Shock
Acute circulatory failure resulting in inadequate tissue perfusion
- Distributive shock
- Obstructive shock
[Response to reduced circulating volume]
Haemorrhage
- Primary - at time of injury
- Reactionary - within 24hs (due to build up of blood pressure)
- Secondary - Thrombus degradation by infective organisms
Hormonal regulation of fluid volume (important in SHOCK)
- Reduced circulating volume results in reduction of blood pressure
- Detected by carotid sinus/aortic arch baroreceptors: Sympathetic response
- Catecholamine response - vasoconstriction to maintain BP, increase FOC, increase cardiac output
- Stimulation of B2 adrenoceptors in kidneys kicks off RAS response
- Decrease in renal blood flow / renal perfusion pressure: Renin-Angiotensin-Aldosterone response
- B2 stimulation releases renin; converts angiogensinogen to angiotensin I
- angiotensin I converted to angiotensin II by ACE (in the lungs, also degrades bradykinin)
- Angiotensin II potent vasoconstrictor
- Angiotensin II stimulates the release of aldosterone (from zona glomerulosa) which promotes Na/water resorption from DCT
- Stress hormone release - corticosteroids from adrenal cortex
- Salt/water retention
- Increase in plasma osmolarity: ADH (produced in paraventricular and supraoptic nuclei) response
- Osmoreceptors detect a rise in osmolarity (from loss of volume)
- Stimulates the release of vasopressin (aka anti-diuretic hormone) - potent vasoconstrictor
- ADH (via increase cAMP, aquaporin) stimulates resorption of water from DCT/CCD
- Reduced renal perfusion stimulates EPO production (long term)
- Increase in fluid volume
- Distention of cardiac atria - leads to release of ANP: promotes diuresis
- Increase in brain naturetic peptide (BNP increased in "cardiac failure")
Type | Pathology | Features | Managment | |||||||||||||||
Anaphylactic | ||||||||||||||||||
Cardiogenic |
...resulting from myocardial dysfunction
Causes
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Pathophysiology
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Investigations:
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Hypovolaemic shock |
Causes
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Severity of blood loss
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Neurogenic (cf spinal shock) | Loss of sympathetic outflow following spinal cord injury | |||||||||||||||||
Septic | Shock in the presence of sepsis |
Hypoperfusion Hypotension Organ dysfunction |