This article will cover the various causes of low blood pressure, possible symptoms, and treatment options.

Symptoms

Blood pressure is measured in millimeters of mercury (mmHg). Hypotension is usually defined as a systolic (upper) value of 90 mmHg and a diastolic (lower) value of 60 mmHg. Normal blood pressure is considered 120/80 mmHg or below.

However, blood pressure that’s too far below that number can lead to problems. Generally speaking, the lower and faster the blood pressure drops, the more severe the symptoms will be. The extent of the drop in pressure also plays a role.

For example, if you have high blood pressure (hypertension) and the pressure suddenly drops to below 90/60 mmHg, you are more likely to experience noticeable symptoms than if it were to drop from, say, 110/70 mmHg.

Sudden (also called acute) drops in blood pressure can cause symptoms ranging from mild lightheadedness and fatigue to severe heart rhythm problems and respiratory distress.

Common Symptoms

When blood pressure drops suddenly, blood flow to the body decreases. This starves the body of the oxygen and nutrients that it needs to function. The lack of blood flow to the brain especially triggers symptoms.

Common signs include:

LightheadednessDizzinessNauseaFatigueSleepinessDifficulty concentratingBlurred visionFainting

Other symptoms that can occur include chest pain, shortness of breath, irregular heartbeat, hives, fever, indigestion, and vomiting. These tend to be associated with the condition that caused the drop in the first place.

Severe Symptoms

Extreme hypotension can severely deprive the brain and vital organs of oxygen and nutrients, leading to shock. Shock can progress rapidly. Symptoms include:

Extreme weaknessExtreme anxietyRapid heart rateWeak pulseRapid, shallow breathingProfuse sweatingIncreased thirstCold, clammy skinConfusion

Causes

There are several possible causes of hypotension. Some of them can overlap, making the diagnosis more difficult. Causes include:

Hypovolemia

Hypovolemia is a term used to describe reduced blood volume. This is the most common cause of hypotension. It can occur if you are not getting enough fluids or if your body is losing too much fluid.

Common causes of hypovolemia include:

DehydrationBlood loss, leading to hemorrhagic shockStarvation or fastingSevere diarrhea or vomitingHeatstrokeExcessive use of diuretics (“water pills”)Kidney failureSevere pancreatitis (causing the leakage of fluid into the abdominal cavity)

Decreased Cardiac Output

Even if your blood volume is normal, there are conditions that can reduce the body’s ability to pump blood. This condition is known as decreased cardiac output.

It can occur as a result of a heart problem, endocrine (hormonal) dysfunction, and certain medications. Sudden changes in cardiac output can cause a sudden drop in blood pressure.

Causes of decreased cardiac output include.

Congestive heart failure (CHF) Coronary artery disease (CAD) Myocardial infarction (heart attack) Heart valve disease, including aortic stenosis Bradycardia (abnormally slow heart rate) Drugs like alpha-blockers and beta-blockers that can slow heart rate Endocrine disorders such as hypothyroidism, hypoparathyroidism, Addison’s disease, and hypoglycemia (which indirectly affects heart function)

Vasodilation

Vasodilation describes the sudden widening of blood vessels. As the blood vessels get wider, blood pressure continues to drop.

Common causes of vasodilation include:

Vasodilating drugs: Drugs in this category include calcium channel blockers, angiotensin II receptor blockers, nitroglycerin, nitrous oxide, Rogaine (minoxidil), and Viagra (sildenafil). Dysautonomia: A condition in which which the autonomic nervous system malfunctions, affecting the heart, bladder, intestines, blood vessels, and other organs Sepsis: A life-threatening reaction to an infection Anaphylaxis: A severe, whole-body allergy that can lead to anaphylactic shock Acidosis: A condition in which blood acids are elevated Neurogenic shock: Shock caused by a brain or spinal cord injury

Hypotensive Syndromes

A hypotensive syndrome is the term used when more than one factor causes a sudden drop in blood pressure. Usually the person has an underlying condition that is then triggered by doing something such as standing up after sitting or experiencing severe emotional distress.

Hypotensive syndromes tend to come on suddenly, sometimes with dramatic symptoms, including extreme dizziness and unconsciousness.

