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Chest. 2004 Mar;125(3):841-50.

Volumetric capnography as a screening test for pulmonary embolism in the emergency department.

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Department of Emergency and Intensive Care, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, Bruxelles, Belgium.



To compare the diagnostic performance of volumetric capnography (VCap), which is the plot of the expired CO(2) partial pressure against the expired volume during a single breath, with the PaCO(2) to end-tidal CO(2) (EtCO(2)) gradient, in the case of suspected pulmonary embolism (PE).


Single-center, prospective study.


Emergency department of a teaching hospital.


A total of 45 outpatients with positive enzyme-linked immunosorbent assay d-dimer levels of > 500 ng/mL. The diagnosis of PE was confirmed in 18 outpatients according to a validated procedure based on the ventilation-perfusion lung scan and/or spiral CT scanning.


Curves of VCap were obtained from a compact monitor connected to a computer. A sequence of four to six stable breaths allowed the calculation of the following several variables: alveolar dead space fraction; the ratio of alveolar dead space (VDalv) to airway dead space (VDaw); the VDalv to physiologic dead space (VDphys) fraction; the slope of phase 3; and the late dead space fraction (Fdlate) corresponding to the extrapolation of the capnographic curve to a volume of 15% of the predicted total lung capacity.


The mean (+/- SD) PaCO(2)-EtCO(2) gradient was 5.3 +/- 0.7 mm Hg in the PE-positive group and 2.8 +/- 0.7 mm Hg in the PE-negative group (p = 0.019). Four variables of the VCap exhibited a statistical difference between both groups, as follows: the VDalv/VDaw fraction(;) the slope of phase 3; the VDalv/VDphys fraction; and the Fdlate, which was 8.2 +/- 3.3% vs -7.7 +/- 2.8%, respectively (p = 0.000011). The diagnostic performance expressed as the mean area under a receiver operating characteristic curve comparison was 75.9 +/- 7.4% for the PaCO(2)-EtCO(2) gradient and 87.6 +/- 4.9% for the Fdlate (p = 0.02).


Fdlate, a variable of VCap, had a statistically better diagnostic performance in suspected PE than the PaCO(2)-EtCO(2) gradient. VCap is a promising computer-assisted bedside application of pulmonary pathophysiology. Future research should define the place of this technique in the diagnostic workup of PE, especially in the presence of positive d-dimers.

[Indexed for MEDLINE]

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