Low blood pressure, or hypotension, occurs when blood pressure during and after each heart beat is much lower than usual. This means the heart, brain, and other parts of the body do not get enough blood. Dizziness or lightheadedness can result.

See also: Blood pressure

Blood pressure that is borderline low for one person may be normal for another. The most important factor is how the blood pressure changes from the normal condition.

Most normal blood pressures fall in the range of 90/60 millimeters of mercury (mm Hg) to 130/80 mm Hg. But a significant drop, even as little as 20 mm Hg, can cause problems for some people.

There are three main types of hypotension:

• Orthostatic hypotension, including postprandial orthostatic hypotension
• Neurally mediated hypotension (NMH)
• Severe hypotension brought on by a sudden loss of blood (shock)

Orthostatic hypotension is brought on by a sudden change in body position, usually when shifting from lying down to standing. This type of hypotension usually lasts only a few seconds or minutes. If this type of hypotension occurs after eating, it is called postprandial orthostatic hypotension. This form most commonly affects older adults, those with high blood pressure, and persons with Parkinson's disease.

NMH most often affects young adults and children. It occurs when a person has been standing for a long time. You might feel dizzy, faint, or have an upset stomach. Children usually outgrow this type of hypotension.

Severe hypotension starves your body of oxygen, which can cause damage to the heart, brain, and other organs. This type of hypotension can be life threatening if not immediately treated.

Low blood pressure is commonly caused by drugs such as:

• Medications used for surgery
• Anti-anxiety medications
• Heart medicines, including those used to treat high blood pressure and coronary heart disease
• Diuretics
• Certain antidepressants
• Pain killers
• Alcohol

Other causes of low blood pressure include:

• Dehydration
• Heart failure
• Heart attack
• Changes in heart rhythm (arrhythmias)
• Fainting
• Anaphylaxis (a life-threatening allergic response)
• Shock (from severe infection, stroke, anaphylaxis, major trauma, or heart attack)
• Advanced diabetes

Symptoms may include:

• Blurry vision
• Confusion
• Dizziness
• Fainting (syncope)
• Lightheadedness
• Sleepiness
• Weakness

A sudden drop in blood pressure that causes a sudden, brief loss of consciousness (syncope) can lead to accidents, including falls. Falls are particularly dangerous for older adults. Fall-related injuries, such as a broken hip, can dramatically impact a person's quality of life.

The health care provider will examine you and try to determine what is causing the low blood pressure. Your vital signs (temperature, pulse, rate of breathing, blood pressure) will be checked frequently. You may need to stay in the hospital for a while.

The doctor will ask questions, including:

• What is your normal blood pressure?
• What medications do you take?
• Have you been eating and drinking normally?
• Have you have any recent illness, accident, or injury?
• What other symptoms do you have?
• Did you faint or become less alert?
• Do you feel dizzy or light-headed when standing or sitting after lying down?

The following tests may be done:

• Complete blood count ( CBC) and other blood tests, including blood differential
• Blood cultures to check for infection
• ECG
• Urinalysis
• X-ray of the abdomen
• X-ray of the chest

Hypotension in a healthy person that does not cause any problems usually doesn't require treatment.

If you have signs or symptoms of low blood pressure, you may need treatment. Treatment depends on the cause of your low blood pressure. Severe hypotension caused by shock is a medical emergency. You may be given blood through a needle (IV), medicines to increase blood pressure and improve heart strength, and other medicines, such as antibiotics. For more details, see the article on shock.

If you have orthostatic hypotension caused by medicines, your doctor may change the dose or switch you to a different drug. DO NOT stop taking any medicine before talking to your doctor. Other treatments for orthostatic hypotension include increasing fluids to treat dehydration or wearing elastic hose to boost blood pressure in the lower part of the body.

Those with NMH should avoid triggers, such as standing for a long period of time. Other treatments involve drinking plenty of fluids and increasing the amount of salt in your diet. (Ask your doctor about specific recommendations.) In severe cases, medicines such as fludrocortisone may be prescribed.

Low blood pressure can usually be treated with success.

• Injury from falls due to fainting
• Shock

When you have symptoms from a drop in blood pressure, you should immediately sit or lie down and raise your feet above heart level.

If low blood pressure causes a person to pass out (become unconscious), seek immediate medical treatment or call the local emergency number (such as 911). If the person is not breathing or has no pulse, begin CPR.

Call your doctor immediately if any of the following symptoms occur:

• Dizziness, lightheadedness
• Fainting
• Black or maroon stools
• Chest pain
• Shortness of breath
• Irregular heartbeat
• Fever higher than 101 degrees

Also call your doctor if you have:

• Cough with phlegm
• Prolonged diarrhea or vomiting
• Inability to eat or drink
• Burning with urination or other urinary symptoms

If you have low blood pressure, your doctor may recommend certain steps to prevent or reduce your symptoms. This may include:

• Drinking plenty of fluids
• Avoiding alcohol
• Getting up slowly after sitting or lying down
• Using compression stockings to increase blood pressure in the legs
• Avoiding standing for a long time (if you have NMH)