Oxygen content of the blood

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The oxygen content of the blood (cO 2 ) is usually given in the unit ml / dl and then corresponds to the gas volume of oxygen in ml that is contained in 100 ml of blood.

A distinction is made between arterial (C a O 2 ) and venous oxygen content (C v O 2 ). The diagnostic significance of the arterial oxygen content is high, as it allows conclusions to be drawn about the supply of the patient with oxygen , taking into account the cardiac output .

composition

The amount of oxygen in the blood is made up of the oxygen chemically bound to the hemoglobin (Hb) and the oxygen dissolved in the blood.

The volume of oxygen bound to the hemoglobin in one deciliter of blood depends on the concentration of the hemoglobin and its oxygen saturation . The concentration of hemoglobin is given in g / dl. The oxygen saturation, ie the percentage of hemoglobin saturated with oxygen (sO 2 ), can be converted into the oxygen volume with the help of a constant, the Hüfner number . The Hüfner number indicates the maximum amount of oxygen that can be bound to the hemoglobin and is given in the literature as 1.34 ml / g (in vivo) or 1.39 ml / g (in vitro).

The volume of oxygen dissolved in the blood is calculated from the partial pressure of the oxygen (pO 2 ) and its solubility ( Henry's law ). This normally only makes up a small proportion of the total oxygen transported in the blood.

The formula for calculating the arterial oxygen content is accordingly:

C a O 2 = S a O 2 x Hb [g / dl] x 1.34 [ml / g] + p a O 2 [mmHg] x 0.0031 [1 / mmHg * ml / dl] (S a O 2 is usually given in%)

Standard values

Due to the gender-different normal values ​​of hemoglobin, the normal values ​​of the oxygen content in the arterial blood also differ in men and women: The C a O 2 in men is 20.4 ml / dl and in women 18.6 ml / dl. The venous blood usually contains 15 ml / dl. The difference between C a O 2 and C v O 2 is known as the arteriovenous oxygen content difference or arteriovenous oxygen difference (avDO 2 ) and is usually around 5 ml / dl.

If the arterial oxygen content falls below the normal values, this is called arterial hypoxemia . A drop in C a O 2 to a value below 12 ml / dl is considered critical.

Individual evidence

  1. ^ A b Heck, Fresenius: Repetitorium Anästhesiologie. Springer, Berlin; 5th edition 2007. ISBN 978-3-540-46575-1
  2. ^ Hans Walter Striebel: Anesthesia, intensive care medicine, emergency medicine. Schattauer Verlag, Stuttgart, New York; 7th edition 2009; ISBN 978-3-7945-2635-2 , p. 344
  3. ↑ Wolfgang Oczenski: Breathing and breathing aids: breathing physiology and ventilation technology. P. 89 . Thieme Verlag, Stuttgart 2008, ISBN 978-3-13-137698-5 . Online: limited preview in Google Book search
  4. ↑ H. Burchardi, R. Larsen, R. Kuhlen, K.-W. Jauch, J. Schölmerich: The intensive medicine. P. 162 . Springer Verlag, Berlin, Heidelberg 2007, ISBN 978-3-540-72295-3 . Online: limited preview in Google Book search
  5. ↑ Reinhard Larsen: Anesthesia. Urban and Schwarzenberg 1987; ISBN 3-541-11002-3 , p. 81