title: Respiratory dead space measurement in the investigation of pulmonary embolism in outpatients with pleuritic chest pain.
abstract: OBJECTIVE
  Pleuritic chest pain is a common presenting condition in the emergency department. A noninvasive bedside rule out test for pulmonary embolism would aid investigating this patient group. Our study aimed to compare the clinical utility of three methods for calculating respiratory dead space in the diagnosis of pulmonary embolism in outpatients with pleuritic chest pain.
  
  
  METHODS
  Prospective diagnostic study.
  
  
  METHODS
  Large city-center emergency department.
  
  
  METHODS
  Between February 2002 and June 2003, 425 patients presenting to the emergency department with pleuritic chest pain were prospectively recruited.
  
  
  METHODS
  Data collection for respiratory dead space was performed in the emergency department by two researchers. The respiratory dead space fraction was calculated independently using three different methods. All patients underwent an independent reference standard diagnostic algorithm to establish the presence or absence of pulmonary embolism. Those with a low modified Wells clinical probability and a normal quantitative d-dimer finding were discharged home. All others followed a reference standard protocol using Prospective Investigation of Pulmonary Embolism Diagnosis-interpreted ventilation/perfusion scanning, CT pulmonary angiography, and digital subtraction pulmonary angiography. All patients were followed up clinically for 3 months.
  
  
  RESULTS
  For the Bohr calculation, the area under the receiver operating characteristic curve was 0.62 (95% confidence interval [CI], 0.51 to 0.73), the Enghoff calculation was 0.66 (95% CI, 0.55 to 0.77), and the capillary sample Enghoff was 0.62 (95% CI, 0.49 to 0.65). The optimum Bohr cutoff value gave 100.0% sensitivity (95% CI, 84.5 to 100%) but a low specificity of 22.7% (95% CI, 18.8 to 27.2%). The optimum cutoff points for Enghoff and capillary Enghoff calculations gave sensitivities of 95.3% (95% CI, 77.3 to 99.2%) and 94.4% (95% CI, 74.2 to 99.0%), respectively, with poor specificity.
  
  
  CONCLUSIONS
  Respiratory dead space analysis does not perform well as a stand-alone diagnostic test for pulmonary embolism in outpatients presenting with pleuritic chest pain.
authors.affiliation: Emergency Medicine Research Group, Emergency Department, Manchester Royal Infirmary, Oxford Rd, Manchester, M13 9WL UK. kerstinhogg@hotmail.com
authors.forename: Kerstin
authors.initials: K
authors.lastname: Hogg
authors.forename: Deborah
authors.initials: D
authors.lastname: Dawson
authors.forename: Ted
authors.initials: T
authors.lastname: Tabor
authors.forename: Beverly
authors.initials: B
authors.lastname: Tabor
authors.forename: Kevin
authors.initials: K
authors.lastname: Mackway-Jones
mesh_terms: D000328:Adult; D002245:Carbon Dioxide / Q000032:analysis; D004636:Emergency Service, Hospital; D004739:England; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010045:Outpatients; D010998:Pleurisy / Q000209:etiology*; D011336:Probability; D011446:Prospective Studies; D011650:Pulmonary Alveoli; D011655:Pulmonary Embolism / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology*; D015203:Reproducibility of Results; D012126:Respiratory Dead Space / Q000502:physiology; D012129:Respiratory Function Tests; D014057:Tomography, X-Ray Computed
chemical_list: D002245:Carbon Dioxide