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EMS > Lecture 10: Ischaemia, Infarction and shock > Flashcards

Lecture 10: Ischaemia, Infarction and shock Flashcards

1
Q

Define ischaemia:

A

the interruption/ disturbance of blood flow to cells, reducing supply of oxygen and metabolites

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2
Q

Define infarction:

A

Tissue necrosis due to ischaemia

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3
Q

Why does reduced oxygen supply lead to infarction?

A

reduced oxygen means less oxidative phosphorylation which means less ATP required for cell function

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4
Q

What is the effect of cells switching to anaerobic respiration on lactate levels?

A

lactate levels increase

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5
Q

What is the effect of cells switching to anaerobic respiration on lactate levels?

A

lactate levels increase

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6
Q

Give four consequences of a lack of ATP in cells:

A

1) Na+ pumps stop working, causing an accumulation of Na+

2) the plasma membrane is damaged causing leakage of proteins

3) Ca2+ pump stops, causing an influx of Ca2+ into the cell

4) protein synthesis halts

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7
Q

Give two chemical markers for ischaemia that can be found in blood:

A

1) increased lactate

2) leakage of intracellular proteins

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8
Q

Give two examples of intracellular proteins that if found in the blood, indicate cardiac muscle damage:

A

1) creatine kinase

2) troponins

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9
Q

Give two examples of intracellular proteins that if found in the blood, indicate liver damage:

A

1) transaminases

2) alkaline phosphate

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10
Q

Give 6 causes of ischaemia:

A

1) vascular occlusion

2) vasospasm

3) vascular damage

4) extrinsic compression

5) mechanical interruption

6) hypoperfusion

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11
Q

What is the most common of ischaemia?

A

vascular occlusion

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12
Q

Give 4 structures that can lead to occlude blood vessels:

A

1) severe atherosclerosis

2) thrombosis

3) embolism

4) hyper-viscous blood

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13
Q

What is vasospasm?

A

sudden constriction of a blood vessel, reducing its diameter and flow rate

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14
Q

How can vascular damage lead to ischaemia? (2)

A

1) a rupture in a vessel reduces flow to tissues

2) vasculitis can cause inflammation, also reducing flow

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15
Q

Give an example of a structure that could cause extrinsic compression to a vessel:

A

Tumour

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16
Q

Give three examples of mechanical interruptions that cause ischaemia:

A

1) volvulus

2) torsion of a blood vessel

3) intussusception

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17
Q

What is volvulus?

A

twisting of the bowel, leading to ischaemia

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18
Q

What is intussusception?

A

where the intestine folds into a section next to it

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19
Q

Give two causes of hypoperfusion:

A

1) cardiac failure

2) cardiac malformation

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20
Q

Give two complications caused by arterial ischaemia:

A

1) myocardial infarction

2) stroke

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21
Q

Give an example of a complication caused by venous ischaemia:

A

pulmonary embolism

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22
Q

Give two examples of complications caused by capillary ischaemia:

A

1) frostbite

2) disseminated intravascular coagulation

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23
Q

What is disseminated intravascular coagulation (DIC)?

A

a condition in which clots form in numerous small vessels around the body

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24
Q

Give 5 factors that affect the outcomes of ischaemia?

A

1) the nature of the blood supply

2) duration of the ischaemia

3) rate of vascular occlusion

4) tissue vulnerability

5) blood oxygen content

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25
Q

Describe how the nature of blood supply can affect the outcomes of ischaemia:

A

tissues with a dual vascular supply are generally resistant to infarction to a single vessel

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26
Q

Give three examples of organs with dual blood supplies:

A

1) lungs

2) liver

2) hand

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27
Q

Give the dual blood supply of the lungs:

A

pulmonary and bronchial arteries

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28
Q

Give the dual blood supply of the liver:

A

hepatic and portal arteries

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29
Q

Give the dual blood supply of the hand:

A

radial and ulnar arteries

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30
Q

What is the term used to describe circulations where there is just a single artery supplying blood?

