Low blood oxygen (hypoxemia)

Definition

Hypoxemia is a low level of oxygen in the blood. It starts in blood vessels called arteries. Hypoxemia isn't an illness or a condition. It's a sign of a problem tied to breathing or blood flow. It may lead to symptoms such as:

• Shortness of breath.
• Rapid breathing.
• Fast or pounding heartbeat.
• Confusion.

A healthy level of oxygen in the arteries is about 75 to 100 millimeters of mercury (mm Hg). Hypoxemia is any value under 60 mm Hg. Levels of oxygen and the waste gas carbon dioxide are measured with a blood sample taken from an artery. This is called an arterial blood gas test.

Most often, the amount of oxygen carried by red blood cells, called oxygen saturation, is measured first. It is measured with a medical device that clips to the finger, called a pulse oximeter. Healthy pulse oximeter values often range from 95% to 100%. Values under 90% are considered low.

Often, hypoxemia treatment involves receiving extra oxygen. This treatment is called supplemental oxygen or oxygen therapy. Other treatments focus on the cause of hypoxemia.

Causes

You might learn you have hypoxemia when you see a doctor for shortness of breath or another breathing-related problem. Or you might share the results of an at-home pulse oximetry test with your doctor.

If you use a pulse oximeter at home, be aware of factors that can make the results less accurate:

• Poor circulation.
• Black or brownskin color.
• Skin thickness or temperature.
• Tobacco use.
• Fingernail polish.

If you have hypoxemia, the next step is to figure out its cause.

Hypoxemia can be a sign of problems such as:

• Less oxygen in the air you breathe, such as at high altitudes.
• Breathing that's too slow or shallow to meet the lungs' need for oxygen.
• Either not enough blood flow to the lungs or not enough oxygen to the lungs.
• Trouble with oxygen getting into the bloodstream and the waste gas carbon dioxide getting out.
• A problem with the way blood flows in the heart.
• Unusual changes in the protein called hemoglobin, which carries oxygen in red blood cells.

Causes of hypoxemia that are related to problems with blood or blood flow include:

• Anemia
• Congenital heart defects in children — heart conditions that children were born with.
• Congenital heart disease in adults — heart problems that adults were born with.

Breathing conditions that can lead to hypoxemia include:

• ARDS (acute respiratory distress syndrome) — a lack of air due to a buildup of fluid in the lungs.
• Asthma
• COPD
• Interstitial lung disease — the blanket term for a large group of conditions that scar the lungs.
• Pneumonia
• Pneumothorax — collapsed lung.
• Pulmonary edema — excess fluid in the lungs.
• Pulmonary embolism
• Pulmonary fibrosis — a disease that happens when lung tissue becomes damaged and scarred.
• Sleep apnea — a condition in which breathing stops and starts many times during sleep.

Some medicines that can cause slow, shallow breathing can lead to hypoxemia. These include certain opioid pain relievers and medicines that prevent pain during surgery and other procedures, called anesthetics.

When to see a doctor

Seek emergency care if you have shortness of breath that:

• Comes on fast, affects your ability to function or happens with symptoms such as chest pain.
• Happens above 8,000 feet (about 2,400 meters) and occurs with a cough, rapid heartbeat or weakness. These are symptoms of fluid leaking from blood vessels into the lungs, called high-altitude pulmonary edema. This can be deadly.

See your doctor as soon as possible if you:

• Become short of breath after slight physical effort or when you're at rest.
• Have shortness of breath that you wouldn't expect from a certain activity and your current fitness and health.
• Wake up at night with a gasp or a feeling that you're choking. These may be symptoms of sleep apnea.

Self-care

These tips could help you cope with ongoing shortness of breath:

• If you smoke, quit. This is one of the most important things you can do if you have a health condition that causes hypoxemia. Smoking makes medical problems worse and harder to treat. If you need help quitting, talk with your health care provider.
• Stay away from secondhand smoke. It can cause more lung damage.
• Get regular exercise. Ask your provider what activities are safe for you. Regular exercise can boost your strength and endurance.