Topic 5 - Hypothermia: physiology /clinical use Flashcards Preview

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Flashcards in Topic 5 - Hypothermia: physiology /clinical use Deck (76):
1

Hypothalamus regulates -

vascular regulation
skeletal muscle activity

2

Hypothermia activates the Endocrine system's -- (2)

metabolic regulation
stress response

3

Hypothalmus senses cold where and causes?

sensed by thermoreceptors in the skin
-causes hypothalamus to trigger sympathetic nervous system
-vasoconstriction of skin vessels (to decrease heat loss)
-vasodialtion of skeletal muscular beds (to produce heat when tensing shivering)

4

Can you shiver when you are paralyzed?

NO

5

Endocrine System increases what? (4)

Increases: Oxygen consumption, HR, CO, and BP

6

Temp range
- Mild hypothermia

32-35 C

7

Temp range
- Moderate hypothermia

28-31 C

8

Temp range
- Deep hypothermia

18-27 C

9

Temp range
- Profound hypothermia

<18 C

10

Hypothermia mechanism of protection (3)

-reduction in metabolic rate and oxygen consumption (esp enzymatic reactions)
-preservation of high-energy phosphate stores(use less=more availability)
-reduction of excitatory neurotransmitter release due to ischemia(CNS protection)

11

The safe period of hypothermic CPB is ____ then the period predicted on the basis of __ ___ activity alone.

longer
reduced metabolic activity

12

reduction of excitatory neurotransmitter release due to ischemia - how?

-glutamate accumulation opens Ca channels and activated multiple destructive enzymatic systems
-important in CNS protection

13

general effects of hypothermia (4)

-allow lower pump flows
-better myocardial protection
-less blood trauma (bc low flow/low damage)
-better overall organ protection

14

% of platelets are toast when you go on bypass?

70%

15

Cardiac Index on:
- 34-37 C

2.4 L/min/m2

16

Cardiac Index on:
- 30-34 C

2.0 L/min/m2

17

Cardiac Index on:
- 25-30 C

1.8 L/min/m2

18

Cardiac Index on:
- 20-18 C

1.5 L/min/m2

19

Cardiac Index on:
- <18 C

1.0 L/min/m2

20

DHCA - deep(profound) hypothermia with circ arrest

-repair complex congenital heart defects - small infants and children
- operations involving aortic arch
- operations where maintenance of venous drainage is difficult

21

If arrest period longer than 60 minutes

-use intermittent arrest with brief periods of hypothermic flow
- low-flow hypothermic perfusion is safer than total arrest

22

physiology of hypothermia

- biochemical

metabolic regulation

23

physiology of hypothermia

- chemical

acid-base regulation

24

As temperature decreases ---- biochemical reactions do what?

ALL reaction decrease in rate
decrease: Metabolic (producing & utilizing)
Humoral and coagulation cascades
Cellular maintenance of cell funct

25

Cold = diminished .....

diminished neurotransmission, receptor function ad protein activity

26

the cold effect is ____ with CPB

GLOBAL

27

Q10 principle

relates an increase or decrease in reaction rates to a change in 10C
a unitless quantity

ex Q10=2 a decrease in temp 10C will result in a 50% in reaction rates

28

Normal Q10 range?

are 1.9-4.2

29

oxygen consumption is a ---

reaction

30

Q10 - temperature

in C
the factor by which a rate changes and is a useful way to express the temp dependence of a process

31

7C Principle

Reduction in Oxygen Consumption (VO2)

Every 7C drop in temperature will result in a 50% decease in oxygen consumption

32

from 37 to 30C what % decrease in Oxygen consumption?

50% decrease in oxygen consumption
"moderate"

33

37 to 23 C what % decrease in Oxygen consumption?

75% decrease in Oxygen consumption
"deep"

34

2nd Principle (Q7) - Reduction in metabolic rate

Oxygen demand is reduced 50% for every 7 C drop in temperature

ex @30C VO2=50% normal

35

2nd Principle (Q7) - Reduction in metabolic rate adjuncts ?

anesthesia (give cerebral vascular protection drugs, relaxants)

36

Gas solubility is ____ related to temperature

inversely

37

gas content in solution =

partial pressure of gas x solubility

38

decrease temp what happens to:
solubility?
partial pressure?
total content?

