What is Hypoxemia & How Does It Differ From Hypoxia?|Types, Causes, Symptoms, Treatment of Hypoxemia

Your body needs oxygen to survive and continue living. When you fail to get enough oxygen, you are likely to get hypoxemia or hypoxia. Both of these are dangerous conditions because, without sufficient oxygen, your brain, your kidneys, your liver, and all other organs might be damaged – even by just minutes before your symptoms start to show. Your blood is responsible for carrying oxygen to all the organs and tissues of your body, and if there are low levels of oxygen in the blood, you might develop hypoxemia. There is a lot of confusion between hypoxemia and hypoxia. Hypoxemia is low oxygen levels in your blood while hypoxia is low oxygen levels in your tissues. It is possible for hypoxemia to cause hypoxia. But typically the word hypoxia itself is used to describe both these problems. Let us take a closer look at what is hypoxemia and how does it differ from hypoxia.

What is Hypoxemia?

What is Hypoxemia?

Hypoxemia is a condition that is marked by the lack of oxygen in your blood, which can cause the condition of hypoxia, a condition characterized by low oxygen in your tissues.

Hypoxemia can be caused by many conditions, including chronic obstructive pulmonary disease (COPD), asthma, and pneumonia. It is a serious medical condition, and you need to seek urgent medical attention.

How Does Hypoxemia Differ From Hypoxia?

There is a lot of confusion between the two terms, and many times, both the conditions are simply referred to as hypoxia. However, hypoxemia and hypoxia are two different things. While hypoxemia is related to the low oxygen levels in your blood, hypoxia refers to having low oxygen in the tissues of your body.

While sometimes the two conditions can occur together, it is not always the case.

Usually, though, the presence of hypoxemia does tend to suggest hypoxia. This is understandable because if there is a low level of oxygen in the bloodstream, then, of course, the tissues of the body are also not going to get enough oxygen.(1)

Types of Hypoxemia

There are many types of hypoxemia, and the exact kind of hypoxemia depends on the mechanism due to which the oxygen levels in the blood are lowered.
Here are some of the more common types of hypoxemia:

V/Q Mismatch (Ventilation/Perfusion)

V/Q mismatch is the most common type of hypoxemia that is observed. The oxygen supply present in the lungs is referred to as ventilation, while the blood supply to the lungs is referred to as perfusion.

Both ventilation and perfusion are measured in a ratio that is referred to as the V/Q ratio. Typically there is a small degree of a mismatch that exists in this ratio. However, when this mismatch becomes too high, then problems start occurring.

There are two known causes of ventilation/perfusion mismatch. These are:

  • Your lungs are not getting sufficient oxygen, but there is not adequate blood flow. In this scenario, there is an increase in the V/Q ratio.
  • There is proper blood flow to the lungs, but there is not enough oxygen reaching the lungs. In this scenario, there is a decrease in the V/Q ratio.

Diffusion Impairment

Diffusion impairment is also another type of hypoxemia, in which the process of oxygen diffusion into the blood gets disrupted or impaired.

When oxygen enters your lungs, it starts filling the small sacs in the lungs known as alveoli. There are tiny blood vessels known as capillaries that surround the alveoli, and under normal circumstances, oxygen diffuses from the alveoli into the bloodstream through the capillaries.

Shunt

In this type of hypoxemia, the blood enters into the left side of your heart without getting oxygenated in the lungs.

Typically what happens is the deoxygenated blood enters into the right side of your heart, traveling to the lungs to get more oxygen, and then traveling back to the left side of the heart to get distributed throughout the body. So when the blood enters the left side of the heart, it is unable to get sufficient oxygen needed to get distributed throughout the body.

Low Environmental Oxygen

This kind of hypoxemia is known to occur at places in higher altitudes. The available amount of oxygen present in the air is known to go down as the altitude increases.
Therefore, when you are at higher altitudes, taking each breath provides you with a lower level of oxygen.

Hypoventilation

Hypoventilation is a condition when your oxygen intake happens at a slower rate. This causes an increase in the levels of carbon dioxide in the blood, along with lower levels of oxygen.

What are the Causes of Hypoxemia?

