q

What EKG changes can be seen with hypothermia, and what do they represent?

A

J wave/Osbourne wave; probably signifies intraventricular conduction defect; most often seen in <35 degrees C; bradycardia in infants

55
Q

Which direction does hypothermia shift the oxyhemoglobin dissociation curve?

A

Left

56
Q

By what mechanisms does hypothermia increase postoperative infection?

A

Vasoconstriction and impaired immune response

57
Q

How does hypothermia impact potency and duration of anesthetics?

A

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
Q

Complete anesthesia at brain temp of __ degrees C

A

20

59
Q

What are methods of preventing heat loss? (5)

A

Blankets, forced air warming devices, heated humidification of inhaled gases, warming IV and irrigation fluids, raising ambient temperature

60
Q

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

A

4; 26; 68; 0.25; 40

61
Q

What is the most effective noninvasive means of heat conservation?

A

Forced air warming devices; rewarms at 2.5 degrees C/hr

62
Q

Cutaneous heat loss from extremities makes up __%; thorax/abdomen __%; head __%; respiratory tract __%

A

60; 20; 10; 10

63
Q

A single layer of blankets reduces heat loss by __%

A

30

64
Q

________ induction causes more core hypothermia than _________ induction due to vasodilation.

A

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
Q

Benefits to hypothermia (3)

A

Substantial cerebral and spinal cord protection against ischemia; malignant hyperthermia decreased (in swine); multiple sclerosis patients benefit from hypothermia

66
Q

True/false: Hypothermia is merely a patient comfort issue and does not increase hospital expenses.

A

FALSE!! Delayed anesthesia recovery+ prolonged hospital stay + adverse outcomes can cost >$3065/patient compared to $16 to use convection and IV fluid warmers.

67
Q

Where can we monitor core temperature?

A

Nasopharyngeal, tympanic, PA catheter, eseophageal (lower 1/3 esophagus)

68
Q

Where can we monitor intermediate temperature?

A

Rectal, bladder, axillary

NUNA 690 - Principles (5 decks)

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