-solubility increases which increase the amount dissolved
-Partial pressure decreases which decreases the amount dissolved
-total content does not change

39

pH responds to changes in?

CO2 content

NOT changes in the CO@ components

40

How does temp affect O2/CO2 content?

Temp does not change O2 or CO2 content -- just the prop of the components (dissolved vs partial)

41

Henry's Law

-- As pressure increases, solubility of gasses in liquids increase (more pressure = more gas can be dissolved in a liquid)
-As temperature increases, solubility of gasses in liquids decreases (warm liquid gas starts to come out of solution)

42

Henrys Law equation?

Content = Partial pressure x Solubility

43

Temperature is ____ related to partial pressure

DIRECTLY

44

Temperature is ___ related to solubility

INVERSELY

45

At a constant temp, the amount of a given gas that dissolves in a given type and volume of liquid is directly prop to the _____ of that gas in equilibrium with that liquid

partial pressure

46

Increase temp:
Solubility?
pO2 & pCO2?

Decrease solubility
increase pO2 & pCO2 (no change in content)

47

decreased temp:
Solubility?
pO2 & pCO2?

Increase solubility
Decreased pO2 & pCO2

48

Concerns with Profound Hypothermia? (2)

Homogeneity of cooling and warming

49

Homogeneity of cooling

rate of cooling
temperature gradients

-- concern with profound hypothermia

50

recommended rate of cooling?

1 C per min

51

recommended rate of warming

1 C per 3 to 5 minutes

52

Consequence of cooling/warming too fast? (3)

- development of temperature gradients w/in tissues
-body cooling after bypass
-exposure to hypothermia

53

Limitation of rate of cooling/warming? (3)

-water temp of heat exchanger
-bld pressure and SVR
-flow rate

54

Temp gradients - max for adults and peds?

reduces probability of GME generation
limit temp gradient btwn arterial and venous blood
- adults <8 C

55

Reduces probability of GME generation
- arterial PO2 mmHg

keep arterial pO2 <200mmhg

when coming off bypass have a smaller gradient

56

HYPERTHERMIA - how does it happen?

Time pressure of rewarming
efficiency of HE
high water temps
perfusion inattention

Risk cerebral injury

57

Techniques of hypothermic bypass (3)

DHCA
HLFB
HILFB (hypothermic intermittent low flow bypass)

58

DHCA - cool to?

to 18-20 C
can turn off pump for 30-60 minutes

59

During DHCA what organ is at greatest risk?

Brain function, developmental capacity and IQ

60

Safe Circ Arrest times @ 37 C:
O2 consumption?
safe arrest time?

100%
4-5 minutes

61

Safe Circ Arrest times @ 29 C:
O2 consumption?
safe arrest time?

50%
8-10 min

62

Safe Circ Arrest times @ 22 C:
O2 consumption?
safe arrest time?

25%
16-20 min "deep"

63

Safe Circ Arrest times @ 16 C:
O2 consumption?
safe arrest time?

12%
32-40min "profound"

64

Safe Circ Arrest times @ 10 C:
O2 consumption?
safe arrest time?

6%
64-80min

65

Standard safe circ arrest temperature ?

18 C

66

Disadvantages of DHCA (4)

Neurologic injury and morbidity
Brain is at the most risk
>60 min arrest is detrimental
>40 min increases risk

67

Advantages to DHCA (4)

-exposure
-reduces metabolic rate and molecular movement
-allows cessation of circulation
-excitatory neurotransmitter reduction

68

DHCA >40 minutes

increases risk

69

DHCA <60min

arrest is detrimental

70

HLFB and HILFB (intermittant low flow bypass) patients demonstrated __ __ of neural dsyfunction in patient

lowered rate compared to DHCA

71

can combine HILFB and DHCA for __ mins every __ min

1-2 mins every 15-20 mins

72

Increase tolerance of brain to ischemic insult - meds(2)

Thiopental
Solumedral

73

Thiopental

short acting barbituate

Increase tolerance of brain to ischemic insult

74

Solumedral

anti-inflammatory, stabilize cell membranes

Increase tolerance of brain to ischemic insult

75

Homogenous Temp (4)

rate of cooling/warming
hemodilution
acid-base management
head in ice

76

Recovery - reperfusion conditions

perfusate temp
perfusate composition: mannitol, bicarbonate, others...