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If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

A normal blood oxygen level depends on what exactly you’re measuring. The partial pressure of oxygen in a sample of arterial blood (PaO2) is normally 75–100 mm Hg. The partial pressure of oxygen in a sample of venous blood (PvO2) varies but is lower than this. The arterial oxygen saturation (SaO2), which can be measured by wearing a pulse oximeter, is normally >95%

One of the primary functions of the blood is to carry oxygen around the body, delivering it to the tissues. The arteries carry blood away from the heart and contain more oxygen; the veins carry blood back to the heart and contain less oxygen. Having a low blood oxygen level means less oxygen is available for use by the body’s cells, which hinders cellular energy production. This can cause shortness of breath, headache, confusion, and—if oxygen levels are very low—organ damage and death. Low blood oxygen levels typically result from lung disease.
Low blood oxygen levels are addressed by treating the underlying problem. If this isn’t possible, supplemental oxygen (breathing oxygen through a tube) may be necessary. In some circumstances, such as in individuals with chronic obstructive pulmonary disease (COPD), it may be more appropriate to keep the SaO2 between 88–92%.

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Hypoxemia occurs when levels of oxygen in the blood are lower than normal. If blood oxygen levels are too low, your body may not work properly. Blood carries oxygen to the cells throughout your body to keep them healthy. Hypoxemia can cause mild problems such as headaches and shortness of breath. All cellular blood components are derived from haematopoietic stem cells. In a healthy adult person, approximately 10 11 –10 12 new blood cells are produced daily in order to maintain steady state levels in the peripheral circulation. A healthy oxygen saturation is typically above 90%. If your number dips below 90%, Dr. Tsuang says, call your doctor for advice. Remember, too, that low oxygen is just one sign of COVID-19.

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In medicine, using the term “normal” can sometimes be off-putting. Saying something is “normal” implies that everything else is “abnormal.” Additionally, saying something is “normal” may not be accurate, since something that is “normal” for you may not be “normal” for somebody else. Therefore, instead of saying certain values are “normal,” alternative terminology may be to say that these values are “healthy” or “within the reference range.”
Additionally, some values have well-defined cutoffs, while others do not. For example, when looking at hemoglobin A1c levels, a value of 6.5 or greater is always diagnostic of diabetes. On the other hand, when looking at testosterone levels, some use cutoffs of 270–1,070 ng/dL while others use cutoffs of 300–1,000 ng/dL.
The information below represents values that are commonly used as cutoffs. However, depending on the specific source you’re looking at or the laboratory you go to, their values may be a little different.

Blood circulation: Red = oxygenated (arteries), Blue = deoxygenated (veins)

Oxygen saturation is the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal arterial blood oxygen saturation levels in humans are 95–100 percent. If the level is below 90 percent, it is considered low and called hypoxemia.[1] Arterial blood oxygen levels below 80 percent may compromise organ function, such as the brain and heart, and should be promptly addressed. Continued low oxygen levels may lead to respiratory or cardiac arrest. Oxygen therapy may be used to assist in raising blood oxygen levels. Oxygenation occurs when oxygen molecules (O
2
) enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.

What Is Healthy Blood Oxygen Levels

Definition[edit]

Hemoglobin saturation curve

In medicine, oxygen saturation, commonly referred to as 'sats', measures the percentage of hemoglobin binding sites in the bloodstream occupied by oxygen.[2] At low partial pressures of oxygen, most hemoglobin is deoxygenated. At around 90% (the value varies according to the clinical context) oxygen saturation increases according to an oxygen-hemoglobin dissociation curve and approaches 100% at partial oxygen pressures of >11 kPa. A pulse oximeter relies on the light absorption characteristics of saturated hemoglobin to give an indication of oxygen saturation.

Physiology[edit]

The body maintains a stable level of oxygen saturation for the most part by chemical processes of aerobic metabolism associated with breathing. Using the respiratory system, red blood cells, specifically the hemoglobin, gather oxygen in the lungs and distribute it to the rest of the body. The needs of the body's blood oxygen may fluctuate such as during exercise when more oxygen is required [3] or when living at higher altitudes. A blood cell is said to be 'saturated' when carrying a normal amount of oxygen.[4] Both too high and too low levels can have adverse effects on the body.[5]

Measurement[edit]

An SaO2 (arterial oxygen saturation, as determined by an arterial blood gas test[6]) value below 90% indicates hypoxemia (which can also be caused by anemia). Hypoxemia due to low SaO2 is indicated by cyanosis. Oxygen saturation can be measured in different tissues:[6]

