Lect 14 - Ischaemia, Infarction & Shock

Question 1

What is hypoxia?

Answer 1

Any state of reduced tissue oxygen availability

this can be generalised - whole body e.g. altitude, anaemia

or regional - specific tissues affected

Question 2

what is Ischaemia

Answer 2

Pathological reduction in blood flow to tissues

Usually as a result of obstruction to arterial flow

commonly as a result of thrombosis / embolism

Ischaemia results in tissue hypoxia

Question 3

what is infarction

Answer 3

Ischaemic necrosis caused by occlusion of the arterial supply or venous drainage

Question 4

Give some causes of infarction that are not caused by blood clots

Answer 4

Vasospam
Atheroma expansion
Extrinsic compression (e.g. tumour)
Twisting of vessel roots (e.g. volvulus)
Rupture of vascular supply (e.g. AAA)

Question 5

what are the types of infaction?

Answer 5

Red infarction (haemorrhagic)
White infarction (anaemic)

Question 6

what shape are infarcts?

Answer 6

Most infarcts are wedge-shaped

Obstruction usually occurs at an upstream point, everything downstream is affected.

Question 7

what would you expect to see histologically in infarction?

Answer 7

Coagulative necrosis (Colliquative) in the brain

Question 8

what 4 factors influence the degree of ischaemic damage

Answer 8

Nature of the blood supply

Rate of occlusion

Tissue vulnerability to hypoxia

Blood oxygen content

Question 9

give examples of areas which are less prone to ischaemic damage due to nature of blood supply

Answer 9

Lungs (pulmonary and bronchial arteries)
Liver (hepatic artery and portal vein)
Hand (radial and ulnar artery)

Question 10

why does a quick rate of occlusion make ischaemic damage worse?

Answer 10

doesn’t allow time for the development of alternative (collateral) perfusion pathways

Question 11

what tissues are the most vulnerable to lack of oxygen?

Answer 11

The brain

(irreversible cell damage in 3 to 4 minutes)

The heart

(Mycocyte death in 20 to 30 minutes)

Question 12

what is the leading cause of death in men and women in the West

Answer 12

Ischaemic heart disease

Question 13

give 2 causes of ischaemic stroke

Answer 13

Thrombosis secondary to atherosclerosis

Embolism (e.g. mural thrombus)

Question 14

give 2 Causes of a haemorrhagic stroke

Answer 14

Intracerebral haemorrhage (hypertensive)

Ruptured aneurysm in the circle of Willis (subarachnoid

Question 15

What disease presents with abdominal pain and is caused by the same pathological process as Ischaemic heart disease

Answer 15

Ischaemic bowel disease

Question 16

what does limb ischaemia lead to?

Answer 16

Gangrene

Question 17

what types of Gangrene are there?

Answer 17

Dry gangrene (Ischaemic coagulative necrosis only)

Wet gangrene (Superimposed infection)

Gas gangrene (Superimposed infection with gas producing organism)

Question 18

define gangrene

Answer 18

Infarction of entire portion of limb (or organ)

Question 19

define shock

Answer 19

A physiological state characterised by a significant reduction of systemic tissue perfusion (severe hypotension) resulting in decreased oxygen delivery to the tissues.

Question 20

what does shock lead to?

Answer 20

cellular hypoxia and derangement of critical biochemical processes at first cellular and eventually systemic levels.

Question 21

give some Cellular effects 
of shock (5)

Answer 21

Membrane ion pump dysfunction
Intracellular swelling
Leakage of intracellular contents into the extracellular space
Inadequate regulation of intracellular pH
Anerobic respiration ( makes lactic acid)

Question 22

give some Systemic effects of shock (4)

Answer 22

acidaemia
vascular leakage
Stimulation of inflammatory and anti-inflammatory cascades
End-organ damage

Question 23

after shock becomes irreversible, what sequence of events leads to death?

Answer 23

Cell death
End-organ damage
Multi-organ failure
Death

Question 24

what is Hypovolaemic shock?

Answer 24

Intra-vascular fluid loss.

less preload therefore less cardiac output.

Question 25

what Causes hypovolaemic shock

Answer 25

Haemorrhage, Diarrhoea, vomiting, heat stroke, burns

Question 26

what is Cardiogenic shock

Answer 26

Cardiac pump failure

Question 27

what are the Categories of cardiogenic shock

Answer 27

Myopathic (heart muscle failure) Arrythmia-related (abnormal electrical activity) Mechanical Extra-cardiac (obstruction to blood outflow)

Question 28

what are the casues of myopathic cardiogenic shock

Answer 28

Myocardial infarction Right ventricular infarction Stunned myocardium (following prolonged ischemia)

Question 29

what arrhythmias cause cardiogenic shock

Answer 29

Atrial and ventricular arrhythmias (fibrillation / flutter ) also Ventricular tachycardia, bradyarrhythmias, and complete heart block

Question 30

give some causes of Extra-cardiac cardiogenic shock

Answer 30

Anything that impairs cardiac filling or ejection of blood from heart Massive pulmonary embolism tension pneumothorax Severe constrictive pericarditis pericardial tamponade

Question 31

what is Distributive shock?

Answer 31

severe vasodilation that massively lowers systemic vascular resistance.

Question 32

what sub types of Distributive shock are there?

Answer 32

SEPTIC SHOCK ANAPHYLACTIC SHOCK NEUROGENIC SHOCK TOXIC SHOCK SYNDROME

Question 33

what is Septic Shock?

Answer 33

Severe, over-whelming systemic infections. Cytokines and mediators casue the VASODILATION DIC can also cause Ischaemia

Question 34

what is Anaphylactic shock

Answer 34

Severe type I hypersensitivity reaction: Massive mast cell degranulation casues Vasodilation and also respiratory distress. Patients undergo Circulatory collapse.

Question 35

what is Neurogenic shock?

Answer 35

Spinal injury / anesthetic accidents | Loss of sympathetic vascular tone leads to Vasodilation

Question 36

what is Toxic shock syndrome?

Answer 36

S. aureus / S. pyogenes produce exotoxins known as “superantigens” that Do not require processing by antigen-presenting cells. this casues Non-specific binding of class II MHC to T cell receptors - Widespread release of massive amounts of cytokines

Question 37

are there combined types of shock?

Answer 37

Yes. like septic shock with a Primary distributive component/Hypovolemic component/ Cardiogenic component the infection can lead to symptoms which then compound the shock (like diarrhoea)

Question 38

what is the mortality of Cardiogenic shock?

Answer 38

60 – 90% mortality