Topic 5 - Hypothermia: physiology /clinical use Flashcards
(76 cards)
1
Q
Hypothalamus regulates -
A
vascular regulation
skeletal muscle activity
2
Q
Hypothermia activates the Endocrine system’s – (2)
A
metabolic regulation
stress response
3
Q
Hypothalmus senses cold where and causes?
A
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
Q
Can you shiver when you are paralyzed?
A
NO
5
Q
Endocrine System increases what? (4)
A
Increases: Oxygen consumption, HR, CO, and BP
6
Q
Temp range
- Mild hypothermia
A
32-35 C
7
Q
Temp range
- Moderate hypothermia
A
28-31 C
8
Q
Temp range
- Deep hypothermia
A
18-27 C
9
Q
Temp range
- Profound hypothermia
A
<18 C
10
Q
Hypothermia mechanism of protection (3)
A
- 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
Q
The safe period of hypothermic CPB is ____ then the period predicted on the basis of __ ___ activity alone.
A
longer
reduced metabolic activity
12
Q
reduction of excitatory neurotransmitter release due to ischemia - how?
A
- glutamate accumulation opens Ca channels and activated multiple destructive enzymatic systems
- important in CNS protection
13
Q
general effects of hypothermia (4)
A
- allow lower pump flows
- better myocardial protection
- less blood trauma (bc low flow/low damage)
- better overall organ protection
14
Q
% of platelets are toast when you go on bypass?
A
70%
15
Q
Cardiac Index on:
- 34-37 C
A
2.4 L/min/m2
16
Q
Cardiac Index on:
- 30-34 C
A
2.0 L/min/m2
17
Q
Cardiac Index on:
- 25-30 C
A
1.8 L/min/m2
18
Q
Cardiac Index on:
- 20-18 C
A
1.5 L/min/m2
19
Q
Cardiac Index on:
- <18 C
A
1.0 L/min/m2
20
Q
DHCA - deep(profound) hypothermia with circ arrest
A
- repair complex congenital heart defects - small infants and children
- operations involving aortic arch
- operations where maintenance of venous drainage is difficult
21
Q
If arrest period longer than 60 minutes
A
- use intermittent arrest with brief periods of hypothermic flow
- low-flow hypothermic perfusion is safer than total arrest
22
Q
physiology of hypothermia
- biochemical
A
metabolic regulation
23
Q
physiology of hypothermia
- chemical
A
acid-base regulation
24
Q
As temperature decreases —- biochemical reactions do what?
A
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...
