Section 3. Heart and Blood Vessel Disorders

Chapter 24. Shock

Topic: Shock

Shock

Shock is a life-threatening condition in which blood pressure is too low to sustain life.

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 very low--much lower and for a longer time than the low blood pressure that causes fainting (syncope (see Section 3, Chapter 23)). When blood pressure is very low, the body's cells do not receive enough blood and therefore do not receive enough oxygen. As a result, cells can be quickly and irreversibly damaged and die; organs, including the brain, kidneys, liver, and heart, may cease to function normally. People in shock require immediate emergency treatment.

Shock has several causes: a low blood volume, which causes hypovolemic shock; inadequate pumping action of the heart, which causes cardiogenic shock; or excessive widening of blood vessels, which causes vasodilatory shock. These types of shock are unrelated to another condition called shock that is caused by emotional stress.

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. Blood volume may be low because of severe bleeding, an excessive loss of body fluids, or inadequate fluid intake. Blood may be rapidly lost because of external bleeding, such as that caused by an accident, or internal bleeding, such as that caused by an ulcer in the stomach or intestine, 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 major burns, inflammation of the pancreas (pancreatitis), perforation of the intestinal wall, severe diarrhea, kidney disease, or excessive use of loop diuretics, which increase the output of urine (see Section 3, Chapter 22). Fluid intake may be inadequate because a physical disability (such as severe joint disease) or a mental disability (such as Alzheimer's disease) prevents people from obtaining enough fluids even though they 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 inadequate pumping action may result from a heart attack, pulmonary embolism, malfunction of a heart valve (particularly an artificial valve), rupture of the wall between the two sides of the heart (septum (see Section 3, Chapter 33)), or an abnormal heart rhythm (arrhythmia).

Excessive dilation of blood vessels (vasodilation) increases the capacity of blood vessels, so that blood meets with less resistance as it flows through them. Blood vessels may be excessively dilated because of a head injury, liver failure, poisoning, overdoses of drugs that dilate blood vessels, or a severe bacterial infection (shock caused by such an infection is called septic shock (see Section 17, Chapter 191)). The mechanisms by which these conditions cause vasodilation vary. For example, a head injury may affect the area in the brain that maintains the tone of arteries; poisons or toxins released by bacteria can cause the blood vessels to dilate.

Symptoms and Diagnosis

Symptoms of shock are similar when the cause is low blood volume or inadequate pumping action of the heart. The condition may begin with lethargy, 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. A bluish network of lines may appear under the skin. The pulse is weak and rapid, unless a slow heartbeat is causing the shock. Usually, 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. Eventually, the person cannot sit up without passing out and may die.

When shock results from excessive dilation of blood vessels, the symptoms are somewhat different. The skin may be warm and flushed, 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, many symptoms may be absent or may be undetected unless they are specifically looked for. In older people, the only symptom may be confusion. The blood pressure is very low. Urine flow is very reduced (because blood supply to the kidneys is reduced), and waste products build up in the blood.

Prognosis and Treatment

If untreated, shock is usually fatal. If shock is treated, the outlook depends on the cause, the other disorders the person has, the amount of time that passes before treatment begins, and the type of treatment given. 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 great.

The first person to arrive on the scene can take several measures that help, including calling for additional help. A person who is in shock should be laid down and kept warm, with the legs elevated about 12 to 24 inches to facilitate the return of blood to the heart. Any bleeding should be stopped, and breathing should be checked. The head should be turned to the side to prevent inhalation of vomit. Nothing should be given by mouth.

When emergency medical personnel arrive, they may provide oxygen given through a face mask or a mechanical device to assist breathing. Drugs, if needed, are given intravenously. Opioids (narcotics) and sedatives are usually not used because they tend to decrease blood pressure. Attempts may be made to increase blood pressure with military (or medical) antishock trousers (MAST). These pants apply pressure to the lower body, thus driving blood from the legs to the heart and brain. Fluids are given intravenously at a fast rate and in large volumes. Usually, blood is cross-matched before a blood transfusion is given, but in an emergency when there is no time for crossmatching, type O negative blood can be given to anyone.

The intravenous fluid and blood transfusion may not be enough to counteract the shock if bleeding or fluid loss continues or if the shock is caused by a heart attack or another problem unrelated to blood volume. Drugs that constrict the blood vessels may be given to boost blood flow to the brain or heart. However, such drugs should be used as briefly as possible because they can reduce blood flow to other tissues in the body.

When shock is caused by an inadequate pumping action of the heart, efforts are made to improve the heart's performance. The rate and rhythm abnormalities of the heartbeat are corrected, and blood volume is increased if necessary. Atropine may be used to increase a slow heart rate, and other drugs may be given to improve the ability of the heart muscle to contract.

If the cause is a heart attack and shock persists after emergency treatment, a balloon pump may be inserted into the aorta to reverse shock temporarily. After this procedure, emergency percutaneous transluminal coronary angioplasty (PTCA) or coronary artery bypass surgery (see Section 3, Chapter 33) may be needed. By opening a blocked coronary artery (one of the arteries supplying the heart muscle), emergency PTCA can improve the heart's pumping action and can reverse the shock. If emergency PTCA or bypass surgery is not performed, a drug that helps break up clots (thrombolytic drug) is given as soon as possible, unless it could worsen problems in people who have another disorder, such as a bleeding ulcer, or who have had a stroke recently.

If the cause is a malfunctioning heart valve or rupture of the septum, surgery may also be needed.

Shock caused by excessive dilation of the blood vessels is treated primarily with drugs that constrict the vessels. The cause of the excessive dilation is also treated. For example, a bacterial infection is treated with antibiotics.