Oxygen saturation

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Template:WikiDoc Cardiology News Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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 such as an oxygen sensor or an optode in liquid media, usually water.

Medical science

In medicine, oxygen saturation (S_O2) 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 oxygen-haemoglobin dissociation 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 Sa_O2 (arterial oxygen saturation) value below 90% is termed hypoxemia. This may be due to various medical conditions.

The Sv_O2 (venous oxygen saturation) is measured to see how much oxygen the body consumes. Under clinical treatment, a Sv_O2 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.

Tissue oxygen saturation (St_O2) can be measured by near infrared spectroscopy. Although the measurements are still widely discussed, they give an idea of tissue oxygenation in various conditions.

Saturation of Peripheral Oxygen (Sp_O2) is an estimation of the oxygen saturation level usually measured with a pulse oximeter device.

Environmental sciences

Annual mean sea surface dissolved oxygen for the World Ocean. Data from the World Ocean Atlas 2001.

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.

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Tables such as these of DO in milliliters per liter (ml/L) are based upon empirical equations that have been worked out and tested (e.g.,Weiss, 1970):

  <math>ln(DO) = A1 + A2*100/T + A3*ln(T/100) + A4*T/100 + S*[B1 + B2*T/100 + B3*(T/100)^2]</math>

  <math>A1 = -173.4292</math>
  <math>A2 = 249.6339</math>
  <math>A3 = 143.3483</math>
  <math>A4 = -21.8492</math>
  <math>B1 = -0.033096</math>
  <math>B2 = 0.014259</math>
  <math>B3 = -0.001700</math>

T = temperature in kelvins, and S = salinity in g/kg. DO = dissolved oxygen in ml/L. ln is the natural log. Multiply DO by 1.4276 to obtain mg/L.

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Supersaturation can sometimes be harmful for organisms and cause gas bubble disease.
DO - at least 4 - 6 mg/L (ppm), but more is better

References

• Weiss, R. (1970) Deep-Sea Res. 17, 721-735
• Interactive haemoglobin saturation graph

See also

• Wastewater quality indicators discusses both Biochemical oxygen demand (BOD) and Chemical oxygen demand (COD) as indicators of wastewater quality.

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