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2nd year > Clinical measurement of blood flow > Flashcards

Clinical measurement of blood flow Flashcards

1
Q

purpose of circulation

A

to deliver oxygen

DO2

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2
Q

how is DO2 measured?

A

mlO2/min

depends on blood flow (L/min) and oxygen concentration (mlO2/L)

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3
Q

how much O2 does a healthy adult consume at rest?

A

200-250mL/min O2

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4
Q

OER

A

oxygen extraction ratio

each organ has their own value

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5
Q

when does OER change

A

if DO2 falls OER increases to compensate

when OER is maximised delivery of oxygen becomes supply-dependant

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6
Q

what is shock?

A

inadequate organ perfusion, due to acute failure of circulation to meet metabolic demands of tissues, often characterised by hypotension

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7
Q

what is preload?

A

filling
end diastolic volume
how much blood is delivered to the heart before it contracts

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8
Q

starlings law

A

force of contraction is proportional to initial myocardial fibre length
end diastolic stretch of myocardial fibres

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9
Q

compliance

A

determines the relationship between left ventricular end diastolic volume and left ventricular end diastolic pressure
isn’t constant

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10
Q

measuring compliance

A

use paired measurements to see where on ventricular compliance curve the preload is

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11
Q

JVP and CVP

A

can be used to measure preload but not accurate because pressure doesn’t equal volume because of compliance

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12
Q

what is contractility?

A

how well the heart contracts
intrinsic myocardial function
inotropic state
difficult to measure

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13
Q

calculate contractility

A

dP/dt

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14
Q

what is afterload?

A

load against which the heart must eject blood

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15
Q

what affects afterload?

A 
LV diameter 
ventricular wall thickness 
ventricular wall stiffness 
aortic elastance
aortic diastolic BP 
aortic valve pathology
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16
Q

What is systemic vascular resistance?

A

resistance of arterial circulation

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17
Q

what determines systemic vascular resistance?

A

arteriolar tone - vasoconstriction and vasodilation

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18
Q

what affects systemic vascular resistance?

A

autonomic nervous system

drugs

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19
Q

what drugs affect systemic vascular resistance?

A

nitrates

adrenaline

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20
Q

afterload
preload
SVR

A

they are all interrelated

decrease in afterload may decrease preload

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21
Q

cardiogenic shock pathology

A

muscle
conduction system
valves

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22
Q

what is the problem in cardiogenic shock?

A

contractility
heart rate
stroke volume

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23
Q

what happens to preload in cardiogenic shock ?

A

high

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24
Q

what happens to SVR in cardiogenic shock?

A

high

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25
Q

what happens to cardiac output in cardiogenic shock?

A

low

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26
Q

treatment of cardiogenic shock

A 
PCI
thrombolysis 
DVVC
pacing
drugs
surgery
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27
Q

pathology of hypovolaemic shock

A

haemorrhage
dehydration
burns

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28
Q

what is the problem in hypovolaemic shock?

A

preload

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29
Q

what happens to preload in hypovolaemic shock?

A

low

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30
Q

what happens to SVR in hypovolaemic shock?

A

high

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31
Q

what happens to cardiac output in hypovolaemic shock?

A

low

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32
Q

treatment for hypovolaemic shock

A

control
PRCs
fluids
burns centre

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33
Q

pathology in obstructive shock?

A

PE
tamponade
tension pneumothorax

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34
Q

what is the problem in obstructive shock?

A

afterload and preload

35
Q

what happens to preload in obstructive shock?

A

high

36
Q

what happens to SVR in obstructive shock?

A

high

37
Q

what happens to cardiac output in obstructive shock?

A

low

38
Q

pathology of distributive shock

A

septic

anaphylactic

39
Q

problem in distributive shock

A

SVR

40
Q

what happens to preload in distributive shock?

A

normal/low

41
Q

what happens to SVR in distributive shock?

A

low

42
Q

what happens to cardiac output in distributive shock

A

high

43
Q

treatment of obstructive shock

A

thrombolysis
surgery
pericardiocentesis
decompression

44
Q

treatment of distributive shock

A

sepsis 6 and source control and noradrenaline

adrenaline and source control

45
Q

why measure blood flow?

