Merck Manual

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Levi D. Procter

, MD, Virginia Commonwealth University School of Medicine

Reviewed/Revised Jun 2022 | Modified Sep 2022
Topic Resources

Shock is a life-threatening condition in which blood flow to the organs is low, decreasing delivery of oxygen and thus causing organ damage and sometimes death. Blood pressure is usually low.

  • Shock has several causes: Low blood volume, inadequate pumping action of the heart, or excessive widening (dilation) of blood vessels.

  • When shock is caused by low blood volume or inadequate pumping of the heart, people may feel sluggish, sleepy, or confused, and their skin becomes cold and sweaty and often bluish and pale.

  • When shock results from excessive dilation of blood vessels, the skin may be warm and flushed, and the pulse may be strong and forceful (bounding) rather than weak.

  • People who are in shock should be kept warm and positioned so their legs are elevated.

  • Intravenous fluids, oxygen, and sometimes drugs are given to help restore the blood pressure.

Many people who are in shock are brought to emergency departments every day. People go into shock when their blood pressure becomes so low Low Blood Pressure Low blood pressure is blood pressure low enough to cause symptoms such as dizziness and fainting. Very low blood pressure can cause damage to organs, a process called shock. Various drugs and... read more that the body’s cells do not receive enough blood and therefore do not receive enough oxygen. As a result, cells in numerous organs, including the brain, kidneys, liver, and heart, stop functioning normally. If blood flow (perfusion) to these cells is not quickly restored, they become irreversibly damaged and die. If enough cells are damaged or dead, the organ they are in may fail and the person may die.

Multiple organ dysfunction syndrome (MODS) is the failure of two or more organs. This diagnosis carries a significant chance of death. People in shock require immediate emergency treatment and are usually cared for in the hospital intensive care unit.

Did You Know...

  • Shock has nothing to do with sudden emotional stress.

Although low blood pressure is generally the cause of shock, blood pressure may not be low in the early stages of shock. Also, blood pressure can be low in people who do not have shock.

The medical disorder of shock has nothing to do with the “shock” that people feel from a sudden emotional stress.

Causes of Shock

Shock has several causes:

Did You Know...

  • In some people with shock, blood pressure is so low that it cannot be measured with a blood pressure cuff.

Hypovolemic shock

Low blood volume results in less-than-normal amounts of blood entering the heart with every heartbeat and therefore less-than-normal amounts of blood being pumped out to the body and its cells.

Blood volume may be low because of

  • Severe bleeding

  • Excessive loss of body fluids

  • Inadequate fluid intake (less common)

Blood may be rapidly lost because of

An excessive loss of body fluids other than blood can result from

Fluid intake may be inadequate because a physical disability (such as severe joint disease) or a mental disability (such as Alzheimer disease) may prevent people from obtaining enough fluids even though they may feel thirsty.

Cardiogenic shock

Inadequate pumping action of the heart can also result in less-than-normal amounts of blood being pumped out with every heartbeat. The most common causes of inadequate pumping action are

Distributive shock

Excessive dilation of blood vessels (vasodilation) increases the capacity of blood vessels and decreases blood pressure. This can decrease blood flow and oxygen delivery to organs.

Blood vessels may be excessively dilated because of

The mechanisms by which these conditions cause vasodilation vary. For example, a spinal cord injury interrupts the nerves from the brain to the blood vessels that normally cause blood vessel constriction; poisons or toxins released by bacteria can directly cause the blood vessels to dilate.

Symptoms of Shock

Symptoms of shock are similar when the cause is low blood volume or inadequate pumping action of the heart.

  • The condition may begin with sluggishness, sleepiness, and confusion.

  • The skin becomes cold and sweaty and often bluish, pale or ashen.

  • If the skin is pressed, color returns much more slowly than normal.

  • Blood vessels may become more visible as a bluish network of lines under the skin.

  • The pulse is weak and rapid, unless a slow heartbeat is causing the shock.

  • Usually, the person cannot sit up without feeling light-headed or passing out.

  • Breathing is rapid, but breathing and the pulse may both slow down if death is imminent.

  • Blood pressure drops so low that it often cannot be measured with a blood pressure cuff.

  • Urination decreases and eventually stops

  • Eventually, the person may go into a coma and die.

When shock results from excessive dilation of blood vessels, the symptoms are somewhat different. The skin may be warm and flushed, and the pulse may be strong and forceful (bounding) rather than weak, particularly at first. However, later on, shock due to excessive dilation of blood vessels also produces cold, clammy skin and lethargy.

