There was good agreement in PeCO 2 calculated with DBag vs. PaCO 2 was higher than PACO 2, particularly in patients with ARDS (post-cardiac surgery PACO 2 = 4.3 ± 0.6 kPa vs. Subsequently, V D/V T was calculated using four methods: Enghoff-DBag, Enghoff-InCal, Enghoff-VCap, and Bohr-VCap. PeCO 2 was measured in expired air using three techniques: Douglas bag (DBag), indirect calorimetry (InCal), and VCap. PACO 2 was measured using VCap to calculate Bohr dead space or substituted with partial pressure of carbon dioxide in arterial blood (PaCO 2) to calculate the Enghoff modification. In a prospective, observational study, 15 post-cardiac surgery patients and 15 patients with ARDS were included. The purpose of the present study was to evaluate how VCap and other available techniques to measure PACO 2 and partial pressure of carbon dioxide in mixed expired air (PeCO 2) affect calculated V D/V T. Recently, a novel technique to calculate partial pressure of carbon dioxide in alveolar air (PACO 2) using volumetric capnography (VCap) was validated.

However, V D/V T is rarely calculated in clinical practice, because its measurement is perceived as challenging.

In patients with acute respiratory distress syndrome (ARDS), V D/V T has prognostic value and can be used to guide ventilator settings. Physiological dead space (V D/V T) represents the fraction of ventilation not participating in gas exchange.

Shunt vs dead space