12. Ischaemia, Infarction and Shock

Question 1

what is hypoxia

Answer 1

any state of reduced tissue oxygen availability, can be regional or generalised

Question 2

what is ischaemia?

Answer 2

pathological reduction in blood flow to tissues

Question 3

what is infarction?

Answer 3

necrosis of tissue due to ischaemia, by occlusion of arterial supply or venous drainage

Question 4

what is an infarct?

Answer 4

an area of infarction in tissues

Question 5

what is the consequence of ischaemia?

Answer 5

hypoxia

Question 6

is ischaemia reversible or irreversible?

Answer 6

reversible if it lasts for a short period of time, irreversible if it is prolonged

Question 7

how is reversible ischaemia treated?

Answer 7

therapeutic reperfusion

Question 8

what is the danger of therapeutic reperfusion?

Answer 8

reperfusion can cause inflammatory cells to generate a reactive oxygen species and this can cause further cell damage (reperfusion injury)

Question 9

what are the causes of infarction?

Answer 9

thrombosis and embolism
vasospasm
atheroma expansion
extrinsic compression
twisting of vessel roots eg. volvulus  
rupture of vascular supply eg. AAA
steal - when a blood vessel splits and one of the branches is narrowed pathologically. blood follows path of least resistance therefore the narrower branch gets poorer perfusion
 venous occlusion uncommon

Question 10

how can infarction be classified morphologically?

Answer 10

by colour -
red infarction - haemorrhagic, when there is a dual blood supply
white infarction (anaemic) - single blood supply, hence it is totally cut off

Question 11

what is the shape of infarcts?

Answer 11

wedge shaped, because obstruction usually occurs at an upstream point, and the entire downstream ares will be infarcted. the further the tissue is from the blocked supply, the more damage is caused.

Question 12

what is the histological observation in an infarct?

Answer 12

coagulative necrosis (usually)
colliquative necrosis (in the brain)
no change in tissues seen if the person dies suddenly, because there is no time for haemorrhages or an inflammatory response to develop

Question 13

what factors influence the degree of ischaemic damage?

Answer 13

nature of blood supply
rate of occlusion
tissue vulnerability to hypoxia
blood oxygen content

Question 14

what is shock?

Answer 14

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

Question 15

what is the effect of shock on the body?

Answer 15

critical imbalance between oxygen delivery and consumption
cellular hypoxia
derangement of critical biochemical processes at first cellular and eventually at systemic levels

Question 16

what are the cellular effects of shock?

Answer 16

membrane ion pump dysfunction
intracellular swelling
leakage of intracellular contents into the extracellular space
inadequate regulation of intracellular pH
anaerobic respiration, producing lactic acid

Question 17

what are the systemic effects of shock?

Answer 17

alterations in serum pH (academia)
endothelial dysfunction and vascular leakage
stimulation of inflammatory and anti-inflammatory cascades
end-organ damage

Question 18

is shock reversible or irreversible?

Answer 18

initially reversible but rapidly becomes irreversible

Question 19

what are the consequences of shock, if left untreated?

Answer 19

cell death
end-organ damage
multi-organ failure
death

Question 20

what are the 3 types of shock?

Answer 20

1. hypovolaemic
2. cariogenic
3. distributive

Question 21

what is hypovolaemic shock?

Answer 21

loss of fluid leading to low blood volume. amount of blood returning to the heart reduces, so stroke volume decreases.
cardiac output and MAP reduces.
result - vasoconstriction and tachycardia to increase BP (pale and cold)
clammy because this is a sympathetic response
no urine production

Question 22

what are the causes of hypovolaemic shock?

Answer 22

trauma, GI bleeds, fractures, ruptured haematoma, ruptured aneurysm
D&V, heat stroke, burns
third spacing

Question 23

what is third spacing?

Answer 23

acute loss of fluid into internal body cavities, this is a common complication after surgery, in intestinal obstruction, pancreatitis or cirrhosis

Question 24

what is cardiogenic shock?

Answer 24

cardiac pump failure, low cardiac output and therefore increased systemic vascular resistance

Question 25

what are the categories of cariogenic shock?

Answer 25

1. myopathic (an infarction)
2. arrhythmia-related
3. mechanical (valve defects etc.)
4. extra cardiac - obstruction to blood outflow

Question 26

what is distributive shock?

Answer 26

low SVR due to severe vasodilation

Question 27

what are the subtypes of distributive shock?

Answer 27

anaphylactic - type I hypersensitivity
septic - overwhelming sepsis
toxic shock syndrome - release of exotoxins by s. aureus or s. progenies. SEVERE
neurogenic - spinal injury, anaesthetic accidents
others