Shock

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This article is about medicine. For the concept of shock in physics and mechanics, see Shock (mechanics).

In medicine, shock is a life-threatening medical emergency characterized by inability of the body to supply enough oxygen to meet tissue requirements. Most causes of shock result in a reduced cardiac output. Shock may rapidly progress to death without medical intervention.

Table of contents

Types of shock

The commonest causes of shock is blood loss or severe burns leading to hypovolemic shock. It is necessary to immediately control bleeding and restore the victims blood volume by giving intravenous fluids and, possibly, blood transfusions.

Cardiogenic shock is 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. Other causes of cardiogenic shock include cardiac tamponade, arrhythmias, or cardiac valve problems.

Septic shock is caused by overwhelming infection leading to vasodilation. Despite a generally increased cardiac output the body is unable to meet the demand for oxygen. It is treated by antibiotics, fluid replacement, and vasoconstrictors.

Less commonly severe anaphylactic reactions may cause anaphylactic shock as allergens trigger widespread vasodilation and movement of fluid out of the blood into the tissues.

The rarest cause of shock is acute spinal cord injury leading to neurogenic shock. Neurogenic shock is caused by the sudden loss of the sympathetic nervous system signals to the smooth muscle in vessel walls. Without this constant stimulation the vessels relax resulting in a sudden decrease in peripheral vascular resistance and decreased blood pressure.

Symptoms and signs

The external signs and symptoms of shock are:

feeling of thickness, weakness, thirst;
pallor, especially visible at the inner side of the lips when the casualty has a dark skin;
rapid pulse (tachycardia, more than 120 per second), the radial pulse is difficult to feel;
when pressing a finger nail, it takes more than two seconds for the colour to come back;
confusion or anxiety;

Other signs can be evaluated:

Patients with hypovolaemic or cardiogenic shock will have cold and clammy hands and feet. Septic, anaphylactic and neurogenic shock may present with warm extremities.

In fact, the shock is a drop of blood pressure (below 80 mmHg), and the symptoms are a reaction to this state:

as the pressure is low, the pulse is hard to feel and the nails colour back slowly;
the transport of oxygen by the blood is less efficient, so the blood is concentrated in the important organs through peripheral vasoconstriction (causing pallor), and the heart beat and breath is accelerated to increase the oxygen transport rate;
the thirst and decreased urine production expresses the loss of body liquid; but giving to drink is more detrimental than beneficial:
- one of the probable evolution is the loss of alertness; in such a case, the casualty loses its protection reflexes and the content of the stomach can go to the lungs (the acidic product causes the Mendelson syndrom, therefore the recovery position to avoid this deadly situation); this lung invasion is more likely to happen when the stomach is full, especially with liquid;
- the casualty will need surgery and thus anaesthesia; a full stomach is not recommended for an anaesthesia.

The loss of liquid is medically compensated by intravenous drip and not per os (through the mouth).

Treatment

Shock is a medical emergency. First aid treatment includes calling for help, controlling any external bleeding and giving oxygen if it is available. CPR may be necessary if the casualty stops breathing.

Although this is a protection reaction, the shock itself will induce problems; the circulatory system being less efficent, the body gets "exhausted" and finally, the blood circulation and the breathing slow down and finally stop (cardiac arrest). The main way to avoid this deadly consequence is to make the blood pressure rise agin with

vessel filling with intravenous drip;
use of vasopressing drugs (e.g. to induce vasoconstriction);
use of antishock pants that compress the legs and concentrate the blood in the important organs (lungs, heart, brain).
use of blanket/s to keep the patient warm - Mylar emergency blankets are used to reflect the patient's body heat back to the patient.

Some patients, especially those with reduced levels of consciousness, require immediate intubation and mechanical ventilation.

These aim of these acts is only to allow the survival during the transportation to the hospital; they do not cure the cause of the shock. Specific treatment depends on the cause.

A compromise must be searched between:

rising the blood pressure to be able to transport "safely" (when the blood pressure is too low, any motion can lower the heart and brain perfusion and cause death);
respecting the Golden Hour: when surgery is needed, it must be performed within the first hour.

The is the play and run versus the scoop and run debate.

Prognosis

The prognosis of shock depends on the underlying cause and the nature and extent of concurrent problems.

Hypovolaemic, anaphylactic and neurogenic shock are readily treatable and respond well to medical therapy. Septic shock however, is a grave condition and with a mortality rate between 30% and 50%. The prognosis of cardiogenic shock is even worse.

Shock is said to evolve from reversible to irreversible. This clinical distinction is generally only made retrospectivly. Most cases of untreated reversible shock progress to irreversible shock within six hours due to hypoxic tissue damage.

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