title: Concordance between capnography and arterial blood gas measurements of carbon dioxide in acute asthma.
abstract: OBJECTIVE
  We examine the concordance between end-tidal partial pressure of CO2 (PetCO2) measured by capnography and arterial partial pressure of carbon dioxide (PaCO2) obtained by arterial blood gas in acute asthmatic patients presenting to the emergency department.
  
  
  METHODS
  This was a prospective observational cohort study of acutely ill adult asthmatic patients undergoing an arterial blood gas measurement as part of their evaluation. PetCO2 was recorded during exhalation into a capnograph while arterial blood was pulsing in the arterial blood gas tubing. Concordance between PetCO2 and PaCO2 was displayed as a Bland-Altman matrix, using prespecified limits of agreement of +/-5 mm Hg difference between PetCO2 and PaCO2 in each patient.
  
  
  RESULTS
  The mean difference between the PetCO2 and PaCO2 levels was 1.0 mm Hg (95% confidence interval -0.1 to 2.0 mm Hg), with a median of 0 mm Hg. Of the 39 patients enrolled, 37 (95%) fell within the a priori limits of agreement.
  
  
  CONCLUSIONS
  In adult asthmatic patients with acute exacerbations, concordance between PetCO2 measured by capnography and PaCO2 measured by arterial blood gas was high. These findings must be validated before capnography replacement of arterial blood gas as an accurate means of assessing alveolar ventilation in acute asthma is recommended.
authors.affiliation: Department of Emergency Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA. jillcorbo@aol.com
authors.forename: Jill
authors.initials: J
authors.lastname: Corbo
authors.forename: Polly
authors.initials: P
authors.lastname: Bijur
authors.forename: Michael
authors.initials: M
authors.lastname: Lahn
authors.forename: E John
authors.initials: EJ
authors.lastname: Gallagher
mesh_terms: D000208:Acute Disease; D000328:Adult; D001249:Asthma / Q000145:classification / Q000175:diagnosis* / Q000378:metabolism*; D001784:Blood Gas Analysis; D019296:Capnography; D002245:Carbon Dioxide / Q000378:metabolism*; D015331:Cohort Studies; D004635:Emergency Medicine / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010366:Peak Expiratory Flow Rate; D017064:Process Assessment, Health Care; D011446:Prospective Studies; D012680:Sensitivity and Specificity
chemical_list: D002245:Carbon Dioxide