title: Steady-state end-tidal alveolar dead space fraction and D-dimer: bedside tests to exclude pulmonary embolism.
abstract: OBJECTIVE
  Less than 35% of patients suspected of having pulmonary embolism (PE) actually have PE. Safe bedside methods to exclude PE could save health-care resources and improve access to diagnostic testing for suspected PE. In patients with suspected PE, we sought to determine the sensitivity, specificity, and negative predictive value of (1) a steady-state end-tidal alveolar dead space fraction (AVDSf) of < 0.15, (2) a negative D-dimer result, and (3) the combination of a steady-state end-tidal AVDSf of < 0.15 and a negative D-dimer result.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  Tertiary-care center in Ottawa, Ontario, Canada.
  
  
  METHODS
  Consecutive inpatients, outpatients, and emergency department patients with suspected PE referred to the Departments of Nuclear Medicine or Radiology for investigation of suspected PE.
  
  
  METHODS
  All study patients had D-Dimer and alveolar dead space measurements prior to determining outcome (PE or no PE) with ventilation/perfusion scans and/or noninvasive leg vein imaging and/or pulmonary angiography.
  
  
  RESULTS
  Two hundred forty-six eligible and consenting patients underwent diagnostic imaging that excluded PE in 163 patients, diagnosed PE in 49 patients, and was indeterminant in 34 patients. A negative D-dimer result excluded PE with a sensitivity of 83.0% (95% confidence interval [CI], 69.2 to 92.4%), a negative predictive value of 91.2% (95% CI, 83.4 to 96.1%), and a specificity of 57.6%. A steady-state end-tidal AVDSf of < 0.15 excluded PE with a sensitivity of 79.5% (95% CI, 63.5 to 90.7%), a negative predictive value of 90.7% (95% CI, 82.5 to 95.9%), and a specificity of 70.3%. The combination of a negative D-dimer result and a steady-state end-tidal AVDSf of < 0.15 excluded PE with a sensitivity of 97.8% (95% CI, 88.5 to 99.9%), a negative predictive value of 98.0% (95% CI, 89.4 to 99.9%), and a specificity of 38.0%.
  
  
  CONCLUSIONS
  This simple combination of bedside tests may safely rule out PE without further diagnostic testing in large numbers of patients with suspected PE.
authors.affiliation: Department of Medicine, University of Ottawa, Ontario, Canada. mrodger@ottawahospital.on.ca
authors.forename: M A
authors.initials: MA
authors.lastname: Rodger
authors.forename: G
authors.initials: G
authors.lastname: Jones
authors.forename: P
authors.initials: P
authors.lastname: Rasuli
authors.forename: F
authors.initials: F
authors.lastname: Raymond
authors.forename: H
authors.initials: H
authors.lastname: Djunaedi
authors.forename: C N
authors.initials: CN
authors.lastname: Bredeson
authors.forename: P S
authors.initials: PS
authors.lastname: Wells
mesh_terms: D003937:Diagnosis, Differential; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D019095:Point-of-Care Systems; D011237:Predictive Value of Tests; D011336:Probability; D011446:Prospective Studies; D011650:Pulmonary Alveoli / Q000503:physiopathology; D011655:Pulmonary Embolism / Q000175:diagnosis*; D012126:Respiratory Dead Space; D012129:Respiratory Function Tests; D012680:Sensitivity and Specificity
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D