What is shock?

Shock is a caricature of the physiological response to haemorrhage; as it progresses, the defensive attributes are replaced by adverse effects on circulation, reticuloendothelial function, respiration and metabolism. Haemorrhage is only one possible cause of shock and any severe reduction of circulating fluid volume can potentially trigger similar responses. Indeed despite the existence of several types of shock (e.g. anaphylactic, endotoxin, septic) the ‘final common path’ is remarkably similar and consists of a widespread failure of capillary perfusion. The essential prerequisite for effective perfusion is not merely the presence of blood in capillaries but its efficient movement through them. Thus viscosity is a key property of blood in shock and a limited fall in PCV may improve oxygen delivery. The pathophysiology of shock is discussed in relation to its therapeutic implications, notably the relative importance of fluid therapy, antibiotics and corticosteroids, the limitations on the effectiveness of antihistamines and α-blockers, and more recent work with Mg-ATP, hypertonic solutions, prostaglandins, endogenous opiates and dopamine.