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The Physiologic Dead Space (Bohr Method) calculator computes the volume of dead space (VD) based on the tidal volume (VT) and the partial pressures of carbon dioxide in arterial blood, exhaled air and ambient air.
INSTRUCTIONS: Choose units and enter the following:
- (VT) This is the tidal volume
- (PaCO2) This is the partial pressure of carbon dioxide in arterial blood
- (PeCO2) This is the partial pressure of carbon dioxide in exhaled air
Volume of Dead Space (VD): The calculator returns the volume in liters. However, this can be automatically converted to compatible units via the pull-down menu.
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The Math / Science
The physiological dead space is the sum of the anatomical and alveolar dead spaces, and represents all components of the tidal volume that do not take part in gas exchange.Dead space is that part of inspired air that is exhaled without the benefit of exposure to perfused alveoli.Bohr’s method measures the volume of the lung that does not eliminate CO2. Because this is a functional measurement.
The carbon dioxide content of mixed exhaled gas (PECO2) is determined by the carbon dioxide content of the gas that came in contact with perfused alveoli (PACO2), the content of the gas that did not come in contact with perfused alveoli, and the proportion of the two. The Borh Method formula to compute the Physiologic Dead Space is:
`V_D = V_t * ((P_a CO_2 - P_e CO_2)/(P_a CO_2))`
where:
- VD = physiologic dead space (Bohr Method)
- VT = tidal volume
- PaCO2 = partial arterial pressure of CO2
- PECO2 = partial expired pressure of CO2