  • Venous oxygen saturation (SvO2) is the percentage of oxygenated hemoglobin returning to the right side of the heart. It can be measured to see if oxygen delivery meets the tissues' demands. SvO2 typically varies between 60% and 80%.[7] A lower value indicates that the body is in lack of oxygen, and ischemic diseases occur. This measurement is often used under treatment with a heart lung machine (extracorporeal circulation), and can give the perfusionist an idea of how much flow the patient needs to stay healthy.
  • Tissue oxygen saturation (StO2) can be measured by near infrared spectroscopy. Although the measurements are still widely discussed, they give an idea of tissue oxygenation in various conditions.
  • Peripheral oxygen saturation (SpO2) is an estimation of the oxygen saturation level usually measured with a pulse oximeter device. It can be calculated with pulse oximetry according to the formula[6] where HbO2 is oxygenated hemoglobin (oxyhemoglobin) and Hb is deoxygenated hemoglobin.

Healthy Blood Oxygen Level Apple Watch

Pulse oximetry[edit]

Example pulse oximeter

Pulse oximetry is a method used to estimate the percentage of oxygen bound to hemoglobin in the blood.[8] This approximation to SaO2 is designated SpO2 (peripheral oxygen saturation). The pulse oximeter consists of a small device that clips to the body (typically a finger, an earlobe or an infant's foot) and transfers its readings to a reading meter by wire or wirelessly. The device uses light-emitting diodes of different colours in conjunction with a light-sensitive sensor to measure the absorption of red and infrared light in the extremity. The difference in absorption between oxygenated and deoxygenated hemoglobin makes the calculation possible.[6]

Medical significance[edit]

Healthy individuals at sea level usually exhibit oxygen saturation values between 96% and 99%, and should be above 94%. At 1,600 meters' altitude (about one mile high) oxygen saturation should be above 92%.[9]

An SaO2 (arterial oxygen saturation) value below 90% causes hypoxia (which can also be caused by anemia). Hypoxia due to low SaO2 is indicated by cyanosis, but oxygen saturation does not directly reflect tissue oxygenation. The affinity of hemoglobin to oxygen may impair or enhance oxygen release at the tissue level. Oxygen is more readily released to the tissues (i.e., hemoglobin has a lower affinity for oxygen) when pH is decreased, body temperature is increased, arterial partial pressure of carbon dioxide (PaCO2) is increased, and 2,3-DPG levels (a byproduct of glucose metabolism also found in stored blood products) are increased. When the hemoglobin has greater affinity for oxygen, less is available to the tissues. Conditions such as increased pH, decreased temperature, decreased PaCO2, and decreased 2,3-DPG will increase oxygen binding to the hemoglobin and limit its release to the tissue.[10]

See also[edit]

References[edit]

  1. ^'Hypoxemia (low blood oxygen)'. Mayo Clinic. mayoclinic.com. Retrieved 6 June 2013.
  2. ^Kenneth D. McClatchey (2002). Clinical Laboratory Medicine. Philadelphia: Lippincott Williams & Wilkins. p. 370. ISBN9780683307511.
  3. ^'Understanding Blood Oxygen Levels at Rest'. fitday.com. fitday.com. Retrieved 6 June 2013.
  4. ^Ellison, Bronwyn. 'NORMAL RANGE OF BLOOD OXYGEN LEVEL'. Livestrong.com. Livestrong.com. Retrieved 6 June 2013.
  5. ^'Hypoxia and Hypoxemia: Symptoms, Treatment, Causes'. WebMD. Retrieved 2019-03-11.
  6. ^ abcd'Understanding Pulse Oximetry: SpO2 Concepts'. Philips Medical Systems. Retrieved 19 August 2016.
  7. ^https://www.lhsc.on.ca/critical-care-trauma-centre/central-venous/mixed-venous-oxygen-saturation
  8. ^Peláez EA, Villegas ER (2007). 'LED power reduction trade-offs for ambulatory pulse oximetry'. Conf Proc IEEE Eng Med Biol Soc. 2007: 2296–9. doi:10.1109/IEMBS.2007.4352784. ISBN978-1-4244-0787-3. PMID18002450. S2CID34626885.
  9. ^'Normal oxygen level'. National Jewish Health. MedHelp. February 23, 2009. Retrieved 2014-01-28.
  10. ^Schutz (2001). 'Oxygen Saturation Monitoring by Pulse Oximetry'(PDF). American Association of Critical Care Nurses. Archived from the original(PDF) on January 31, 2012. Retrieved September 10, 2011.

External links[edit]

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