When you have low blood oxygen levels, you can experience shortness of breath and confusion. Hypoxemia is a serious health condition that requires urgent medical care.

Hypoxemia is when you have low levels of oxygen in your blood. When this happens, the organs and tissues in your body don’t get enough oxygen to function properly.

Hypoxemia is often the result of a problem with gas exchange in your lungs, although it can have some other causes.

Gas exchange happens in the alveoli, the tiny air sacs in your lungs that are surrounded by blood vessels called capillaries.

During gas exchange, oxygen from the air you’ve breathed in passes from the alveoli into your blood and is then delivered to the cells throughout your body. While this is happening, carbon dioxide leaves your blood and moves into the alveoli, where it’ll be expelled when you exhale.

When this gas exchange is affected in some way, it can lead to hypoxemia. It’s a serious medical situation that requires prompt medical attention.

In this article, we’ll talk more about hypoxemia, including what causes it and how it’s treated.

Determining your blood oxygen level is an important part of diagnosing a variety of health conditions. There are different ways this can be done.

An arterial blood gas (ABG) test can measure the amount of oxygen and carbon dioxide in a blood sample taken from your artery, typically in your wrist. Arteries are blood vessels that carry oxygen-rich blood to the organs and tissues in your body.

Because the blood sample comes from an artery, the results of an ABG test can give your doctor an idea about the oxygen level of the blood that’s currently being delivered to your body’s tissues. It can also let them know how effectively carbon dioxide has been removed from your blood.

ABG test results
  • Values between 75 and 100 mm Hg are considered normal for an ABG test. When values fall below 75 mm Hg, you’re considered to have hypoxemia.
  • Another value reported by the ABG test is oxygen saturation. This is a measure of how much oxygen is being carried by hemoglobin on your red blood cells. Normal values for oxygen saturation are between 95 and 100 percent.

Pulse oximetry

You may also be familiar with pulse oximetry. This measures your blood oxygen levels using a device that you clip onto your finger. It reports oxygen saturation as a percentage. Pulse oximeters are generally less accurate than an ABG test.

For most people, a normal reading falls between 95 and 100 percent, although this may be lower if you have a known lung condition or live at a high elevation.

If you’re otherwise healthy and receive a reading of 92 percent or less on an at-home pulse oximeter, contact your doctor.

Someone with hypoxemia may experience the following symptoms:

Hypoxemia is a serious condition. Seek immediate medical attention if you or someone else is showing signs of hypoxemia.

There are many conditions that can cause hypoxemia. These include:

Hypoxemia can be caused in different ways. Let’s look at a couple of examples of conditions that can lead to hypoxemia:

  • Chronic obstructive pulmonary disease (COPD) is a chronic condition where the flow of air in the lungs is obstructed. With COPD, the destruction of the walls of the alveoli and surrounding capillaries can lead to problems with gas exchange which, in turn, can cause hypoxemia.
  • Anemia is a condition in which there aren’t enough red blood cells to effectively carry oxygen. Because of this, a person with anemia may have low levels of oxygen in their blood.

Additionally, hypoxemia can be a symptom of another condition like respiratory failure.

Respiratory failure occurs when not enough oxygen passes from your lungs to your blood. Therefore, low blood oxygen levels can be an indicator of respiratory failure.


Emphysema is a condition that falls under the umbrella of COPD. It causes harmful changes to the alveoli.

With emphysema, the walls of the alveoli become damaged, causing them to become weak, floppy, and less elastic. Because of this, they can’t fill up with air properly when you breathe in. This means that less oxygen is able to enter your blood during gas exchange.

Over time, the alveoli can also be destroyed. When this happens, it reduces the surface area of your lungs. This makes it harder to breathe and restricts how much oxygen can reach your bloodstream.

The most common cause of emphysema is long-term exposure to harmful gases, most often cigarette smoke. In fact, it’s estimated that 80 to 90 percent of people with COPD smoke cigarettes.

Other potential causes are long-term exposure to secondhand smoke or air pollution.

Hypoxemia in newborns

Hypoxemia can sometimes occur in newborns with congenital heart defects or disease. In fact, measuring the levels of oxygen in the blood is used to screen infants for congenital heart defects.

Preterm infants are also vulnerable to hypoxemia, particularly if they’ve been placed on a mechanical ventilator.

There are several different types of hypoxemia. These types are differentiated by the way in which blood oxygen levels are lowered.

Ventilation/perfusion (V/Q) mismatch

This is the most common type of hypoxemia. Ventilation refers to the oxygen supply in the lungs, while perfusion refers to the blood supply to the lungs.

Ventilation and perfusion are measured in a ratio called V/Q ratio. Normally, there’s a small degree of mismatch in this ratio, but problems can occur if the mismatch becomes too great.

There are two causes of ventilation-perfusion mismatch:

  1. The lungs are getting enough oxygen, but there’s not enough blood flow (increased V/Q ratio).
  2. There’s blood flow to the lungs, but not enough oxygen (decreased V/Q ratio).

