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Key takeaways
Hypoxemia is characterized by low oxygen content in the blood, while hypoxia refers to low oxygen supply in bodily tissues, and although they often co-occur, their causes, symptoms, and treatments can vary.
Common causes of both conditions include asthma, lung conditions, heart disease, anemia, and environmental factors like high altitude, with COVID-19 also emerging as a cause of “silent hypoxemia.”
Symptoms of hypoxia and hypoxemia are similar and may include shortness of breath, coughing, wheezing, headache, rapid heartbeat, confusion, and cyanosis, with severe cases potentially leading to respiratory failure or coma.
Treatment for both conditions often involves oxygen therapy and mechanical ventilation, and prevention includes managing pre-existing health conditions, avoiding smoking, and maintaining a healthy lifestyle.
Hypoxia vs. hypoxemia causes | Prevalence | Symptoms | Diagnosis | Treatments | Risk factors | Prevention | When to see a doctor | FAQs | Resources
Blood is the body’s hyper-efficient transportation system, and it deals in two primary commodities: nutrients and oxygen. Organs and muscles need both to operate, so a deficiency of either nutrients or oxygen can cause health issues. Hypoxia and hypoxemia both concern the body’s oxygen levels. Because they have similar spellings, these two conditions are often confused. While they can co-occur, they’re fairly different.
In short, hypoxemia refers to low oxygen content in the blood, whereas hypoxia means low oxygen supply in bodily tissues. In many cases, hypoxemia points to hypoxia since low oxygen concentration in the blood often affects oxygen delivery to the tissues. They can also have similar symptoms, making the two even more difficult to discern. That’s where this guide comes in handy. It’s an in-depth look at hypoxia vs. hypoxemia, everything from causes to treatments, to distinguish between them.
Causes
Hypoxia
Any condition or event that reduces oxygen intake can reduce the amount of oxygen in bodily tissues. Causes of hypoxia include:
- Asthma attacks and lung diseases. These conditions commonly cause hypoxia since they directly restrict oxygen supply.
- Ineffective oxygen transport. Heart diseases that affect cardiac output can inhibit blood flow and anemia (caused by low levels of healthy red blood cells) can reduce the amount of oxygen that blood can deliver.
- Coronavirus (COVID-19). More recently, the novel coronavirus has emerged as another common cause.
- Low oxygen concentration in the surrounding air. High altitudes might be a cause of hypoxia, especially for individuals with pre-existing risk factors.
- Carbon monoxide or cyanide. Poisoning by carbon monoxide or cyanide in a person’s environment can cause sudden hypoxia without hypoxemia.
Hypoxemia
There are five main causes of hypoxemia: not enough blood flow or oxygen to the lungs (ventilation-perfusion mismatch), blood entering the left side of the heart without being oxygenated first (right-to-left shunting), impaired movement of oxygen from the lungs into the bloodstream (diffusion impairment), shallow and ineffective breathing (hypoventilation), and low environmental oxygen. The underlying factors that can cause hypoxemia are relatively similar to those that cause hypoxia. For this reason, the causes of hypoxemia and hypoxia can overlap. Essentially, anything that reduces the ability to intake oxygen or oxygenate the blood can be a cause. Other causes of hypoxemia include:
- Asthma attacks
- Lung diseases
- Heart diseases
- Anemia
- High altitude
- Lung trauma
- Recently, COVID-19 has been causing a phenomenon called “silent hypoxemia” or “happy hypoxia,” in which a patient shows little to no symptoms but still has low blood oxygen levels.
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Prevalence
There are a few studies on the prevalence of hypoxia or hypoxemia in specific situations, but none on the general rate of occurrence in the U.S. at any given time.
Symptoms
Hypoxia
The symptoms of hypoxia can vary based on the condition’s cause and severity. Generally, they include coughing, wheezing, increased heart rate, headache, and a bluish color in the skin, lips, or fingernails (called cyanosis). Severe cases might even cause fainting or seizures. In the case of cerebral hypoxia (low oxygen in the brain), a person might experience confusion, difficulty speaking, temporary memory loss, difficulty moving, or coma.
Chronic or less severe cases of hypoxia can cause general fatigue and shortness of breath, especially after physical activity.
Hypoxemia
Since both of these conditions deal with a lack of oxygen, they have similar symptoms too. People with hypoxemia may experience shortness of breath, coughing, wheezing, headache, rapid heartbeat, confusion, and cyanosis. Severe cases can also cause hypoxemic respiratory failure, characterized by low blood oxygen levels but normal carbon dioxide levels.
