Apply the Bohr equation to find VD/VT when PaCO2 is 40 mmHg and PeCO2 is 30 mmHg.

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Apply the Bohr equation to find VD/VT when PaCO2 is 40 mmHg and PeCO2 is 30 mmHg.

Bohr equation connects how much of each breath does not participate in gas exchange (dead space) to CO2 levels. The dead-space fraction of tidal volume is VD/VT = (PACO2 − PECO2) / PACO2. In many clinical problems PACO2 is approximated by PaCO2, and PECO2 is the end-tidal CO2 in expired air. Plugging in the values: (40 mmHg − 30 mmHg) / 40 mmHg = 10 / 40 = 0.25. This means 25% of the tidal volume is dead space ventilation. In other words, a quarter of each breath does not reach the gas-exchanging units.

Bohr equation connects how much of each breath does not participate in gas exchange (dead space) to CO2 levels. The dead-space fraction of tidal volume is VD/VT = (PACO2 − PECO2) / PACO2. In many clinical problems PACO2 is approximated by PaCO2, and PECO2 is the end-tidal CO2 in expired air.

Plugging in the values: (40 mmHg − 30 mmHg) / 40 mmHg = 10 / 40 = 0.25. This means 25% of the tidal volume is dead space ventilation. In other words, a quarter of each breath does not reach the gas-exchanging units.

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