There are many different causes of hypoxemia. These can include:

  • Asthma
  • Anemia
  • Acute Respiratory Distress Syndrome (ARDS)
  • Collapsed lung
  • Blood cut in the lung (a condition known as pulmonary embolism)
  • Chronic Obstructive Pulmonary Disease (COPD)
  • Congenital heart disease or defects
  • Presence of fluid in the lung (a condition known as pulmonary edema)
  • Interstitial lung disease
  • High altitudes
  • Pneumonia
  • Sleep apnea
  • Scarring of the lungs (a condition known as pulmonary fibrosis)

Medications that reduce the breathing rate, including anesthetics and some narcotics

These different conditions also cause hypoxemia in different ways. Consider the following examples:

Anemia can cause hypoxemia. Anemia leads to a lack of sufficient red blood cells in the body in order to effectively carry oxygen throughout the body. Due to this, a person who has anemia might end up having low levels of oxygen in their blood.

A person who is suffering from COPD is also known to experience an obstruction of the flow of air in the lungs. Destruction of the walls of the alveoli in the lungs as well as the surrounding capillaries in COPD can cause problems with the process of oxygen exchange, leading to hypoxemia.(2)

Hypoxemia can also be a symptom of another underlying medical condition, including respiratory failure. Respiratory failure can take place when there is not enough oxygen present to pass from your lungs to the bloodstream. Low levels of oxygen in the blood can be a symptom of respiratory failure.

Hypoxemia can also occur in newborns who have congenital heart disease or heart defects. In fact, it is common practice to measure the oxygen levels in the blood to screen newborns for congenital heart disease or defects.(3)

Preterm infants are highly susceptible to hypoxemia, especially if they are placed on a mechanical ventilator.

What are the Symptoms of Hypoxemia?

If you have hypoxemia, you might experience the following symptoms:

How is Hypoxemia Diagnosed?

Your doctor is going to diagnose hypoxemia by first performing a physical exam to check your lungs and your heart. They may also check the color of your fingernails, skin, or your lips. Apart from this, there are also some further tests that will be performed for assessing your breathing and oxygen levels. These tests can include:

  • Breathing Tests for evaluating your breathing by breathing into a tube or checking it through a machine.
  • Pulse oximetry test that places a sensor on your finger to measure the levels of blood oxygen.
  • Arterial blood gas test that draws a blood sample from an artery to determine the levels of blood oxygen.

Is There A Treatment For Hypoxemia?

  • Yes, hypoxemia is a treatable condition. Due to the low blood oxygen levels, the treatment for hypoxemia focuses on trying to increase the levels of blood oxygen back to normal again.
  • Oxygen therapy is one treatment option that is used. This involves the use of an oxygen mask or having a small tube clipped to your nose that helps you receive supplemental oxygen.
  • If hypoxemia is being caused by another underlying medical condition such as pneumonia or asthma, then your doctor will first try to treat that condition in order to alleviate the symptoms of hypoxemia.

Complications of Hypoxemia

Everybody knows that your organs and tissues need oxygen to work properly. Due to the absence of oxygen, damage can occur to your vital organs such as the brain and the heart. Hypoxemia can prove to be fatal is it is not treated in a timely manner.

Conclusion

If you start experiencing shortness of breath all of a sudden, then you need to seek medical assistance immediately as it might impact your ability to function. In some cases, shortness of breath as a standalone symptom might not warrant a visit to the doctor, but if you experience any of the following symptoms, then you should definitely consider going to the doctor for further testing to find the underlying cause of your symptoms:

  • Shortness of breath experienced with just minimal activity or even when you are at rest
  • Shortness of breath caused by exercise and getting progressively worse
  • Waking up suddenly from sleep feeling short of breath

Hypoxemia is a condition that involves low levels of blood oxygen. It is a serious condition and can cause organ damage and can even prove to be fatal if you do not get treatment. Always seek urgent medical attention if you start to feel short of breath suddenly, and it starts affecting your ability to function or think.

References:  

  1. Samuel, J. and Franklin, C., 2008. Hypoxemia and hypoxia. In Common Surgical Diseases (pp. 391-394). Springer, New York, NY.
  2. Kent, B.D., Mitchell, P.D. and McNicholas, W.T., 2011. Hypoxemia in patients with COPD: cause, effects, and disease progression. International journal of chronic obstructive pulmonary disease, 6, p.199.
  3. Centers for Disease Control and Prevention. (2019). Congenital Heart Defects Information for Healthcare Providers | CDC. [online] Available at: https://www.cdc.gov/ncbddd/heartdefects/hcp.html [Accessed 27 Jun. 2019].

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