title: D-dimer and exhaled CO2/O2 to detect segmental pulmonary embolism in moderate-risk patients.
abstract: BACKGROUND
  Pulmonary embolism (PE) decreases the exhaled end-tidal ratio of carbon dioxide to oxygen (etCO(2)/O(2)).
  
  
  OBJECTIVE
  To test if the etCO(2)/O(2) can produce clinically important changes in the probability of segmental or larger PE on computerized tomography multidetector-row pulmonary angiography (MDCTPA) in a moderate-risk population with a positive D-dimer.
  
  
  METHODS
  Emergency department and hospitalized patients with one or more predefined symptoms or signs, one or more risk factors for PE, and 64-slice MDCTPA enrolled from four hospitals. D-dimer greater than 499 ng/ml was test(+), and D-dimer less than 500 ng/ml was test(-). The median etCO(2)/O(2) less than 0.28 from seven or more breaths was test(+) and etCO(2)/O(2) greater than 0.45 was test(-). MDCTPA images were read by two independent radiologists and the criterion standard was the interpretation of acute PE by either reader. PE size was then graded.
  
  
  RESULTS
  We enrolled 495 patients, including 60 (12%) with segmental or larger, and 29 (6%) with subsegmental PE. A total of 367 (74%) patients were D-dimer(+), including all 60 with segmental or larger PE (posterior probability 16%). The combination of D-dimer(+) and etCO(2)/O(2)(+) increased the posterior probability of segmental or larger PE to 28% (95% confidence interval [CI] for difference of 12%, 3.0-22%). The combination of D-dimer(+) and etCO(2)/O(2)(-) was observed in 40 patients (8%; 95% CI, 6-11%), and none (0/40; 95% CI, 0-9%) had segmental or larger PE on MDCTPA. No strategy changed the prevalence of subsegmental PE.
  
  
  CONCLUSIONS
  In moderate-risk patients with a positive D-dimer, the et etCO(2)/O(2) less than 0.28 significantly increases the probability of segmental or larger PE and the etCO(2)/O(2) greater than 0.45 predicts the absence of segmental or larger PE on MDCTPA.
authors.affiliation: Department of Emergency Medicine, Carolinas Medical Center, 1000 Blythe Boulevard, Charlotte, NC 28203, USA. Jkline@carolinas.org
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Kline
authors.forename: Melanie M
authors.initials: MM
authors.lastname: Hogg
authors.forename: D Mark
authors.initials: DM
authors.lastname: Courtney
authors.forename: Chadwick D
authors.initials: CD
authors.lastname: Miller
authors.forename: Alan E
authors.initials: AE
authors.lastname: Jones
authors.forename: Howard A
authors.initials: HA
authors.lastname: Smithline
authors.forename: Nicole
authors.initials: N
authors.lastname: Klekowski
authors.forename: Randy
authors.initials: R
authors.lastname: Lanier
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019296:Capnography; D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D045853:Exhalation; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000000981:diagnostic imaging / Q000378:metabolism*; D036542:Tomography, Spiral Computed; D055815:Young Adult
chemical_list: D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D; D002245:Carbon Dioxide; D010100:Oxygen
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