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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
what happens to cardiac output in cardiogenic shock?
low
26
treatment of cardiogenic shock
``` PCI thrombolysis DVVC pacing drugs surgery ```
27
pathology of hypovolaemic shock
haemorrhage dehydration burns
28
what is the problem in hypovolaemic shock?
preload
29
what happens to preload in hypovolaemic shock?
low
30
what happens to SVR in hypovolaemic shock?
high
31
what happens to cardiac output in hypovolaemic shock?
low
32
treatment for hypovolaemic shock
control PRCs fluids burns centre
33
pathology in obstructive shock?
PE tamponade tension pneumothorax
34
what is the problem in obstructive shock?
afterload and preload
35
what happens to preload in obstructive shock?
high
36
what happens to SVR in obstructive shock?
high
37
what happens to cardiac output in obstructive shock?
low
38
pathology of distributive shock
septic | anaphylactic
39
problem in distributive shock
SVR
40
what happens to preload in distributive shock?
normal/low
41
what happens to SVR in distributive shock?
low
42
what happens to cardiac output in distributive shock
high
43
treatment of obstructive shock
thrombolysis surgery pericardiocentesis decompression
44
treatment of distributive shock
sepsis 6 and source control and noradrenaline | adrenaline and source control
45
why measure blood flow?
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
what affects stroke volume?
preload contractility afterload
47
what drugs affect systemic vascular resistance?
vasopressors
48
what intervention affect heart rate?
electricity | drugs
49
what interventions affect preload?
fluid | offload
50
what drugs affect contractility
inotropes
51
what drugs affect afterload?
vasodilators
52
how to measure cardiac output?
methods vary in how invasive they are echocardiography oesophageal doppler dilutional techniques
53
echocardiography
measure aorta diameter and heart rate and stroke volume to calculate cardiac output
54
oesophageal doppler
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
dilutional techniques
based on steward hamilton principle inject dye upstream rate of change on concentration downstream is related to rate of flow
56
normal aortic pressure
100-140/60-90
57
normal left atrial pressure
2-12
58
normal left ventricular pressure
100-140/2-12
59
normal right ventricular pressure
25/2-6
60
normal right atrial pressure
2-6
61
normal pulmonary artery pressure
25/8-12
62
normal pulmonary artery wedge pressure
8-12
63
signs of inadequate cardiac output
examine kidney, brain and skin urine output will decrease consciousness will reduce, altered mental status and agitation capillary refill with lengthen
64
how to monitor urine output?
insert catheter - if worried about organ perfusion
65
how does the body defend BP?
baroreceptors in carotid body and aortic arch
66
what does BP tell us about cardiac output and tissue perfusion?
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
what does hypotension suggest?
patient cannot maintain normal BP while cardiac output is falling so patient has run out of physiological reserve
68
what is the dicrotic notch?
small and brief increase in arterial BP that appears when the aortic valve closes
69
JVP/CVP
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
assessing sympathetic tone
presence of sweating, tachycardia or core-peripheral temperature difference sympathetic overdrive = how hard they need to work to maintain BP
71
Mottling
don't ignore | can indicate prognosis is about to worsen!
72
warm big toes
temperature of big toe correlates with cardiac output | can suggest prognosis
73
cold big toe
peripheral vasoconstriction and rising lactate
74
Lab tests in assessing cardiac output and blood flow
lactate | central venous saturation
75
lactate
over 4mmol/L = 40% mortality
76
raised lactate
needs intervention
77
when is lactate raised?
conditions of low oxygen delivery | produced in anaerobic metabolism
78
central venous saturation
saturation of blood returning to heart | surrogate marker for OER and adequacy of oxygen delivery
79
central venous saturation and cardiac output
falling central venous saturation could indicate poor cardiac output
80
what does low central venous saturation suggest?
demand is greater than supply
81
what does high central venous saturation suggest?
not necessarily reassuring | may imply failure of oxygen delivery to metabolically active capillary beds so oxygen is not removed from the blood
82
what happens in a septic patient?
``` 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
what can restore flow to tissues in sepsis?
nitrate as it dilates capillaries
84
exact cardiac output
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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