In the earliest stages of shock, especially septic shock Sepsis and Septic Shock Sepsis is a serious bodywide response to bacteremia or another infection plus malfunction or failure of an essential system in the body. Septic shock is life-threatening low blood pressure ... read more , many symptoms may be absent or may be undetected unless they are specifically looked for. In older people, the only symptom may be confusion. Urine flow may be reduced (because blood supply to the kidneys is reduced), and waste products may build up in the blood. The blood pressure may be low.

Diagnosis of Shock

  • Doctor's evaluation

  • Blood tests

  • Other tests depending on the probable cause

The diagnosis of shock is based mainly on evidence of organ malfunction found on a doctor's evaluation. For example, people

  • May have a reduced level of consciousness

  • May not be producing urine

  • May have bluish fingers or toes

People may also show signs of trying to compensate for their low blood volume or their heart's inadequate pumping. For example, they may have a rapid heart rate, be breathing rapidly, or be perspiring profusely.

Blood tests can help the diagnosis, but no finding alone is diagnostic, and doctors evaluate each by its trend (ie, worsening or improving) and in light of the person's overall condition.

One blood test (the level of lactate) measures the amount of waste products of cellular activity in the blood. An elevated blood lactate level suggests to the doctor that the organs are not receiving enough oxygen and blood and that the person may have shock.

Blood tests that show a high or low white blood cell count Complete blood count Doctors select tests to help diagnose blood disorders based on the person's symptoms and the results of the physical examination. Sometimes a blood disorder causes no symptoms but is discovered... read more or bacteria or other microorganisms in the blood may help determine that the person has an infection that could be causing septic shock.

Blood tests may also indicate damage to specific organs. For example, a high level of creatinine can indicate that the kidneys are damaged, and a high level of troponin (a cardiac biomarker) can indicate that the heart is damaged.

Prognosis for Shock

Untreated shock is usually fatal. If shock is treated, the outlook depends on the

  • Cause of the shock

  • Person's age

  • Other disorders the person has

  • Presence and severity of any organ failure

  • Amount of time that passes before treatment begins

  • Type of treatment given

Multiple organ dysfunction syndrome carries a significant risk of death. The risk of death increases as the number of affected organs increases. Regardless of treatment, the likelihood of death due to shock after a massive heart attack or due to septic shock, especially in older people, is high.

Treatment of Shock

  • Calling for help and stopping any bleeding

  • Intravenous (IV) fluids and/or blood transfusions

  • Sometimes drugs to help increase blood pressure

  • Other measures depending on cause

Initial treatment

Most important is to call for help and stop any major bleeding. After doing that, the person can be laid down and kept warm, with the legs elevated.

When emergency medical personnel arrive, they may provide oxygen through a face mask or insert a breathing tube. Fluids may be given by vein (intravenously) at a fast rate and in large volumes to raise blood pressure.

On arrival at an emergency department, the person may be given a blood transfusion Overview of Blood Transfusion A blood transfusion is the transfer of blood or a blood component from one healthy person (a donor) to a sick person (a recipient). Transfusions are given to increase the blood's ability to... read more Overview of Blood Transfusion if shock is caused by bleeding. Usually, blood is cross-matched before transfusion, but in an emergency when there is no time for crossmatching, type O negative blood can be given to anyone.

If shock is caused by severe infection, doctors give intravenous fluids and antibiotics. If shock is caused by a heart attack or other heart problem, other procedures or surgery may be needed.

For some types of shock, drugs may be given intravenously to increase blood pressure. However, doctors use such drugs for as brief a time as possible because they can reduce blood flow to other tissues in the body or cause heart rhythm problems. Drugs can increase blood pressure by

  • Constricting blood vessels, which happens, for example, when doctors give epinephrine (used for people with anaphylaxis) or norepinephrine (sometimes used for people with other forms of shock)

  • Increasing the ability of heart to pump blood, which happens, for example, when doctors give dobutamine or milrinone

Treatment of cause

Fluids given intravenously, blood transfusions, and drugs may not be enough to counteract shock if bleeding or fluid loss continues or if shock is caused by a heart attack, infection, or another problem unrelated to blood volume. Treating the cause of shock is vital.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Adrenaclick, Adrenalin, Auvi-Q, Epifrin, EpiPen, Epipen Jr , Primatene Mist, SYMJEPI, Twinject
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