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What Are Blood Oxygen Levels? Chart, Normal, Low & High

Blood oxygen levels can also be measured using an instrument known as a pulse oximeter.

Blood oxygen levels (arterial oxygen) indicate the oxygen levels present in the blood that flows through the arteries of the body. 

An ABG test uses blood drawn from an artery, where the oxygen and carbon dioxide levels can be measured before they enter body tissues.  The blood will be put in an ABG machine (blood gas analyzer) that provides your blood oxygen levels in the form of the partial pressure of oxygen (PaO2).

  • Hyperoxemia is generally detected using ABG testing and is defined as blood oxygen levels above 120 mmHg.
  • Normal arterial oxygen pressure (PaO2) measured using the arterial blood gas (ABG) test is approximately 75 to 100 millimeters of mercury (75-100 mmHg).
  • When the level goes below 75 mmHg, the condition is generally termed hypoxemia.
  • Levels under 60 mmHg are considered very low and indicate the need for supplemental oxygen. Supplemental oxygen is provided through an oxygen cylinder that is connected to the nose via a tube, with or without a mask.

What should oxygen levels be?

Blood oxygen levels can also be measured using an instrument known as a pulse oximeter.

  • The normal oxygen levels in a pulse oximeter usually range from 95% to 100%.
  • Blood oxygen levels below 90% are considered low (hypoxemia).

Hyperoxemia is generally detected using ABG testing and is defined as blood oxygen levels above 120 mmHg. This is mostly seen in hospitals when patients are exposed to high pressures of supplemental oxygen for prolonged periods (3 to more than 10 hours).

Asthma and Low Blood Oxygen Level

What are asthma symptoms and signs?

Many of the symptoms and signs of asthma are nonspecific and can be seen in other conditions as well. Symptoms that might suggest conditions other than asthma include new symptom onset in older age, the presence of associated symptoms (such as chest discomfort, lightheadedness, palpitations, and fatigue), and lack of response to appropriate medications for asthma.

The physical exam in asthma is often completely normal. Occasionally, wheezing is present. In an asthma exacerbation, the respiratory rate increases, the heart rate increases, and the work of respiration increases. Individuals often require accessory muscles to breathe, and breath sounds can be diminished. It is important to note that the blood oxygen level typically remains fairly normal even in the midst of a significant asthma exacerbation. Low blood oxygen level is therefore concerning for impending respiratory failure.

What causes blood oxygen levels to become low?

Blood oxygen levels can get low due to any of the problems that include:

  • Low air oxygen levels: Atmospheric oxygen becomes extremely low at high altitudes such as mountainous regions.
  • Decreased capacity of the body to take in oxygen:
    • This can be caused by lung conditions that include:
      • Asthma
      • Emphysema (damage of the air sacs in the lung)
      • Bronchitis
      • Pneumonia
      • Pneumothorax (leaking of air in the space between the lung and chest wall)
      • Acute respiratory distress syndrome (ARDS)
      • Pulmonary edema (the lung swells due to build-up of fluid)
      • Pulmonary fibrosis (scarring of the lungs)
      • Interstitial lung disease (a large group of lung disorders that generally cause progressive scarring of the lungs)
      • Viral infections such as COVID-19
  • Other conditions include:
    • Anemia
    • Sleep apnea (temporary cessation of breathing during sleep)
    • Smoking
  • Decreased capacity of the heart to supply the oxygenated blood back to the lungs: The most common causes are congenital heart diseases (heart defects present by birth).

SLIDESHOW

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How are blood oxygen levels checked using the ABG test?

  • Blood oxygen levels can be checked by withdrawing blood from your artery present in the wrist, elbow, or groin.
  • You may feel a sharp pain when the needle enters the artery.
  • The blood will be put in an ABG machine (blood gas analyzer) that provides your blood oxygen levels in the form of the partial pressure of oxygen (PaO2).

How are blood oxygen levels checked using a pulse oximeter?

A pulse oximeter is a small, mobile, and handy medical device.

  • It is most commonly used when doctors want to know your blood oxygen levels quickly.
  • It is also used to monitor the response of your body to certain medications or supplemental oxygen.
  • Blood oxygen levels are indicated as SpO2, which is the percent saturation of oxygen in the blood.

The test that measures blood oxygen levels using a pulse oximeter is known as pulse oximetry. The procedure is very simple and requires only clipping the pulse oximeter in between any of the fingers for a few seconds. The reading appears on the pulse oximeter screen. This test may be slightly less accurate than ABG but is easier to perform than ABG tests when needed quickly.

  • The brain gets affected when the SpO2 level falls below 80-85%.
  • Cyanosis develops when the SpO2 level drops below 67%.
  • The normal oxygen levels in a pulse oximeter usually range from 95% to 100%.  Note: Normal levels may vary if you have lung disorders. Your doctor can tell what levels are normal for you.

Blood Oxygen Levels Chart Using a Pulse Oximetry

Condition
SpO2 Range

Normal
95% to 100%

Brain Gets Affected
80% to 85%

Cyanosis
Below 67%

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What are the signs and symptoms of hypoxemia?

Hypoxemia can give rise to many signs and symptoms depending on its severity, which may include:

  • Headache (mild to severe)
  • Shortness of breath
  • Dizziness
  • Coughing
  • Wheezing (breathing with a whistling or rattling sound in the chest)
  • Confusion
  • Rapid heartbeat
  • Cyanosis (bluish color in the skin, fingernails, and lips)

Not having enough blood oxygen levels results in inadequate oxygen supply to the organs and tissues of the body. Severe hypoxemia can become dangerous. If left untreated for a long time, it can end up affecting the brain or heart.

How is hypoxemia treated?

Treating hypoxemia involves measures that increase the levels of oxygen in the blood, which is achieved by:

  • Treating underlying conditions: Treating the cause of hypoxemia is the most important part of the therapy that gives long-lasting effects. Many times, medications are given through an inhaler that quickly enables you to breathe the medicine into your lungs.
  • Oxygen therapy: You are given supplemental oxygen through an oxygen cylinder (which can be portable). The pressure of delivered oxygen can be controlled.

How can you prevent hypoxemia?

You can maintain your normal blood oxygen levels after you recover from hypoxemia.

Here are a few lifestyle steps you can take to help prevent hypoxemia:

  • Deep breathing exercises
  • Mild exercise such as walking or as advised by your doctor
  • Yoga
  • Eat a healthy, well-balanced diet
  • Drink water adequately
  • Quit smoking

QUESTION

COPD (chronic obstructive pulmonary disease) is the same as adult-onset asthma.
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Medically Reviewed on 2/25/2022

References

Hypoxemia. Available at: https://www.mayoclinic.org/symptoms/hypoxemia/basics/definition/sym-20050930

Hafen BB, et al. Oxygen Saturation. In: StatPearls [Internet]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK525974/

Cooper JS, et al. Oxygen Toxicity. In: StatPearls [Internet]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK430743/

Starr N, et al. Pulse oximetry in low-resource settings during the COVID-19 pandemic. The Lancet Global Health. 2020 Sep 1;8(9):e1121-2.

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