A

end arterial circulation

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31
Q

Give 3 examples of that have end arterial circulations:

A

1) kidneys

2) spleen

3) testes

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32
Q

Describe how the duration of ischaemia can affect the outcome of ischaemia:

A

prolonged ischaemia can lead to irreversible necrosis while limited ischaemia leads to reversible ischaemic injury

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33
Q

Describe how the rate of vascular occlusion can affect the outcome of ischaemia:

A

slow developing occlusions are less likely to cause infarction in tissues as the slow development allows for the development of alternative perfusion pathways

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34
Q

What is a term to used alternative blood supplies to tissues?

A

collateral circulation

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35
Q

Describe how tissue vulnerability can affect the outcome of ischaemia:

A

certain tissues like the brain are more sensitive to ischaemia as it is more metabolically active

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36
Q

How long does it take for ischaemia to cause irreversible damage in the brain?

A

3-4 minutes

37
Q

How long does it take for ischaemia to cause irreversible damage in the heart?

A

20-30 minutes

38
Q

Describe how blood oxygen content can affect the outcome of ischaemia:

A

reduced oxygen in the blood e.g. from anaemia makes individuals more vulnerable to infarction

39
Q

What are the two types of infarcts?

A

1) coagulative

2) liquefactive

40
Q

What cell process creates a coagulative infarct?

A

denaturation of cells where enzymes become unable to break down the cell structure

41
Q

How does a coagulative infarct appear under a microscope?

A

the basic outlines of cells are preserved but it appears pale and lacks content (ghost cell)

42
Q

Are necrotic tissues firm or soft in coagulative infarcts?

A

firm

43
Q

What colour are coagulative infarcts?

A

white

44
Q

What cell process creates liquefactive infarcts?

A

enzyme digestion

45
Q

In which tissue are liquefactive infarcts formed?

A

brain

46
Q

Describe a liquefactive infarct:

A

cells are completely digested and broken down into a mushy mess until it is liquefied, creating a cavity of cyst in the brain

47
Q

What makes some infarcts white?

A

the blood is trapped in the infarct, denaturing, causing it to lose its red colour

48
Q

What makes some infarcts red?

A

fresh blood is still able to enter the infarcted area

49
Q

In which type of circulation supply are red infarcts created?

A

dual blood supply

50
Q

In which type of circulation supply are white infarcts created?

A

single blood supply

51
Q

What shape are most infarcts?

A

wedge-shaped

52
Q

Why are most infarcts wedge-shaped?

A

because obstructions often occur at proximal vessels of a tissue affecting the entire downstream fan-shaped network of vessels

53
Q

What gross and microscopic features can be seen in an infarct after 0-4 hours?

A

no gross or microscopic changes

54
Q

What gross and microscopic features can be seen in an infarct after 4-24 hours?

A

1) gross: dark mottling

2) microscopic: oedema, haemorrhage

55
Q

What gross and microscopic features can be seen in an infarct after 1-3 days?

A

1) gross: yellow colour with haemorrhagic edge

2) microscopic: oedema with early neutrophil infiltration

56
Q

What gross and microscopic features can be seen in an infarct after 3-7 days?

A

1) gross: yellow centre will become soft

2) microscopic: dying neutrophils with macrophage infiltration can be seen

57
Q

What gross and microscopic features can be seen in an infarct after 1-2 weeks?

A

1) gross: a grey-red colour can be seen on the organ

2) microscopic: granulation tissue formation can be seen and recruitment of fibroblasts for collagen production

58
Q

What gross and microscopic features can be seen in an infarct after 2-8 weeks?

A

1) gross: a fibrous scar can be seen on the organ

2) microscopic: increased collagen can be seen

59
Q

Why is the heart at risk of rupture following acute myocardial ischaemia?

A

the heart tissue is weakened

60
Q

Why is the heart at risk of heart failure following acute myocardial ischaemia?

