Volumetric or time-based capnography for excluding pulmonary embolism in outpatients?
BACKGROUND
Volumetric capnography is technically more demanding but theoretically better than the time-based alveolar deadspace fraction (P(a)CO(2) - EtCO(2))/P(a)CO(2) as a bedside diagnostic tool for excluding pulmonary embolism (PE) in outpatients.


OBJECTIVE
We compared both diagnostic accuracy in patients with a suspected PE and positive D-dimer enzyme-linked immunosorbent assay results.


METHODS
In this clinical multicenter trial with prospective inclusion and 3-month follow-up, alveolar deadspace fraction was compared by receiver operating characteristic (ROC) analysis with other parameters derived from volumetric capnography.


RESULTS
Capnography was performed in 239 patients, and 205 tests (86%) were conclusive. The incidence of PE was 33%. The alveolar deadspace fraction accuracy expressed with ROC curve analysis was 0.73 +/- 0.04. The diagnostic performances of parameters from volumetric capnography were not significantly better. Sixteen per cent [95% confidence interval (CI) 12-21%] of patients presented a (P(a)CO(2) - EtCO(2))/P(a)CO(2) ratio under the cut-off value of 0.15, with a low clinical probability. This combination excluded PE, with a sensitivity of 96% (95% CI 89-99%) and a negative likelihood ratio of 0.17 (95% CI 0.09-0.33%).


CONCLUSIONS
Volumetric capnography failed to show superiority to alveolar deadspace fraction measurements [(P(a)CO(2) - EtCO(2))/P(a)CO(2)] for exclusion of PE in outpatients with positive D-dimer test results. Future studies should clarify the safety of excluding PE in patients combining low clinical probability with positive D-dimer results and (P(a)CO(2) - EtCO(2))/P(a)CO(2) ratios below the cut-off value of 0.15.
Verschuren
F
F
Université catholique de Louvain, Cliniques universitaires Saint-Luc, Acute Medicine Department, Accidents and Emergency Unit, Brussels, Belgium. franck.verschuren@uclouvain.be
Sanchez
O
O
Righini
M
M
Heinonen
E
E
Le Gal
G
G
Meyer
G
G
Perrier
A
A
Thys
F
F
D000368:Aged; D000369:Aged, 80 and over; D019296:Capnography; D002245:Carbon Dioxide / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D005060:Europe; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism; D006801:Humans; D016013:Likelihood Functions; D008875:Middle Aged; D010045:Outpatients; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000097:blood / Q000175:diagnosis* / Q000378:metabolism; D012372:ROC Curve; D012126:Respiratory Dead Space; D012680:Sensitivity and Specificity; D013997:Time Factors
D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D; D002245:Carbon Dioxide