title: Clinical probability and alveolar dead space measurement for suspected pulmonary embolism in patients with an abnormal D-dimer test result.
abstract: BACKGROUND
  Most patients with suspected pulmonary embolism (PE) have a positive D-dimer test and undergo diagnostic imaging. Additional non-invasive bedside tests are required to reduce the need for further diagnostic tests.
  
  
  OBJECTIVE
  We aimed to determine whether a combination of clinical probability assessment and alveolar dead space fraction measurement can confirm or exclude PE in patients with an abnormal D-dimer test.
  
  
  METHODS
  We assessed clinical probability of PE and alveolar dead space fraction in 270 consecutive in- and outpatients with suspected PE and positive D-dimer. An alveolar dead space fraction < 0.15 was considered normal. PE was subsequently excluded or confirmed by venous compression ultrasonography, spiral computed tomography and a 3-month follow-up. Radiologists were unaware of the results of clinical probability and capnography.
  
  
  RESULTS
  PE was confirmed in 108 patients (40%). Capnography had a sensitivity of 68.5% (95% confidence interval [CI]: 58.9-77.1%) and a specificity of 81.5% (95% CI: 74.6-87.1%) for PE. Forty-five patients (16.6%) had both a low clinical probability and normal capnography (sensitivity: 99.1%, 95% CI: 94.9-100%) and 34 patients (12.6%) had both a high clinical probability and abnormal capnography (specificity: 100%, 95% CI: 97.7-100%).
  
  
  CONCLUSIONS
  Capnography alone does not exclude PE accurately. The combination of clinical probability and capnography accurately excludes or confirms PE and avoids further testing in up to 30% of patients.
authors.affiliation: Service de Pneumologie et Soins Intensifs, Université Paris V René Descartes, Faculté de Médecine, Assistance Publique Hôpitaux de Paris, Hôpital Européen Georges Pompidou, Paris, France.
authors.forename: O
authors.initials: O
authors.lastname: Sanchez
authors.forename: D
authors.initials: D
authors.lastname: Wermert
authors.forename: C
authors.initials: C
authors.lastname: Faisy
authors.forename: M-P
authors.initials: MP
authors.lastname: Revel
authors.forename: J-L
authors.initials: JL
authors.lastname: Diehl
authors.forename: H
authors.initials: H
authors.lastname: Sors
authors.forename: G
authors.initials: G
authors.lastname: Meyer
mesh_terms: D019296:Capnography / Q000592:standards; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis*; D006801:Humans; D011336:Probability; D011650:Pulmonary Alveoli / Q000000981:diagnostic imaging / Q000473:pathology*; D011655:Pulmonary Embolism / Q000175:diagnosis* / Q000000981:diagnostic imaging; D012680:Sensitivity and Specificity; D036542:Tomography, Spiral Computed; D014463:Ultrasonography
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D