Arterial Blood Gases: Calculations - Deadspace to Tidal Volume Ratio (Vd/Vt)
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What is the formula to Vd/Vt?
(PaCO2-PeCO2/ PaCO2) x 100
What does the dead space to tidal volume ratio measure?
The percentage of the tidal volume that is dead space and does not participate in gas exchange (ventilation without perfusion)
If given the Vt but the Vd must be calculated, what formula should be used?
Vd/Vt x Vt
An increase/decrease in the Vd/Vt ratio indicates that a dead space producing disease is present (such as PE)?
Increase
What is the average PCO2 of the exhaled air that can be measured by a capnograph?
PeCO2
What is the normal value for (Vd/Vt)?
20 to 40% (up to 60% for ventilator patients)
