Test your IntelliVence (Vol 15 Issue 4)

Author: Clinical Experts Group, Hamilton Medical Group, Reviewer: Bernhard Schmitt

Why is the current volumetric capnogram loop different from the reference loop?

Answer:  Pulmonary embolism (PE). In the case of PE, there is an increase in alveolar dead space (VDalv) caused by a decrease of blood flow to alveoli that are well ventilated. This gas with low CO2 content is expired in synchrony with gas from normally perfused alveoli. This contrasts with pulmonary diseases affecting the airway, which are characterized by nonsynchronous emptying of compartments with an uneven ventilation/perfusion relationship (1).



Normal volumetric capnogram showing Phases I, II and III, and VDalv


As VDalv increases, the CO2 content of the exhaled gas therefore decreases and causes a consecutive drop in the volume of CO2 eliminated. The volumetric capnogram loop is characterized by significantly lower PetCO2* and a flatter plateau in Phase III. In addition, the slope in Phase II is less steep.




* Partial pressure of end-tidal CO2


  1. Diagnosis of Pulmonary Embolism Based upon Alveolar Dead Space Analysis. Leif Eriksson, Per Wollmer, Carl-Gustav Olsson, Ulf Albrechtsson, Hrafnhildur Larusdottir, Roma Nilsson, Anders Sjögren, Björn Jonson. Chest 1989; 96:357–6.


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Volumetric Capnography ebook
3.4 MB