Figure 1.

Graphical illustration of a volumetric capnography (VCap) curve where the partial pressure of expired CO₂ (Exp. CO₂) is plotted over the volume of one tidal breath (VT). “A” is the inflection point of VCap that separates per definition the airways from alveolar compartment and is used to calculate airway dead space (VDaw). PACO₂ is the CO₂ value at the midpoint between the inflection point “A” and the end-tidal CO₂ (P_ETCO₂). The mixed-expired CO₂ (P_E¯CO₂) represents the mean CO₂ in the expired gas. The difference between P_ETCO₂ and arterial oxygen partial pressure (PaCO₂) is plotted as well.