In medicine, shock is a life-threatening medical emergency characterized by profoundly low blood pressure and tissue hypoperfusion. It may progress to death unless there is immediate medical intervention.

Definition

Shock is decrease SBP < 90 or at least 40 less than baseline BP + signs of hypoperfusion or organ dysfunction.

Consider as serious: a systolic BP < 90 or a decrease of >40 than normal readings in a previously hypertensive patient. Another common but not essential manifestation is metabolic acidosis.

Some common causes of shock are:

hypovolemic shock is caused by loss of blood volume. It is necessary to immediately control any bleeding. Intravenous fluids and blood transfusions may be needed to save the person's life.
septic shock is caused by overwhelming infection and is treated by massive doses of antibiotics, fluid replacement, and vasoactive drugs. Septic shock is often fatal if untreated.
cardiogenic shock is hypotension caused by the failure of the heart to pump effectively. This can be due to damage to the heart muscle, most often from a large myocardial infarction, to mechanical impairment of the heart's ability to pump blood (cardiac tamponade), cardiac arrhythmia, or failure of a artificial pacemaker.
anaphylaxis is also sometimes called anaphylactic shock and is caused by allergens which trigger tissue swelling that can block the airway and cause suffocation.

Symptoms and signs

The signs and symptoms of shock include pallor, hypotension, tachycardia, cold and clammy extremities and altered mental state.

Sometimes, in cases of septic or toxic shock, the patient's hands and feet may initially be warm rather than cold and become clammy as the toxins cause peripheral vasodilatation.

Treatment

The proper treatment of shock is vital in the performance of first aid and comprises an essential part of the duties of the emergency medical technician, nurse, paramedic and doctor.

Quick diagnosis is of key importance. Resuscitation should be started immediately, the modality of which depends on the patient's requirements. Virtually all patients with shock will require some kind of intravenous access; obtaining venous access quickly is of paramount importance. Most people in shock require intravenous fluids. However, under certain circumstances such as in cardiogenic shock, too much fluid can be fatal, so a knowledgeable professional rather than a lay person should make these decisions.

Prognosis

Shock is sometimes classified into two stages - reversible shock and irreversible shock. The distinction between reversible and irreversible shock is clinical (and sometimes retrospective) - reversible shock is potentially treatable whereas irreversible shock inevitably leads to death. Most cases of untreated reversible shock will progress to irreversible shock within about six hours of onset.