Shock (or cardiovascular collapse) is the ter given to any process that results in reduced blood flow through microcirculatory beds. Regardless of the underlying pathology, shock gives rise to systemic hypoperfusion caused by reduction either in CO or in the effective circulating blood volume.
This causes hypotension, followed by impaired tissue perfusion and cellular hypoxia. Multiple organ failure results with death or significant tissue and organ damage as the sequelae.
Classification of shock
Major causes of shock
- Cardiogenic shock
- Hypovolaemic shock
- Septic shock
Less common causes of shock
- Neurogenic shock
- Anaphylactic shock
Mechanisms of cardiogenic shock
Failure of the myyocardial pump owing to intrinic myocardial damage, extrinsic pressure, or obstruction to outflow.
Causes of cardiogenic shock
- Ventricular rupture
- Cardiac tamponade
- Pulmonary embolism
Mechanisms of hypovolaemic shock
Inadequate blood or plasma volume
Causes of hypovolaemic shock
Fluid loss e.g. vomiting, diarrhoea burns or trauma, haemorrhage
Mechanisms of septic shock
Overwhelming microbial infection activates cytokine cascades (TNF, IL-1 and IL-6) which cause systemic vasodilaton, hypotension, widespread endothelial damage (DIC and ARDS) ad reduced myocardiac contractility.
Causes of septic shock
Endotoxic shock (caused by LPS toxin from GN organisms), gram positive septicaemia, fungal sepsis, superantigens (e.g. TSS).
Spinal injury ot neurotoxin/anaesthic agent that causes loss of vascular tone and subsequent pooling of blood in the venous system with relative hypovolaemia in the arterial system.
IgE-mediated hypersensitivity response (type 1) is associated with systemic vasodilation and increased vascular permeability. Pooling of blood and relative hypovolaemia results.