Oxygen saturation is a relative measure of the amount of oxygen that is dissolved or carried in a given medium. It can be measured with a dissolved oxygen probe in liquid media, usually water.

Medical science

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In medicine, oxygen saturation (SaO₂) measures the percentage of 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 S curve and approaches 100% at partial oxygen pressures of >10 kPa. A pulse oximeter relies on the light absorption characteristics of saturated hemoglobin to give an indication of oxygen saturation.

An SaO₂ (arterial oxygen saturation) value below 90% is termed hypoxemia. This may be due to various medical conditions.

The SvO₂ is measured to see how much oxygen the body consumes. Under clinical threatment, a SvO₂ below 60%, 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 (Extra Corporal Circulation), and can give the perfusionist an idea of how much flow the patient needs to stay healthy.

Environmental sciences

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In aquatic environments, oxygen saturation is a relative measure of the amount of oxygen (O₂) dissolved in the water. Dissolved oxygen (DO) is measured in standard solution units such as millimoles O₂ per liter (mmol/L), milligrams O₂

• 20 °C, normal pressure, freshwater: 9.1 mg/L = 100% saturation

Solubility tables (based upon temperature) and corrections for different salinities and pressures can be found at the USGS web site. Tables such as these of DO in milliliters per liter (ml/L) are based upon equations that have been worked out and tested $B\_3\; =\; -0.001700$, T = temperature in kelvins, and S = salinity in g/kg. DO = dissolved oxygen in ml/L. Multiply DO by 1.4276 to obtain mg/L.

Supersaturation can sometimes be harmful for organisms and cause gas bubble disease.

Reference

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• Weiss. 1970. Deep-Sea Res., 17:721-735

See also

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• Wastewater quality indicators discusses both BOD and COD as indicators of wastewater quality.

Blood | Ecology

Iltmætning | Sauerstoffsättigung | 溶存酸素量