Some common hypotensive syndromes include:

Neurogenic orthostatic hypotension (NOH) is when a change in body position, such as rising from a chair or bed, causes a dramatic drop in blood pressure. NOH is caused by an underlying neurologic disorder that affects the autonomic nervous system. It is common with neurodegenerative disorders like Parkinson’s disease and Lewy body dementia as well as diabetic nerve damage. Orthostatic hypotension (OH) has the same symptoms as NOH. It is brought on by non-neurologic causes such as decreased cardiac output and extreme vasodilation. Drugs such as diuretics, tricyclic antidepressants, and medications for high blood pressure can also cause OH. Supine hypotensive syndrome occurs in later pregnancy when the weight of the baby presses down on two of the largest blood vessels in the body, the aorta and the inferior vena cava. This decreases the flow of blood to the heart. Postprandial hypotension occurs after eating. Blood is diverted to the intestines to help digestion. This temporarily robs the brain of blood and oxygen. It is most common in the elderly and generally occurs within 30 to 75 minutes of eating. Vasovagal syncope is an overreaction to certain triggers, such as the sight of blood or extreme emotional distress. This leads to a steep drop in blood pressure and fainting (syncope). It is caused by the overactivation of the vagus nerve, which relays nerve signals from the heart, liver, lungs, and gut to the brain. Situational reflex syncope affects the vagus nerve. It can occur when physical stress is placed directly on the nerve. Straining during a bowel movement, lifting a heavy weight, or standing for too long in one place can cause this to happen. Urinating after taking a vasodilating drug like Cialis (tadalafil) can also trigger reflex syncope. Carotid artery syncope involves the compression of the internal carotid artery of the neck. Wearing a tight collar, shaving, or turning the head can cause a sudden drop in blood pressure, especially in older people or those with carotid artery stenosis.

Diagnosis

A blood pressure cuff called a sphygmomanometer can tell you how low your blood pressure is, but it can’t tell you what caused the sudden drop.

For this, the doctor will need to review your medical history, family history, current symptoms, and medications. Then they will perform some of the following tests to figure out the cause:

Valsalva maneuver: An in-office test used to diagnose orthostatic hypotension. You blow hard through pursed lips to see how it affects your blood pressure and heart rate. Blood tests: Blood test results can reveal conditions associated with acute hypotension. These include diabetes, anemia, hypoglycemia, thyroid problems, kidney problems, and hormonal imbalances. Urinalysis: A urine test can help diagnose kidney disease. Electrocardiogram (ECG): An ECG measures electrical activity in the heart to detect rhythm disorders, heart failure, and other cardiovascular problems. Echocardiogram: This test uses sound waves to create video images of the heart to detect structural defects like heart valve leakage. Imaging tests: Computed tomography (CT), magnetic resonance imaging (MRI), and X-rays are used to detect internal bleeding, structural heart problems, kidney problems, or a brain or spinal cord injury. Tilt table testing: This measures heart function and blood pressure as the body is tilted at different angles on an adjustable table. It is mostly used to diagnose postural hypotension. Stress testing: A stress test measures a person’s heart function and blood pressure while they are running on a treadmill or pedaling a stationary bike. It is primarily used to diagnose coronary artery disease.

Treatment

The treatment of acute hypotension varies based on the underlying cause. If the condition is not a medical emergency, you should either sit or lie down immediately and raise your feet above heart level. If you are dehydrated, you should replenish lost fluids and seek immediate medical attention if the symptoms are severe.

If hypovolemic or hemorrhagic shock is involved, you may be given an intravenous (IV) saline solution or a blood transfusion. Septic shock may require IV antibiotics, while anaphylactic shock requires epinephrine (adrenaline).

If hypotension is related to extreme vasodilation or decreased cardiac output, medications such as vasodilators (like midodrine) or drugs to stimulate the heart (like digitalis) may be prescribed to improve heart function and output.

People with severe postural hypotension may benefit from the use of the anti-inflammatory steroid fludrocortisone.

Summary

A sudden drop in blood pressure can occur for a variety of reasons. Some of these are not serious. In some cases, though, it may be a sign of something more serious, and even life-threatening. Serious underlying causes usually have other symptoms.

Hypotension can often be treated successfully. The underlying cause, on the other hand, may require extensive treatment by a specialist, such as a cardiologist, neurologist, or endocrinologist.

A Word From Verywell

It is important not to ignore signs of hypotension. This is especially true if the drop is sudden and severe. By seeing a doctor and pinpointing the cause of acute hypotension, you can be treated appropriately and avoid any long-term harm to your health.