What Causes Hypotension?

Factors or conditions that disrupt the body’s ability to control blood pressure cause hypotension. The different types of hypotension have different causes.

Orthostatic Hypotension

Orthostatic hypotension has many causes. Sometimes two or more factors combine to cause this type of low blood pressure.

Dehydration (de-hi-DRA-shun) is the most common cause of orthostatic hypotension. Dehydration occurs when the body loses more water than it takes in. You may become dehydrated if you don’t drink enough fluids or if you sweat a lot during physical activity. Fever, vomiting, and severe diarrhea also can lead to dehydration.

Orthostatic hypotension may occur during pregnancy, but it generally goes away after the birth.

Because an older body doesn’t manage changes in blood pressure as well as a younger body, getting older also can lead to this type of hypotension.

Postprandial hypotension (a type of orthostatic hypotension) mostly affects older adults. Postprandial hypotension is a sudden drop in blood pressure after a meal.

Certain medical conditions can raise your risk for orthostatic hypotension, including:

• Heart conditions, such as heart attack, heart valve disease, bradycardia (a very low heart rate), and heart failure. These conditions prevent the heart from pumping enough blood to the body.
• Anemia (uh-NEE-me-eh).
• Severe infections.
• Endocrine conditions, such as thyroid disorders, Addison’s disease, low blood sugar, and diabetes.
• Disorders of the central nervous system, such as Parkinson’s disease.
• Pulmonary embolism.

Some medicines used to treat high blood pressure and heart disease can raise your risk for orthostatic hypotension. These medicines include:

• Diuretics, or “water pills”
• Calcium channel blockers
• Angiotensin-converting enzyme (ACE) inhibitors
• Angiotensin II receptor blockers
• Nitrates
• Beta blockers

Medicines used to treat conditions such as anxiety, depression, erectile dysfunction, and central nervous system disorders (like Parkinson’s disease) also can increase your risk for orthostatic hypotension.

Other substances, when taken with high blood pressure medicines, also can lead to orthostatic hypotension. These substances include alcohol, barbiturates, and some prescription and over-the-counter medicines.

Finally, other factors or conditions that can trigger orthostatic hypotension include being out in the heat or being immobile (not being able to move around very much) for a long time.

Neurally Mediated Hypotension

Neurally mediated hypotension (NMH) occurs when the brain and heart don’t communicate with each other properly.

For example, when you stand for a long time, blood begins to pool in your legs. This causes your blood pressure to drop. In NHM, the body mistakenly tells the brain that blood pressure is high. In response, the brain slows the heart rate. This makes blood pressure drop even more, causing dizziness and other symptoms.

Severe Hypotension Linked to Shock

Many factors and conditions can cause severe hypotension linked to shock. Some of these factors also can cause orthostatic hypotension. In shock, though, blood pressure drops very low and doesn’t return to normal on its own.

Shock is an emergency and must be treated right away. If a person has signs or symptoms of shock, someone should call 9–1–1 right away.

Certain severe infections can cause shock. This is known as septic shock. It can occur when bacteria enter the bloodstream. The bacteria release a toxin (a poison) that leads to a dangerous drop in blood pressure.

A severe loss of blood or fluids from the body also can cause shock. This is known as hypovolemic (HI-po-vo-LE-mik) shock. Hypovolemic shock can happen as a result of:

• Major external bleeding (for example, from a severe cut or injury)
• Major internal bleeding (for example, from a ruptured blood vessel or injury that causes bleeding inside the body)
• Major loss of body fluids from severe burns
• Severe swelling of the pancreas (an organ that produces enzymes and hormones, such as insulin)
• Severe diarrhea
• Severe kidney disease
• Overuse of diuretics

A major decrease in the heart's ability to pump blood also can cause shock. This is known as cardiogenic (KAR-de-o-JEN-ik) shock. Heart attack, pulmonary embolism, or arrhythmia (an irregular heartbeat) can cause this type of shock.

A sudden and extreme widening of the arteries and drop in blood pressure also can cause shock. This is known as vasodilatory (VA-so-DI-la-tory) shock. It can occur due to:

• A severe head injury
• A reaction to certain medicines
• Liver failure
• Poisoning
• A severe allergic reaction (called anaphylactic (AN-a-fi-LAK-tik) shock)