12. Ischaemia, Infarction and Shock Flashcards
what is hypoxia
any state of reduced tissue oxygen availability, can be regional or generalised
what is ischaemia?
pathological reduction in blood flow to tissues
what is infarction?
necrosis of tissue due to ischaemia, by occlusion of arterial supply or venous drainage
what is an infarct?
an area of infarction in tissues
what is the consequence of ischaemia?
hypoxia
is ischaemia reversible or irreversible?
reversible if it lasts for a short period of time, irreversible if it is prolonged
how is reversible ischaemia treated?
therapeutic reperfusion
what is the danger of therapeutic reperfusion?
reperfusion can cause inflammatory cells to generate a reactive oxygen species and this can cause further cell damage (reperfusion injury)
what are the causes of infarction?
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
how can infarction be classified morphologically?
by colour -
red infarction - haemorrhagic, when there is a dual blood supply
white infarction (anaemic) - single blood supply, hence it is totally cut off
what is the shape of infarcts?
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.
what is the histological observation in an infarct?
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
what factors influence the degree of ischaemic damage?
nature of blood supply
rate of occlusion
tissue vulnerability to hypoxia
blood oxygen content
what is shock?
a physiological state characterised by a significant reduction of systemic tissue perfusion (severe hypotension) resulting in decreased oxygen delivery to the tissues
what is the effect of shock on the body?
critical imbalance between oxygen delivery and consumption
cellular hypoxia
derangement of critical biochemical processes at first cellular and eventually at systemic levels
what are the cellular effects of shock?
membrane ion pump dysfunction
intracellular swelling
leakage of intracellular contents into the extracellular space
inadequate regulation of intracellular pH
anaerobic respiration, producing lactic acid
what are the systemic effects of shock?
alterations in serum pH (academia)
endothelial dysfunction and vascular leakage
stimulation of inflammatory and anti-inflammatory cascades
end-organ damage
is shock reversible or irreversible?
initially reversible but rapidly becomes irreversible
what are the consequences of shock, if left untreated?
cell death
end-organ damage
multi-organ failure
death
what are the 3 types of shock?
- hypovolaemic
- cariogenic
- distributive
what is hypovolaemic shock?
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
what are the causes of hypovolaemic shock?
trauma, GI bleeds, fractures, ruptured haematoma, ruptured aneurysm
D&V, heat stroke, burns
third spacing
what is third spacing?
acute loss of fluid into internal body cavities, this is a common complication after surgery, in intestinal obstruction, pancreatitis or cirrhosis
what is cardiogenic shock?
cardiac pump failure, low cardiac output and therefore increased systemic vascular resistance
what are the categories of cariogenic shock?
- myopathic (an infarction)
- arrhythmia-related
- mechanical (valve defects etc.)
- extra cardiac - obstruction to blood outflow
what is distributive shock?
low SVR due to severe vasodilation
what are the subtypes of distributive shock?
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
