A pathological condition characterised by inadequate tissue and
oxygen perfusion, which, seriously reduces the delivery of oxygen and
other essential nutrients to a level below that required for normal
cellular activities.
Cellular injury and destruction may occur and tissue and organ
functions deteriorate
There is progressive cardiovascular collapse resulting in:
Hypotension
Hyperventilation
Reduced level of consciousness
Oliguria
Shock has three stages
Compensation
Progression
Irreversibility
Causes
Hypovolaemia
Haemorrhage
Burns
Dehydration
Cardiogenic
Septic shock
Anaphylaxis
Physiology of shock
Compensation
Loss of effective circulating blood volume initiates reactive
changes
Re-distribution of circulating blood volume occurs
Perfusion to coronary and cerebral circulations is maintained by
autoregulation
Acute hypovolaemia results in
Reduced central venous pressure
Reduced cardiac filling and cardiac output
Sympathetic stimulation causes
Reduced splanchnic perfusion
Cutaneous vasoconstriction
Reduced renal perfusion
Venous return is increased
Increases myocardial contractility
Renin / angiotensin system is stimulated
Anti-diuretic hormone is released
Urine output is reduced
If compensation is adequate
Blood pressure is maintained
Oxygen delivery remains adequate
Progression
If compensatory mechanisms are inadequate
Ischaemia and hypoxia occurs
Anaerobic metabolism results in increased lactate production
Capillary permeability increases
Pulmonary oedema may occur resulting in ARDS
Renal hypoperfusion can result in acute tubular necrosis
Irreversibility
If compensatory mechanisms fail
Vasodilatation occurs and capillary permeability is increased
Progressive tissue hypoxia occurs
When systolic pressure falls below 50-60 mmHg
Reduced coronary circulation results in myocardial ischaemia
Cerebral ischaemia causes vasomotor depression and visceral
vasodilatation