In lay usage this refers to fright, horror or any acute distress. Medically it is quite different and refers to a state of acute circulatory failure in which the heart's output of blood is inadequate to provide normal PERFUSION of the major organs. It is accompanied by a fall in arterial blood pressure and is characterised by systemic arterial hypotension (arterial blood pressure less than 80), sweating and signs of VASOCONSTRICTION (for example, pallor, CYANOSIS, a cold clammy skin and a low-volume pulse). These signs may be associated with clinical evidence of poor blood supply to body tissues (poor perfusion), for example to the brain and kidneys, leading to mental apathy, confusion or restlessness and OLIGURIA.
Shock may result from loss of blood or plasma volume. This may occur from haemorrhage or severe diarrhoea and vomiting. It may also result from blood leaving the vessels due to such causes as ANAPHYLAXIS or SEPTICAEMIA in which leakage through capillaries reduces circulating blood volume. Cardiogenic shock is due to failure of the heart as a pump and most commonly seen as a result of myocardial infarction (see under HEART, DISEASES OF).
If failure of adequate blood flow to vital organs is prolonged, the effects can be disastrous. The ischaemic intestine permits the transfer of toxic bacterial products and proteins across its wall into the blood; renal ISCHAEMIA prevents the maintenance of a normal electrolyte and acid-base balance.
Haemorrhage, diarrhoea or vomiting are treated by replacement of blood, lost fluid and ELECTROLYTES. If shock is due to septicaemia, high dose antibiotics, high-volume intravenous fluids and vasopressor drugs are used. Cardiogenic shock is treated by attention to the underlying cause. Full intensive care is likely to be required, and artificial ventilation and DIALYSIS may both be needed.