Validation of Bohr dead space measured by volumetric capnography

Abstract

VD(Bohr) can be calculated with accuracy using volumetric capnography.

Comment on Tusman et al.: Validation of Bohr dead space measured by volumetric capnography

“…The same is true in Fig. 1, and in the results section where VD Bohr is said to be expressed in milliliters although it really corresponds to a ratio [1]. These small oversights may confuse the reader.…”

“…Their analysis based on an equation fitting the CO 2 expirogram provides a substantial improvement for the objective assessment of its components [1].…”

“…Even though it is clear that the use of PaCO 2 as a surrogate for ideal alveolar PCO 2 in the Bohr equationas suggested by Enghoff-may lead to overestimation of physiological dead space [2,3], replacing it for mean alveolar PCO 2 (PACO 2 )-as originally devised by Bohr and recently accomplished by Tusman et al [1]-will solely account for airway dead space (VD aw ) and not for alveolar dead space (VD alv ). This is shown by the following set of equations.…”

“…According to the alveolar gas equation, the mean alveolar CO 2 fraction (FACO 2 ) is the ratio between VCO 2 br and VT alv , or FACO 2 = VCO 2 br/(VT-VD aw ). Replacing the terms above in the Bohr equation as suggested by Tusman et al [1] gives:…”

“…In the introduction of Tusman's paper [1], VD Bohr , instead of VD Bohr / VT, is presented as equal to (PACO 2 -PeCO 2 )/PACO 2 . The same is true in Fig.…”