When Is Low Blood Pressure an Emergency? An ER Doctor Explains the Potential Dangers

Low blood pressure readings don’t cause as much concern as high blood pressure. But healthcare professionals — especially ER doctors and nurses — want you to think again. 

In fact, most often, low blood pressure is much more worrisome than high blood pressure when it comes to an immediate life threat. Here, we explain why it’s dangerous, and how to know when it’s time to go to the ER for low blood pressure 

What’s considered low blood pressure?

Low blood pressure — also referred to as hypotension — is when blood pressure readings are less than:

• 90 mmHg systolic blood pressure (the top number)

• 60 mmHg diastolic blood pressure (the bottom number)

Every time your heart pumps, the flow of blood exerts a force on the walls of your blood vessels. Blood pressure is the measure of this force. The top number measures that force as the heart is actively squeezing, pushing blood forward. The bottom number measures the force when the heart is relaxed and filling back up, and so the blood is at a relative standstill. 

So blood pressure depends on the amount of blood and fluid in the blood vessels, and how hard they’re squeezing. A problem with either can cause low blood pressure.

What are the emergent causes of low blood pressure?

There are many causes of low blood pressure. Many of them are serious medical conditions that need to be treated sooner rather than later. Some people have low blood pressure naturally, but this isn’t very common. 

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Below we describe some of the most common causes of low blood pressure.

Dehydration 

Dehydration can range from mild to severe. It can be caused by:

• Not drinking or eating enough

• Prolonged exposure to warm temperatures

• Heavy exercise 

• Vomiting and diarrhea 

• High blood sugar, which makes you pee a lot more than normal

• Certain medications, like diuretics or laxatives

Most types of dehydration will lead to at least mild drops in blood pressure. But in the next section, we’ll go through symptoms that help you know if it’s getting into the severe range. 

Severe bleeding 

Low blood pressure from bleeding isn’t always obvious, and it doesn’t necessarily happen with one bleeding episode. Different types of internal bleeding can produce mild or vague symptoms when it first starts. For example, slow blood loss over time in the gastrointestinal tract might not cause any noticeable changes to your bowel movements. But it can still lead to critically low blood counts and low blood pressure. 

Sepsis 

Sepsis is a medical complication of a severe infection. It happens when the immune system becomes overwhelmed by the infection, and produces chemicals in the body that can drop someone’s blood pressure. This is one of the more threatening causes of low blood pressure, and it can progress quickly. 

Heart failure 

If the heart can’t squeeze as well as it needs to, it might not be able to create enough blood pressure to keep blood moving through the blood vessels. Also, leaky heart valves can make it challenging for the heart to work properly, resulting in low blood pressure.

This can happen to people with known heart failure (or valve problems) if they start to get worse. But it can also happen abruptly if someone has a heart attack that goes unnoticed. Or a new diagnosis of atrial fibrillation that’s preventing the heart from getting a good squeeze.

Allergic reactions 

Severe allergic reactions — called anaphylaxis — can lead to low blood pressure. Common symptoms of anaphylaxis include hives and swelling of the mouth, tongue, or throat. But without quick intervention (an EpiPen), it can cause all your blood vessels to dilate. This can lead to a rapid and dangerous drop in blood pressure. This is what people refer to when they say “anaphylactic shock.” 

Medication side effects 

Many people take medications for high blood pressure and heart disease. But many of these medications can lead to low blood pressure if:

• The dose is too high, or you accidentally take too much.

• It interacts with another medication that causes low blood pressure.

• Your blood pressure is running lower than normal on that particular day.

Why is low blood pressure dangerous?

Low blood pressure — especially when it’s not brief or temporary — is dangerous because it affects oxygen delivery to vital organs.

Blood carries oxygen and vital nutrients to all the different parts of your body. Even though high blood pressure over the long term can be bad for your health, it doesn’t mean that the lower it is, the better. There still needs to be some pressure in the blood vessels for the blood to flow. If blood pressure is too low, blood will not reach all of the organs to deliver these vital nutrients. 

This can be dangerous for many reasons, including:

• Organ damage: Many organs in the body will quickly become damaged when they’re deprived of oxygen. And in severe cases, the organ can start to fail. This is why low blood pressure is often a medical emergency.

• Loss of consciousness: When your blood pressure is low, it can be hard to get blood up into the brain. This can cause lightheadedness, dizziness, or even full loss of consciousness (fainting). This can result in serious injuries.

• Falls: Even in the absence of dizziness or fainting, low blood pressure often makes people feel weak or off balance. This can also lead to falls, especially in older adults. 

And last but not least, low blood pressure is dangerous because it can also be a sign of one of the serious underlying illnesses from above. So it’s important to take it seriously, and know when it’s time to go to the ER.

What are the worrisome symptoms of low blood pressure?

The symptoms of low blood pressure come from not getting enough blood to the organs of the body. These symptoms include:

• Lightheadedness: A common symptom of low blood pressure is a lightheaded feeling, particularly with position changes. This is from the brain not receiving enough blood.

• Passing out: If the drop in blood flow to the brain is severe, people might lose consciousness. 

• Confusion: Even without changes in consciousness, people might have a hard time thinking or acting normally from lack of blood flow to the brain.

• Blurry vision or tunnel vision: This can happen from lack of blood flow to the brain or the eyes.

• Diffuse weakness: You might feel overwhelmingly weak or tired.

• Heart pounding or palpitations: When the blood pressure drops, the heart may work harder to try to keep the blood flowing. You might feel your heart pounding strongly as a result.

• Chest pain: Some people with coronary artery disease or heart failure may already have lower blood flow to the heart muscle. So a further drop in blood pressure may further limit oxygen getting to the heart muscle, and cause angina. 

• Nausea and/or vomiting: Sudden drops in blood pressure often make people feel nauseous from lack of blood flow to the stomach. This may accompany a feeling like you’re going to pass out, or happen on its own. 

• Changes in urine: Lack of blood flow to the kidneys can lead to a significant drop in the amount of urine, or very dark-colored urine.

When to go to the ER for low blood pressure

The short answer is almost always. As we mentioned in the sections above, low blood pressure is dangerous. Not only because it can be a sign of a life-threatening health condition. But also because hypotension itself can cause problems, regardless of the cause.

Some people may have low blood pressure normally. If you know that your blood pressure runs low and you’re feeling normal, you could call your primary care provider to ask for their advice. 

You should go to the ER for low blood pressure if you have low blood pressure and:

• You usually have a normal (or even high) blood pressure on most days.

• Low blood pressure lasts several hours and it’s not improving. 

• You have any of the symptoms above alongside your low blood pressure.

• You have abnormally high heart rate (over 100 beats per minute or bpm) or low heart rate (below 50 bpm) for unexplained reasons.

• You experience any symptoms of an infection, like pneumonia, urinary tract infection, or skin infection.

• You have severe abdominal pain or blood in your stool.

• You have severe vomiting or diarrhea, and cannot keep anything down.

• You experience signs of an allergic reaction.

• You have heart failure and you feel you’re retaining fluid.

It’s also important to go straight to the ER rather than an urgent care. This is the best place to get quick treatment for low blood pressure.

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Written by:

Michael Dreis, MD

Dr. Dreis is an emergency medicine physician currently practicing in Milwaukee, Wisconsin. He went to medical school at the University of Wisconsin – Madison and completed his residency at Henry Ford Hospital in Detroit, Michigan.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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