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Definition

Shock occurs when the body's organs and tissues do not receive an adequate flow of blood. Inadequate blood flow deprives the organs and tissues of oxygen and allows the buildup of waste products. Shock is a medical emergency and can result in serious damage or even death.

Description

There are three stages of shock: Stage I (also called compensated, or nonprogressive), Stage II (also called decompensated or progressive), and Stage III (also called irreversible).

In Stage I of shock, when low blood flow (perfusion) is first detected, a number of systems are activated in order to maintain or restore perfusion. The result is that the heart beats faster, the blood vessels throughout the body become slightly smaller in diameter, and the kidney works to retain fluid in the circulatory system. All this serves to maximize blood flow to the most important organs and systems in the body. A person in this stage of shock has very few symptoms, and treatment can completely halt any progression.

In Stage II of shock, the body's standard methods of compensation begin to fail and are unable to improve perfusion any longer. Oxygen deprivation in the brain causes the person to become confused and disoriented, while oxygen deprivation in the heart may cause chest pain. With quick and appropriate treatment, this stage of shock can be reversed.

In Stage III of shock, the length of time that poor perfusion has existed begins to take a permanent toll on the body's organs and tissues. The heart's functioning continues to spiral downward, and the kidneys usually shut down completely. Cells in organs and tissues throughout the body are injured and dying. The endpoint of Stage III shock is death.

Causes and symptoms

Shock is caused by three major categories of problems: cardiogenic (problems associated with the heart's functioning); hypovolemic (total volume of blood available to circulate is low); and septic shock (overwhelming infection, usually by bacteria).

Cardiogenic shock can be caused by any disease or event which prevents the heart muscle from pumping strongly and consistently enough to circulate the blood in a normal fashion. Heart attack, conditions which cause inflammation of the heart muscle (myocarditis), disturbances of the electrical rhythm of the heart, and any kind of mass or fluid accumulation or blood clot which interferes with flow out of the heart can significantly affect the heart's ability to pump a normal quantity of blood.

Hypovolemic shock occurs when the total volume of blood in the body falls well below normal. This can occur when there is excess fluid loss, as in dehydration due to severe vomiting or diarrhea, diseases which cause excess urination (diabetes insipidus, diabetes mellitus, and kidney failure), extensive burns, blockage in the intestine, inflammation of the pancreas (pancreatitis), or severe bleeding of any kind.

Septic shock can occur when an untreated or inadequately treated infection (usually bacterial) is allowed to progress. Bacteria often produce poisonous chemicals (toxins) which can cause injury throughout the body. When large quantities of these bacteria and their toxins begin circulating in the bloodstream, every organ and tissue is at risk of their damaging effects. The most damaging consequences include poor functioning of the heart muscle; widening of the diameter of the blood vessels; a drop in blood pressure; activation of the blood clotting system, causing blood clots, followed by a risk of uncontrollable bleeding; damage to the lungs, causing acute respiratory distress syndrome; liver failure; kidney failure; and coma.

Initial symptoms of shock include cold, clammy hands and feet; pale or blue-tinged skin tone; weak, fast pulse rate; fast rate of breathing; low blood pressure. A variety of other symptoms may be present, but they are dependent on the underlying cause of shock.

Diagnosis

Diagnosis of shock is based on a person's symptoms, as well as criteria including a significant drop in blood pressure, extremely low urine output, and blood tests that reveal overly acidic blood with a low circulating concentration of carbon dioxide. Other tests are performed, as appropriate, to try to determine the underlying condition responsible for an individual's state of shock.

Treatment

The most important goals in treating shock include quickly diagnosing a person's state of shock; quickly intervening to halt the underlying condition (stopping bleeding, re-starting the heart, giving antibiotics to combat an infection, etc.); treating the effects of shock (low oxygen, increased acid in the blood, activation of the blood clotting system); and supporting vital functions (blood pressure, urine flow, heart function).

Treatment includes keeping a person warm, with legs raised and head down to improve blood flow to the brain, putting a needle in a vein in order to give fluids or blood transfusions, as necessary; giving a person extra oxygen to breathe and medications to improve the heart's functioning; and treating the underlying condition which led to shock.

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KEY TERMS

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Cardiogenic—Originating with the heart.

Deprivation—A condition of having too little of something.

Hypovolemic—Having a low volume.

Perfusion—Blood flow through an organ or tissue.

Sepsis—An overwhelming infection throughout the body, usually caused by bacteria in the bloodstream.

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Prognosis

The prognosis of an individual in shock depends on the stage of shock when treatment was begun, the under-lying condition causing shock, and the general medical state of the person.

Health care team roles

First aid is often given by appropriately trained individuals. Physicians supervise the treatment of shock in a hospital setting. Nurses provide bedside management and patient-family education.

Prevention

The most preventable type of shock is caused by dehydration during illnesses with severe vomiting or diarrhea. Shock can be avoided by recognizing that a person who is unable to drink in order to replace lost fluids needs to be given fluids intravenously (through a needle in a vein). Other types of shock are only preventable insofar as one can prevent their underlying conditions or can monitor and manage those conditions well enough so that they never progress to the point of shock.

L. Fleming Fallon, Jr., MD, DrPH