A

to identify complex or combination pathology
cause of shock is unclear
titrate therapies
cardiac surgery
monitor transplanted organs - renal artery doppler
assess organs for transplant

46
Q

what affects stroke volume?

A

preload
contractility
afterload

47
Q

what drugs affect systemic vascular resistance?

A

vasopressors

48
Q

what intervention affect heart rate?

A

electricity

drugs

49
Q

what interventions affect preload?

A

fluid

offload

50
Q

what drugs affect contractility

A

inotropes

51
Q

what drugs affect afterload?

A

vasodilators

52
Q

how to measure cardiac output?

A

methods vary in how invasive they are
echocardiography
oesophageal doppler
dilutional techniques

53
Q

echocardiography

A

measure aorta diameter and heart rate and stroke volume to calculate cardiac output

54
Q

oesophageal doppler

A

uses doppler effect to measure speed of blood in descending aorta
estimation of cross-sectional area of aorta
Stroke volume = area x stroke distance

55
Q

dilutional techniques

A

based on steward hamilton principle
inject dye upstream
rate of change on concentration downstream is related to rate of flow

56
Q

normal aortic pressure

A

100-140/60-90

57
Q

normal left atrial pressure

A

2-12

58
Q

normal left ventricular pressure

A

100-140/2-12

59
Q

normal right ventricular pressure

A

25/2-6

60
Q

normal right atrial pressure

A

2-6

61
Q

normal pulmonary artery pressure

A

25/8-12

62
Q

normal pulmonary artery wedge pressure

A

8-12

63
Q

signs of inadequate cardiac output

A

examine kidney, brain and skin
urine output will decrease
consciousness will reduce, altered mental status and agitation
capillary refill with lengthen

64
Q

how to monitor urine output?

A

insert catheter - if worried about organ perfusion

65
Q

how does the body defend BP?

A

baroreceptors in carotid body and aortic arch

66
Q

what does BP tell us about cardiac output and tissue perfusion?

A

nothing
normal BP doesn’t mean normal cardiac output
gives some information about contractility
height of dicrotic notch can give information on volume status

67
Q

what does hypotension suggest?

A

patient cannot maintain normal BP while cardiac output is falling so patient has run out of physiological reserve

68
Q

what is the dicrotic notch?

A

small and brief increase in arterial BP that appears when the aortic valve closes

69
Q

JVP/CVP

A

reflects pressure in right atrium
doesn’t tell much about preload
CVP is poor measure of volume status
change in CVP more useful - paired values to determine location on compliance curve

70
Q

assessing sympathetic tone

A

presence of sweating, tachycardia or core-peripheral temperature difference
sympathetic overdrive = how hard they need to work to maintain BP

71
Q

Mottling

A

don’t ignore

can indicate prognosis is about to worsen!

72
Q

warm big toes

A

temperature of big toe correlates with cardiac output

can suggest prognosis

73
Q

cold big toe

A

peripheral vasoconstriction and rising lactate

74
Q

Lab tests in assessing cardiac output and blood flow

A

lactate

central venous saturation

75
Q

lactate

A

over 4mmol/L = 40% mortality

76
Q

raised lactate

A

needs intervention

77
Q

when is lactate raised?

A

conditions of low oxygen delivery

produced in anaerobic metabolism

78
Q

central venous saturation

A

saturation of blood returning to heart

surrogate marker for OER and adequacy of oxygen delivery

79
Q

central venous saturation and cardiac output

A

falling central venous saturation could indicate poor cardiac output

80
Q

what does low central venous saturation suggest?

A

demand is greater than supply

81
Q

what does high central venous saturation suggest?

A

not necessarily reassuring

may imply failure of oxygen delivery to metabolically active capillary beds so oxygen is not removed from the blood

82
Q

what happens in a septic patient?

A 
vasodilation due to inflammatory mediators causing reduced SVR and so BP falls 
reflexes initiated 
Heart rate increases, contractility increases (tachycardia and hypercontractility)
cardiac output rises 
high CO and vasodilation 
capillary stasis
no oxygen delivery to tissues
capillary density falls
83
Q

what can restore flow to tissues in sepsis?

A

nitrate as it dilates capillaries

84
Q

exact cardiac output

A

more important to assess adequacy of blood flow than knowing the exact cardiac output
cardiac output tells us a little about tissue blood flow and less about oxygen use

2nd year (48 decks)

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