Oxygen saturation

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Oxygen binding curve

The oxygen saturation ( sO 2 ) indicates what percentage of the total hemoglobin in the blood is loaded with oxygen . Among other things, it allows statements to be made about the effectiveness of oxygen transport, i.e. primarily about breathing . The oxygen saturation can be determined either directly in a blood sample by a blood gas analysis or non-invasively by means of pulse oximetry . The photometric method of oximetry is based on two methods.

Oxygen saturation and oxygen partial pressure

The higher the oxygen partial pressure ( pO 2 ) in the blood , the higher the oxygen saturation . Because the oxygen affinity of the hemoglobin is dependent on the number of O 2 molecules already bound ( cooperativity ), this relationship is non-linear. The oxygen binding curve shows an inclined S-shaped course.

Standard values:

Standard values
pO 2 sO 2
arterial: 71-100 mm Hg 94-97%
mixed venous: 36-44 mm Hg 65-82%

Areas of application and relevance

Common abbreviations for oxygen saturations of various origins
sO 2 Oxygen saturation in general
S a O 2 arterial oxygen saturation (measurement in arterial blood sample)
S p O 2 Oxygen saturation measured by pulse oximetry (quasi-arterial)
S v O 2 venous oxygen saturation
S zv O 2 central venous oxygen saturation
S O 2 mixed venous oxygen saturation

The arterial oxygen saturation ( S a O 2 ) is an important, detectable by blood gas analysis Parameter for the evaluation of the respiratory function. In many cases it allows conclusions to be drawn about the function and activity of the lungs . Depending on the clinical picture, age and situation of the patient, different saturation values ​​can or must be tolerated. With children and young adults, under normal circumstances, a value close to 100% will be aimed for, with older people or certain diseases ( e.g. COPD or cystic fibrosis ) values ​​around 90% can also be sufficient: The limit for tolerable saturation must, however, be set individually: In professional mountaineers, for example, surprisingly low oxygen saturation values ​​can be detected on high peaks (<70%); these values ​​would be highly critical for most people under normal circumstances. There is therefore the assumption that not only the oxygen saturation is important, but also the individual efficiency in using oxygen. The decisive peripheral oxygen saturation is required to calculate the arterial oxygen content (C a O 2 ), which is becoming ever more clinically important, with the help of the hemoglobin content and the Hüfner number . It is important here that a high hemoglobin content can represent a compensation mechanism for a reduced saturation.

In addition to the determination in the arterial blood, the oxygen saturation is also examined in the venous blood (S v O 2 ) of various flow areas. The oxygen uptake of the tissue can be estimated from the difference to arterial saturation (S a O 2 ), taking into account the blood flow . On the other hand, assuming constant oxygen uptake, an increase in the difference indicates a decrease in blood flow. Depending on the origin of the blood sample , information about the state of the O 2 supply in the upstream organs can be obtained. For scientific investigations and special questions, the local organ blood flow can be determined according to the same principle ( hepatic vein , neck vein , coronary sinus, etc.).

See also

Web links

  • Oxygen saturation (SO 2 ) A simulation of the parameters CO 2 , pH and temperature on the oxygen binding curve (right and left shift).

Individual evidence

  1. Burchardi, Larsen, Schuster; "Die Intensivmedizin", p. 104; Springer 2003 9th edition; ISBN 3-540-00882-9
  2. Guder, Notte; "Das Laborbuch", p. 999; Elsevier 2009, 2nd edition; ISBN 978-3-437-23341-8
  3. BBC "To Boldly Go", GB, 2012, German first broadcast "Body at the Limit" on February 9, 2013 Spiegel TV Wissen