Oxygen saturation is the fraction of

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

-saturated

haemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobi ...

relative to total haemoglobin (unsaturated + saturated) in the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood is com ...

. 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 96–100 percent. If the level is below 90 percent, it is considered low and called

hypoxemia Hypoxemia (also spelled hypoxaemia) is an abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia is usually caused by pulmonary disease. Sometimes the concentration of oxygen in the ...

. 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 Oxygen therapy, also referred to as supplemental oxygen, is the use of oxygen as medical treatment. Supplemental oxygen can also refer to the use of oxygen enriched air at altitude. Acute indications for therapy include hypoxemia (low blood o ...

may be used to assist in raising blood oxygen levels. Oxygenation occurs when

molecules () enter the tissues of the body. For example,

is oxygenated in the

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

s, where oxygen molecules travel from the air and into the blood. Oxygenation is commonly used to refer to medical oxygen saturation.

Definition

medicine Medicine is the science and Praxis (process), practice of caring for patients, managing the Medical diagnosis, diagnosis, prognosis, Preventive medicine, prevention, therapy, treatment, Palliative care, palliation of their injury or disease, ...

, oxygen saturation, commonly referred to as "sats", measures the percentage of

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...

binding sites in the bloodstream occupied by oxygen. 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 Pulse oximetry is a noninvasive method for monitoring blood oxygen saturation. Peripheral oxygen saturation (SpO2) readings are typically within 2% accuracy (within 4% accuracy in 95% of cases) of the more accurate (and invasive) reading of art ...

relies on the light absorption characteristics of saturated hemoglobin to give an indication of oxygen saturation.

Physiology

The body maintains a stable level of oxygen saturation for the most part by chemical processes of

aerobic metabolism Cellular respiration is the process of oxidizing biological fuels using an inorganic electron acceptor, such as oxygen, to drive production of adenosine triphosphate (ATP), which stores chemical energy in a biologically accessible form. Cellu ...

associated with

breathing Breathing (spiration or ventilation) is the rhythmical process of moving air into ( inhalation) and out of ( exhalation) the lungs to facilitate gas exchange with the internal environment, mostly to flush out carbon dioxide and bring in oxy ...

. Using the

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

, red blood cells, specifically the

, 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 or when living at higher altitudes. A blood cell is said to be "saturated" when carrying a normal amount of oxygen. Both

too high ''Innervisions'' is the sixteenth studio album by American singer, songwriter, and musician Stevie Wonder, released on August 3, 1973, by Tamla, a subsidiary of Motown, Motown Records. A landmark recording of Wonder's "classic period", the albu ...

and too low levels can have adverse effects on the body.

Measurement

An SaO₂ (arterial oxygen saturation, as determined by an

arterial blood gas test An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe ...

) value below 90% indicates

(which can also be caused by

anemia Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availabl ...

). Hypoxemia due to low SaO₂ is indicated by

cyanosis Cyanosis is the change of Tissue (biology), tissue color to a bluish-purple hue, as a result of decrease in the amount of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Cyanosis is apparent usually in the Tissue (bi ...

. Oxygen saturation can be measured in different tissues:

Pulse oximetry

Pulse oximetry is a method used to estimate the percentage of oxygen bound to

in the blood. This approximation to SaO₂ is designated SpO₂ (peripheral oxygen saturation). The pulse oximeter is a small device that clips to the body (typically a finger, an earlobe or an infant's foot) and displays its reading, or transfers it to another device. Oxygenated and deoxygenated hemoglobin differ in absorption of light of different wavelengths. The oximeter uses

light-emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corre ...

s of different wavelengths in conjunction with a light-sensitive sensor to measure the absorption of red and infrared wavelengths in the extremity, and estimates the SpO₂ from the absorption spectrum.

Medical significance

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 The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a imperial unit, British imperial unit and United States customary unit of length; both are based on the older English unit of Unit of length, le ...

high) oxygen saturation should be above 92%. An SaO₂ (arterial oxygen saturation) value below 90% causes hypoxia (which can also be caused by

). Hypoxia due to low SaO₂ is indicated by

, 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.,

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.

References

External links

Interactive hemoglobin saturation graph
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