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Hypoxia diagnosis
As long as the patient isn’t in distress, a doctor will typically start with a physical exam to evaluate the heart and lungs. If they recognize signs of hypoxia, they will likely move on to other tests. Pulse oximetry is a non-invasive test where the doctor uses a fingertip sensor to measure blood oxygen levels. An arterial blood gas test uses a blood sample to measure the partial pressure of oxygen (PaO2), oxygen saturation, the partial pressure of carbon dioxide, and blood pH levels.
If the doctor suspects cerebral hypoxia, they might also order an MRI, CT scan, echocardiogram, or electroencephalogram (EEG).
Hypoxemia
Tests for hypoxemia are mostly the same. They usually involve a physical exam, followed by pulse oximetry or arterial blood gas tests. Lung function tests, which measure the amount of air inhaled and exhaled, plus oxygen delivery efficiency, can also help confirm a diagnosis.
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Hypoxia treatments
The most common hypoxia treatment is oxygen therapy, which provides supplemental oxygen via a face mask or tubes placed in the nose or trachea. In severe cases, mechanical ventilation might also be necessary. To support heart function, a doctor might also give their patient intravenous fluids or medications to raise blood pressure or curb seizures (especially in cases of cerebral hypoxia).
Hypoxemia
Similarly, oxygen therapy and mechanical ventilation are the most common treatments for hypoxemia. Doctors might also prescribe medication using an inhaler to assist with breathing.
Depending on the cause, it might also be necessary to get to the root of hypoxemia by treating an underlying condition, such as pneumonia or emphysema. Doctors may prescribe antibiotics or steroids to treat these underlying conditions.
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Risk factors
Any pre-existing condition that reduces oxygen intake or prevents oxygen transport can increase the risk of hypoxia. So, people who have asthma, COPD, emphysema, bronchitis, or other lung diseases are at higher risk. Experiencing frequent altitude changes, like airline pilots and staff do, may also result in a higher chance of hypoxia. Given its detrimental effects on the lungs, smoking is also a significant risk factor.
Heart disease can inhibit oxygen delivery (and vice versa), which can increase the risk of hypoxia. Other factors associated with heart disease such as obesity, high cholesterol, and a family history of heart disease may also contribute to hypoxia risk.
Hypoxemia
Hypoxemia has many of the same risk factors. Any condition that prevents the body from getting enough oxygen can potentially cause it. Conditions include pre-existing lung diseases like asthma, COPD, emphysema, and bronchitis, as well as environmental changes like altitude and carbon monoxide inhalation. Lifestyle habits that can cause lung and heart issues—like smoking, unhealthy diet, and inactivity—may also put someone at a higher risk of developing hypoxemia.
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Prevention
Hypoxia
Preventing hypoxia requires managing chronic health conditions, avoiding lifestyle risk factors, and being aware of the environment. Someone with severe asthma or COPD will want to take prescribed medications consistently and schedule regular doctor visits. Someone who smokes and/or is physically sedentary will want to quit smoking and increase their physical activity.
Hypoxemia
Again, prevention mostly consists of getting treatment for underlying conditions and making healthy lifestyle decisions.
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When to see a doctor about hypoxia or hypoxemia
Both conditions are serious. Restricting tissue oxygenation, especially in the organs and the brain, can have serious consequences. Anyone who experiences a sudden and/or severe shortness of breath, specifically when it inhibits their ability to function normally, should seek help from a health care professional. Shortness of breath that occurs during rest or inactivity (or in the middle of the night) is particularly concerning. A person with pre-existing lung conditions or other risk factors should visit a doctor immediately if they experience the symptoms listed above.
Frequently asked questions about hypoxia and hypoxemia
Does pulse oximetry measure hypoxia or hypoxemia?
Pulse oximetry is a noninvasive test that measures blood oxygen saturation. It can directly detect hypoxemia. Blood oxygen levels can be a direct indicator of tissue oxygenation, so pulse oximetry can diagnose hypoxia as well.
Are hypoxia and hypoxemia the same?
No, but they’re closely related. Hypoxemia is characterized by low oxygen content in the blood, while hypoxia means low oxygen content in bodily tissues. Because blood flow delivers oxygen to tissues, hypoxemia can suggest or cause hypoxia, and the two often occur together.
What are the clinical signs of hypoxia vs. hypoxemia?
The clinical signs of hypoxia and hypoxemia are similar. Both conditions can cause shortness of breath, coughing, wheezing, headache, confusion, and skin discoloration. Cerebral hypoxia (low oxygen in the brain) can also cause trouble speaking, temporary memory loss, reduced movement, and coma.