Hypothermia

Question 1

normal core body temperature is defined as:

Answer 1

37*C

Question 2

Elderly have set-point ______ than normal

Answer 2

0.5*C Lower

Question 3

Hypothermia- oral temp =

Answer 3

<36*C

Question 4

Hyperthermia =
______ am
______ pm

Answer 4

> 37.2*C am

>37.7*C pm

Question 5

what functions as the “control center” for temperature?

Answer 5

hypothalamus

Question 6

what thermoregulatory mechanisms does the body exhibit at temps <37*C?

Answer 6

vasoconstriction followed by shivering

Question 7

what thermoregulatory mechanisms does the body exhibit at temps >37*C

Answer 7

sweating followed by vasodilation

Question 8

what happens to the threshold temperature for thermoregulatory responses under anesthesia?

Answer 8

widens range. Makes it harder for body to regulate

Question 9

How are Mild, Moderate, Severe Hypothermia and DHCA defined?

Answer 9

Mild = 34-36
Moderate = 30-40
Severe = <30
DHCA = 18*C

Question 10

Where can core (trunk & head) body temp be measured?

Answer 10

Pulmonary Artery
Tympanic Membrane
Distal Esophagus
Nasopharynx

Question 11

Name other places to measure temperature

Answer 11

Bladder
Rectum
Skin/Muscle

Question 12

When would Bladder and rectal temperatures not be accurate?

Answer 12

Bladder = poor kidney fxn, irrigation nearby
Rectal = "impaled on turd"

Question 13

how do core and peripheral temps differ in their response to external influences?

Answer 13

Core= varies little with environment
Peripheral = varies significantly over surface

Question 14

how is temperature sensed?

Answer 14

afferent thermal sensing:
Cold= delta A fibers
Hot = C fibers

Question 15

how does the body respond to heat?

Answer 15

sweating and active vasodilation

Question 16

sweating can dissipate ___X the BMR in a dry, windy environment

Answer 16

10

Question 17

when heated, what happens to the temperature gradient?

Answer 17

moves toward peripheral tissues

Question 18

when cooled, what happens to the temperature gradient?

Answer 18

moves towards core

Question 19

how does the body respond to cold? why can it be harmful?

Answer 19

vasoconstriction- moves circulation to core to preserve vital organs.
This can cut off flow to peripheral tissues and cause necrosis

Question 20

what is the most effective thermoregulatory response?

Answer 20

behavior

Question 21

shivering can have what effect on BMR?

Answer 21

increase 2-3x

Question 22

what is non-shivering thermogenesis?

Answer 22

seen in infants - brown fat metabolism

increased SA to body ratio

Question 23

the majority of heat loss to the environment is due to?

Answer 23

radiation

Question 24

radiation is a function of what? This leaves what population particularly susceptible?

Answer 24

BSA

Children

Question 25

what is the second largest route of heat loss?

Answer 25

convection

Question 26

How does convection work and what affects its magnitude?

Answer 26

heat exchange from body to surrounding air/fluid | Magnitude effected by temperature gradient

Question 27

a bair hugger is an example of what form of heat exchange?

Answer 27

convection - per MM and manufacturer website.

Question 28

where are evaporative heat losses most common?

Answer 28

exposed visceral surfaces to environment and burns

Question 29

how can regional anesthesia effect thermoregulation?

Answer 29

affects afferent sensing, so hypothalamus isn't sure what to do

Question 30

during anesthesia, where is the body heat redistributed?

Answer 30

to the periphery (resultant loss of core temp)

Question 31

most patients lose _____ *C in first hour

Answer 31

1-1.5*C

Question 32

what are the phases of cooling?

Answer 32

1. Initial - redistribution (core->preiphery) 2. core temp decrease in first hour (reduced vasoconstriction threshold) 3. linear phase due to heat loss exceeding BMR 4. Plateau when heat loss equals production

Question 33

T or F: Patients usually regain normal temperature by conclusion of surgery

Answer 33

False

Question 34

What effect does temperature have on wound infections and hospital stays?

Answer 34

Increases wound infection rate 3x | Increases hospital stay by 2 days

Question 35

thermoregulatory threshold for shivering is decreased _____ by inhalational anesthetics and nitrous-narcotic techniques

Answer 35

34.5*C

Question 36

thermoregulatory threshold for shivering is decreased _____ by proposal-nitrous techniques

Answer 36

33*C

Question 37

how do the elder compare to the normal population when looking at cooling and warming rates?

Answer 37

cool faster, warm slower

Question 38

what are 3 predictive factors of an increased risk for perioperative hypothermia?

Answer 38

old age short height low pre-op BP

Question 39

what two factors have a greater effect on hypothermia than the duration of surgery, ambient room temperature and percent body fat when using regional anesthesia?

Answer 39

high level of blockade | advanced age

Question 40

What are some possible consequences of hypothermia?

Answer 40

``` -Poor would healing (Impaired immune fxn, decreased O2 to tissue, collagen production) -increased mortality -arrythmias - ischemia and angina - decreased drug metabolism - reduced platelet fxn - decreased activation of clotting - blood loss -prolonged PACU stay - increased O2 consumption ```

Question 41

when is shivering more likely to occur?

Answer 41

when patient is rewarmed faster

Question 42

what effect does shivering have on O2 consumption?

Answer 42

increases

Question 43

what are some potential benefits to hypothermia?

Answer 43

- (1-3*) = protection against cerebral ischemia - more profound = temp-dependent decrease in BMR and CMRO2 - MAY improve outcome in septic ARDS - decreases MAC 5% per *C

Question 44

At what temperatures is brain injury likely vs neuroprotection?

Answer 44

37*C may cause brain injury

Question 45

what effect does temperature have on MAC requirements?

Answer 45

decreases MAC 5% per *C | colder patients require less anesthesia

Question 46

when would you want to induce deliberate hypothermia and why?

Answer 46

CPB for heart or brain surgery - improves tissue tolerance for ischemia - protects against ischemia

Question 47

in what instance would you not want to rewarm tissue?

Answer 47

Ischemic tissue should not be rewarmed (ie tourniquet or AAA cross clamp) -want to keep low BMR in ischemic areas

Question 48

when sampling temperature at multiple sites, which is the first to cool and rewarm?

Answer 48

esophageal

Question 49

temperature gradients are related to…..

Answer 49

differences in tissue blood flow

Question 50

what type of cooling is necessary to decrease O2 consumption for prolonged Circ. Arrest cases?

Answer 50

Uniform cooling

Question 51

what is used as an indicator of cerebral temperature?

Answer 51

nasopharyngeal temperature

Question 52

normothermic bypass patients showed an increased incidence of what adverse event?

Answer 52

stroke

Question 53

what are some methods to prevent hypothermia in the OR?

Answer 53

- warm room, bed, fluids, inspired air | - use warming blankets and keep pt covered