(See also Low Blood Pressure 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 .)
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.
In the United States, hospital emergency departments report more than 1 million cases of shock each year. 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...
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...
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
Excessive loss of body fluids
Inadequate fluid intake (less common)
Blood may be rapidly lost because of
External bleeding, such as that caused by an injury
Internal bleeding, such as that caused by an ulcer in the stomach or intestine (gastrointestinal bleeding Gastrointestinal Bleeding Bleeding may occur anywhere along the digestive (gastrointestinal [GI]) tract, from the mouth to the anus. Blood may be easily seen by the naked eye (overt), or blood may be present in amounts... read more ), a ruptured blood vessel, or a ruptured ectopic pregnancy (a pregnancy outside the uterus)
An excessive loss of body fluids other than blood can result from
Perforation of the intestinal wall
Severe diarrhea Diarrhea in Adults Diarrhea is an increase in the volume, wateriness, or frequency of bowel movements. (See also Diarrhea in Children.) The frequency of bowel movements alone is not the defining feature of diarrhea... read more or vomiting Nausea and Vomiting in Adults Nausea is an unpleasant feeling of needing to vomit. People also may feel dizziness, vague discomfort in the abdomen, and an unwillingness to eat. Vomiting is a forceful contraction of the stomach... read more
Some kidney disorders
Excessive use of diuretics, which increase the output of urine
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.
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
Sudden malfunction of a heart valve (particularly an artificial valve Overview of Heart Valve Disorders Heart valves regulate the flow of blood through the heart's four chambers—two small, round upper chambers (atria) and two larger, cone-shaped lower chambers (ventricles). Each ventricle has... read more )
Infections of the heart muscle (myocarditis Myocarditis Myocarditis is inflammation of the muscle tissue of the heart (myocardium) that causes tissue death. Myocarditis may be caused by many disorders, including infection, toxins and drugs that affect... read more ) or the heart valves (endocarditis Infective Endocarditis Infective endocarditis is an infection of the lining of the heart (endocardium) and usually also of the heart valves. Infective endocarditis occurs when bacteria enter the bloodstream and travel... read more )
Inability of the heart to fill due to sudden buildup of fluid in the sac that surrounds the heart (cardiac tamponade Cardiac Tamponade Cardiac tamponade is pressure on the heart by blood or fluid that accumulates in the two-layered sac around the heart (pericardium). This disorder interferes with the heart's ability to... read more )
Other disorders affecting the structure of the heart, for example, rupture of the wall of the heart (myocardial rupture Myocardial rupture The heart muscle needs a constant supply of oxygen-rich blood. The coronary arteries, which branch off the aorta just after it leaves the heart, deliver this blood. An acute coronary syndrome... read more )
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
A severe bacterial infection (shock caused by such an infection is called septic shock Introduction to Bacteremia, Sepsis, and Septic Shock )
Overdose of drugs or poisons that dilate blood vessels
Injuries to the spinal cord and rarely the brain (neurogenic shock)
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 and pale.
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
Other tests depending on the probable cause
The diagnosis of shock is based mainly on evidence of organ damage 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.
Other tests are done depending on the probable cause of shock. For example, doctors do cultures of blood and other body fluids Culture of Microorganisms Infectious diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites. Doctors suspect an infection based on the person's symptoms, physical examination results,... read more if they suspect severe infection. They may do electrocardiography Electrocardiography Electrocardiography (ECG) is a quick, simple, painless procedure in which the heart’s electrical impulses are amplified and recorded. This record, the electrocardiogram (also known as an ECG)... read more and other cardiac imaging tests Diagnosis of Heart and Blood Vessel Disorders if the person has signs of heart problems.
Prognosis of Shock
If untreated, shock is usually fatal. If shock is treated, the outlook depends on the
Cause of the shock
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
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... read more 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.
When shock is caused by an inadequate pumping action of the heart, efforts are made to improve the heart’s performance. In addition to fluids and drugs, other treatments include percutaneous transluminal coronary angioplasty Percutaneous Coronary Intervention Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more (PTCA) or coronary artery bypass grafting Coronary Artery Bypass Grafting Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more if the cause is a heart attack. Surgery may also be needed if the cause is a damaged heart valve Overview of Heart Valve Disorders Heart valves regulate the flow of blood through the heart's four chambers—two small, round upper chambers (atria) and two larger, cone-shaped lower chambers (ventricles). Each ventricle has... read more or rupture of a wall of the heart. Excess fluid that compresses the heart, a condition called cardiac tamponade Cardiac Tamponade Cardiac tamponade is pressure on the heart by blood or fluid that accumulates in the two-layered sac around the heart (pericardium). This disorder interferes with the heart's ability to... read more , can be removed with a needle or surgery.
When shock is caused by an infection (such as sepsis 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 ), treatment of the infection includes antibiotics and removal of the source of infection. When shock is caused by bleeding, surgery may be necessary to stop the bleeding. If shock is caused by an endocrine disorder (such as Addison disease Adrenal Insufficiency In adrenal insufficiency, the adrenal glands do not produce enough adrenal hormones. Adrenal insufficiency may be caused by a disorder of the adrenal glands, a disorder of the pituitary gland... read more ) or anaphylaxis Anaphylactic Reactions Anaphylactic reactions are sudden, widespread, potentially severe and life-threatening allergic reactions. Anaphylactic reactions often begin with a feeling of uneasiness, followed by tingling... read more , a corticosteroid drug may need to be given.