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By combining an ABG with end-tidal CO2 measurements. We can accurately predict our patient’s fraction of dead space and monitor for changes in dead space.
PaCO2-PECO2/PaCO2 = Fraction of dead space.
When your patient’s PECO2 is significantly lower than the PaCO2, think about increasing dead space.
- Dead space is gas in the pulmonary system that does not participate in gas exchange.
- We have normal anatomic dead space made up of the trachea and bronchial tree.
- Patients also have physiologic dead space composed of alveoli that are not participating in gas exchange.
- When the fraction of dead space exceeds 0.3, we must have a concern that our patient’s physiologic dead space is increasing.