title: Prehospital end-tidal carbon dioxide differentiates between cardiac and obstructive causes of dyspnoea.
abstract: BACKGROUND
  Differentiating between cardiac and obstructive causes for dyspnoea is essential for proper management, but is difficult in the prehospital setting.
  
  
  OBJECTIVE
  To assess if prehospital levels of end-tidal carbon dioxide (ETCO2) differed in obstructive compared to cardiac causes of dyspnoea, and could suggest one diagnosis over the other.
  
  
  METHODS
  We conducted a retrospective cohort study among patients transported by emergency medical services during a 29-month period who were diagnosed with either obstructive pulmonary disease or congestive heart failure (CHF) by ICD-9 codes. Initial prehospital vital signs, including ETCO2, were recorded. Records were linked by manual archiving of emergency medical services and hospital data.
  
  
  RESULTS
  There were 106 patients with a diagnosis of obstructive or cardiac causes of dyspnoea that had prehospital ETCO2 levels measured during the study period. ETCO2 was significantly lower in patients diagnosed with CHF (31 mm Hg 95% CI 27 to 35) versus obstructive pulmonary disease (39 mm Hg 95% CI 35 to 42; p<0.001). Lower ETCO2 levels predicted CHF, with an area under the Receiver Operating Characteristics Curve of 0.70 (95% CI 0.60 to 0.81). Using ETCO2 <40 mm Hg as a cut-off, the sensitivity for predicting heart failure was 93% (95% CI 88% to 98%), the specificity was 43% (95% CI 33% to 52%), the positive predictive value was 38% (95% CI 29% to 48%), and the negative predictive value was 94% (95% CI 89% to 99%).
  
  
  CONCLUSIONS
  Lower levels of ETCO2 were associated with CHF, and may serve as an objective diagnostic adjunct to predict this cause of dyspnoea in the prehospital setting.
authors.affiliation: Department of Emergency Medicine, Orlando Regional Medical Center, Orlando, Florida, USA.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Hunter
authors.affiliation: Department of Emergency Medicine, Orlando Regional Medical Center, Orlando, Florida, USA.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Silvestri
authors.affiliation: Department of Emergency Medicine, Orlando Regional Medical Center, Orlando, Florida, USA.
authors.forename: George
authors.initials: G
authors.lastname: Ralls
authors.affiliation: Department of Emergency Medicine, Orlando Regional Medical Center, Orlando, Florida, USA.
authors.forename: Linda
authors.initials: L
authors.lastname: Papa
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001249:Asthma / Q000150:complications / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D004417:Dyspnea / Q000209:etiology* / Q000378:metabolism*; D004632:Emergency Medical Services; D005260:Female; D006333:Heart Failure / Q000150:complications / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications / Q000378:metabolism*; D012129:Respiratory Function Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013990:Tidal Volume / Q000502:physiology
chemical_list: D002245:Carbon Dioxide
keywords: COPD; Emergency Ambulance Systems; Heart Failure; Paramedics, Clinical Management; Pre-Hospital