Shock

Shock – acute circulatory failure with inadequate or inappropriately distributed tissue perfusion resulting in generalized cellular hypoxia.

Hypovolaemic – loss of circulatory volume (eg. haemorrhage, burns)

Cardiogenic – failure of the heart to act as an effective pump (eg. ischaemic heart disease)

Obstructive – mechanical impediments to forward flow

Obstruction to outflow (eg. pulmonary embolus)

Restricted cardiac filling (eg. cardiac tamponade, tension pneumothorax)

Distributive – abnormalities of the peripheral circulation (eg. sepsis, anaphylaxis)

Stages of shock

1. Non-progressive phase

Baroreceptor reflex, adrenaline and noradrenaline release (increased TPR, HR, CO).

Renin-angiotensin activation, release of vasopressin from pituitary (increased blood volume).

Net effect is to increase blood pressure back to normal.

2. Progressive phase

Generalised tissue hypoxia leads to cells switching to anaerobic respiration and eventually lactic acidosis occurs. The lactic acid causes vasodilation and blood starts to pool in microcirculation and more blood fluids will leak into surrounding tissue.

3. Irreversible phase

Generalised tissue injury leads to irreversible organ failure. Death eventuates.

References: Kumar and Clark Clinical Medicine, Robbins Basic Pathology