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


METHODS
Single-center, prospective study.


METHODS
Emergency department of a teaching hospital.


METHODS
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.


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Department of Emergency and Intensive Care, Cliniques Universitaires Saint-Luc, Université Catholique de Louvain, Bruxelles, Belgium. Franck.verschuren@clin.ucl.ac.be
Franck
F
Verschuren
Giuseppe
G
Liistro
René
R
Coffeng
Frédéric
F
Thys
Jean
J
Roeseler
Francis
F
Zech
Marc
M
Reynaert
D001944:Breath Tests; D019296:Capnography; D002245:Carbon Dioxide / Q000032:analysis; D004636:Emergency Service, Hospital; D004797:Enzyme-Linked Immunosorbent Assay; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis; D006801:Humans; D019095:Point-of-Care Systems; D011655:Pulmonary Embolism / Q000175:diagnosis*; D012372:ROC Curve; D012126:Respiratory Dead Space; D012680:Sensitivity and Specificity
D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D; D002245:Carbon Dioxide