A

the scarred tissue is non-functional

61
Q

What four factors cause reperfusion injury?

A

1) free radical damage

2) cytokine recruitment of inflammatory cells

3) activation of the compliment pathway

4) build-up of Ca2+ ions

62
Q

Why is it that ischaemic tissue is susceptible to free radical damage?

A

healthy cells use antioxidants to control free radical formation but damaged cells have less of these

63
Q

Define shock:

A

a pathophysiological state of reduced systemic tissue perfusion (generalised tissue effect) due to cardiovascular collapse

64
Q

What is the key factor in causing shock?

A

reduced mean arterial pressure

65
Q

What two factors determine mean arterial pressure?

A

1) cardiac output

2) total peripheral resistance

66
Q

What two factors determine mean arterial pressure?

A

1) cardiac output

2) total peripheral resistance

67
Q

What factors can contribute to shock? (2)

A

1) any factors that affect cardiac output (heart rate and stroke volume)

2) any factors that affect peripheral resistance (arteriolar radius)

68
Q

Give the three broad types of shock:

A

three broad types of shock:
1) hypovolaemic

2) cardiogenic

3) distributive

69
Q

What is hypovolaemic shock?

A

intra-vascular fluid loss causing reduced pre-load/ venous return to the heart, reducing blood pressure

70
Q

What are three key presentations associated with hypovolaemic shock?

A

1) tachycardia

2) pallor

3) cool skin (due to vital organs being prioritised)

71
Q

True or false: an individual in hypovolaemic shock may present with a normal blood pressure due to compensation

A

True

72
Q

Give 5 haemorrhagic causes of hypovolaemic shock:

A

1) trauma

2) gastrointestinal bleeding

3) haemorrhagic pancreatitis

4) fractures

5) ruptures in vessels

73
Q

Give 5 non-haemorrhagic causes of hypovolaemic shock:

A

1) diarrhoea

2) heat stroke

3) burns

4) vomiting

5) third spacing

74
Q

What is third spacing?

A

When fluid accumulates in a portion of the body

75
Q

What is cardiogenic shock?

A

cardiac pump failure meaning a healthy blood pressure cannot be maintained

76
Q

What are the four types of cardiogenic shock?

A

1) myopathic

2) arrhythmia

3) mechanical

4) extracardiac

77
Q

What is myopathic-related cardiogenic shock?

A

heart muscle failure due to cardiomyopathies and myocardial infarctions causing reduced blood pressure and shock

78
Q

What is arrhythmia-related cardiogenic shock?

A

electrical abnormalities or atrial or ventricular arrhythmias e.g. fibrillation not allowing enough blood to fill the heart, causing reduced blood pressure and shock

79
Q

What is mechanical-related cardiogenic shock?

A

defects relating to blood flow in the heart causing reduced cardiac output and blood pressure and thus shock

80
Q

Give three mechanical defects that can lead to cardiogenic shock:

A

1) valvular defects

2) ventricular septal defects

3) atrial myxoma

81
Q

What is an atrial myxoma?

A

a non-cancerous tumour of the heart

82
Q

What is extracardiac cardiogenic shock?

A

anything outside of the heart impairing cardiac filling or ejection, causing reduced blood pressure and shock

83
Q

Give 3 extracardiac changes that can cause cardiogenic shock:

A

1) massive pulmonary embolism

2) tension pneumothorax

3) pericardial tamponade

84
Q

What is pericardial tamponade?

A

Fluid accumulating around the heart, slowly stops the heart from contracting

85
Q

What is distributive shock?

A

reduced systemic vascular resistance due to severe vasodilatation

86
Q

Give four types of distributive shock:

A

1) septic

2) anaphylactic

3) neurogenic

4) toxic shock

87
Q

Describe the heartbeat in a patient suffering distributive shock:

A

bounding heartbeat

88
Q

True or false: a patient can have mixed shock (a combination of 2 or 3 different types of shock

A

True

EMS (54 decks)

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