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Overview :
The cardiac output can be
estimated by dividing oxygen consumption by the difference in oxygen content
between arterial and venous blood. The dufferebce between the arterial and
mixed venous blood oxygen concentration correlates with oxygen uptake per unit
of blood as it flows through the lungs (Fick Principle). The method is
cumbersome due to the need to collect expired air and arterial blood gases.
oxygen content in blood =
= (hemoglobin in g/dL) * (1.34 mL
oxygen per g hemoglobin) * (oxygen saturation in per cent)
where:
•
1.34 mL per g is the amount of oxygen that a gram of hemoglobin can carry if
100% saturated
•
Oxygen saturation is expressed in volume per cent (vol%), or the mL of oxygen
per 100 mL of blood.
cardiac output in liters per
minute =
= (oxygen consumption) /
((difference in oxygen content between mixed venous and arterial blood in vol%)
* 10) =
= (oxygen consumption) / (((oxygen
content arterial blood in vol%) - (oxygen content mixed venous blood in vol%))
* 10)
where:
•
Oxygen consumption can be estimated by calculating the patient's BSA and
multiplying by the basal oxygen consumption of 125 mL oxygen per square meter
BSA.
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