Oxygen Content (O
2
Ct)
Oxygen content is dened as the total amount of oxygen
contained in a given volume of whole blood, including
dissolved oxygen and oxygen bound to hemoglobin. It is
expressed in milliliters of oxygen per 100 milliliters of blood
(volume %) as calculated from the oxygen saturation and the
hemoglobin concentration. Four moles of oxygen (22,393
mL/mol at standard temperature and pressure) can combine
with 1 mole of hemoglobin (64,458 g/mol) so that oxygen
capacity is equal to
4 (22393)
_________
= 1.39 mL of O
2
per gram of Hb Equation 23
64458
therefore O
2
Ct = (1.39 [Hb]) (SO
2
/100) + (0.0031 [PO
2
])
Equation 24
where 0.0031 is the solubility coefcient of O
2
.
On the analyzer, hemoglobin can be manually entered,
calculated from the measured hematocrit, or occur as a
default value.
Oxygen Saturation (O
2
Sat)
Oxygen saturation is dened as the amount of oxyhemoglobin
in blood expressed as a fraction of the total amount of
hemoglobin able to bind oxygen. It is calculated as follows:
[PO
2
']
3
+ 150 [PO
2
']
O
2
Sat = –––––––––––––––––––––––– x100 Equation 25
[PO
2
']
3
+ 150 [PO
2
'] + 23400
where [PO
2
'] = [PO
2
] x e [2.3026 x (0.48 (pH – 7.4) –
0.0013([HCO
3
-
] – 25))]
NOTE: The equation for calculating oxygen saturation
assumes a normal shape and position of the
patient's oxygen dissociation curve.
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