Shock
What is shock?
- 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
- Disseminated intravascular coagulation occurs
- Water and electrolyte disturbances occur
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