Definition

Hypoxemia is a below-normal level of oxygen in your blood, specifically in the arteries. Hypoxemia is a sign of a problem related to breathing or circulation, and may result in various symptoms, such as shortness of breath.

Hypoxemia is determined by measuring the oxygen level in a blood sample taken from an artery (arterial blood gas). It can also be estimated by measuring the oxygen saturation of your blood using a pulse oximeter — a small device that clips to your finger.

Normal arterial oxygen is approximately 75 to 100 millimeters of mercury (mm Hg). Values under 60 mm Hg usually indicate the need for supplemental oxygen. Normal pulse oximeter readings usually range from 95 to 100 percent. Values under 90 percent are considered low.

Causes

Several factors are needed to continuously supply the cells and tissues in your body with oxygen:

• There must be enough oxygen in the air you are breathing
• Your lungs must be able to inhale the oxygen-containing air — and exhale carbon dioxide
• Your bloodstream must be able to circulate blood to your lungs, take up the oxygen and carry it throughout your body

A problem with any of these factors — for example, high altitude, asthma or heart disease — might result in hypoxemia, particularly under more extreme conditions, such as exercise or illness. When your blood oxygen falls below a certain level, you might experience shortness of breath, headache, and confusion or restlessness.

Common causes of hypoxemia include:

• Anemia
• ARDS (Acute respiratory distress syndrome)
• Asthma
• Congenital heart defects in children
• Congenital heart disease in adults
• COPD (chronic obstructive pulmonary disease) exacerbation — worsening of symptoms
• Emphysema
• Interstitial lung disease
• Medications, such as certain narcotics and anesthetics, that depress breathing
• Pneumonia
• Pneumothorax (collapsed lung)
• Pulmonary edema (excess fluid in the lungs)
• Pulmonary embolism (blood clot in an artery in the lung)
• Pulmonary fibrosis (scarred and damaged lungs)
• Sleep apnea

When to see a doctor

Seek emergency care if you have:

• Severe shortness of breath that comes on suddenly and affects your ability to function.
• Severe shortness of breath with a cough, rapid heartbeat and fluid retention at high elevations (above 8,000 feet, or about 2,400 meters). These are signs and symptoms of fluid leaking from blood vessels into your lungs (high-altitude pulmonary edema), which can be fatal.

See your doctor as soon as possible if you have:

• Shortness of breath after slight exertion or when you're at rest
• Shortness of breath that gets worse when you exercise or are physically active
• Abrupt awakenings with shortness of breath or a feeling that you're choking — these may be symptoms of sleep apnea

Self-care

To cope with chronic shortness of breath, try to:

• Stop smoking. If you've been diagnosed with COPD or another lung disease, the single most important thing you can do is to quit smoking.
• Avoid passive smoke. Avoid places where others smoke. Secondhand smoke can cause further lung damage.
• Get regular exercise. It may seem difficult to exercise when you have trouble breathing, but regular exercise can improve your overall strength and endurance.