Several conditions can lead to a V/Q mismatch, including but not limited to:

  • COPD
  • asthma
  • interstitial lung disease
  • fluid in the lung (pulmonary edema)
  • a blood clot in the lung (pulmonary embolism)


Normally, deoxygenated blood enters the right side of the heart, travels to the lungs to receive oxygen, and then travels to the left side of the heart to be distributed to the rest of the body.

With this type of hypoxemia, blood enters the left side of the heart without becoming oxygenated in the lungs. This leads to oxygen-depleted blood traveling to your body’s tissues.

Shunts can be caused by:

  • congenital heart defects or disease
  • a tangle of incorrectly formed blood vessels (arteriovenous malformations)
  • pneumonia
  • fluid in the lung (pulmonary edema)
  • acute respiratory distress syndrome (ARDS)

Diffusion impairment

As we discussed earlier, when oxygen enters the lungs, it moves to the alveoli, which are surrounded by tiny blood vessels called capillaries. This is where gas exchange takes place.

Oxygen typically diffuses from the alveoli into the blood running through the capillaries. In this type of hypoxemia, the diffusion of oxygen into the bloodstream is impaired.

Some potential causes of diffusion impairment include:

  • interstitial lung disease
  • scarring in the lungs (pulmonary fibrosis)
  • fluid in the lung (pulmonary edema)
  • COPD, specifically emphysema


Hypoventilation is when oxygen intake occurs at a slow rate. This can result in higher levels of carbon dioxide in the blood and lower oxygen levels.

Hypoventilation can happen due to things like:

Low environmental oxygen

This type of hypoxemia typically occurs at higher altitudes. Oxygen in the air decreases with increasing altitude. Therefore, at higher altitudes, each breath you take provides you with lower oxygen levels than when you’re at sea level.

In order to diagnose hypoxemia, your doctor will perform a physical examination during which they’ll check your heart and lungs. They may also check the color of your skin, fingernails, or lips.

There are some additional tests that can be used to assess your oxygen levels and breathing. These include:

  • pulse oximetry, which uses a device placed on your finger to measure blood oxygen levels
  • arterial blood gas test, which uses a needle to draw a blood sample from an artery to measure blood oxygen levels
  • pulmonary function tests, which are breathing tests that evaluate your breathing through a machine or by breathing into a tube
  • imaging, like a chest x-ray, which can help your doctor look for potential causes of hypoxemia, like pneumonia or fluid in the lungs

Since hypoxemia involves low blood oxygen levels, the aim of treatment is to try to raise blood oxygen levels back to normal.

Oxygen therapy can be utilized to treat hypoxemia. This may involve using an oxygen mask or a small tube clipped to your nose to receive supplemental oxygen.

Hypoxemia can also be caused by an underlying condition like asthma or pneumonia. If an underlying condition is causing your hypoxemia, your doctor will work to treat that condition as well.

The organs and tissues of your body require oxygen in order to function properly.

Damage can occur to vital organs like your heart and brain in the absence of enough oxygen. Hypoxemia can be fatal if it goes untreated.

It’s not possible to prevent all cases of hypoxemia. But there are some steps you can take to lower your risk of this condition:

  • Manage your health conditions. If you have a health condition that can potentially cause hypoxemia, like asthma or sleep apnea, ensure that it’s being properly managed or treated.
  • Stop smoking. Smoking can damage your lungs and is a risk factor for many health conditions. If you currently smoke, it’s not too late to quit. Talk with your doctor about how to get started on a quit plan.
  • Avoid exposure to air pollution. Long-term exposure to pollutants like secondhand smoke or chemical fumes can harm your lungs. If you work in an environment where you’re exposed to harmful fumes, be sure to wear a face mask or other protective device.
  • Prevent infections. A variety of infections can lead to pneumonia, which can cause hypoxemia. Take steps to prevent infections by washing your hands, avoiding people who are sick, and getting the appropriate vaccinations. Vaccinations that can prevent pneumonia include the:
  • Make healthy lifestyle choices. Trying to adopt healthy lifestyle habits can improve your health and reduce your risk of some health conditions that can cause hypoxemia. Examples of healthy lifestyle choices include:

Hypoxia and hypoxemia refer to two different things. While hypoxemia refers to low oxygen levels in your blood, hypoxia refers to low levels of oxygen in the tissues of your body.

The two can sometimes, but not always, occur together. For example, hypoxia can happen in the absence of hypoxemia if blood flow to an organ or tissue is disrupted. In this case, the blood may have normal levels of oxygen, but it can’t reach the affected area.

Generally, the presence of hypoxemia suggests hypoxia. This makes sense because if oxygen levels are low in your blood, the tissues of your body are also probably not getting enough oxygen either.

You should always seek emergency medical attention if shortness of breath happens suddenly and makes it hard for you to breathe.

Make an appointment with your doctor if you experience any of the following symptoms:

  • shortness of breath that occurs with minimal activity or when you’re at rest
  • shortness of breath that occurs with exercise and gets worse
  • waking suddenly from sleep with shortness of breath

Hypoxemia is when you have low levels of oxygen in your blood. There are several different types of hypoxemia and many different conditions can cause it.

Hypoxemia is a serious condition and can lead to organ damage or even death if left untreated.

You should always seek emergency medical care if you have shortness of breath that occurs suddenly and affects your ability to function or breathe properly.