title: End-Tidal Carbon Dioxide as a Prognostic Feature in Pulmonary Arterial Hypertension.
abstract: BACKGROUND
  Pulmonary arterial hypertension (PAH) is characterized in part by increased dead space ventilation, which can be estimated noninvasively at the bedside by measurement of end-tidal CO2(ETco2).
  
  
  OBJECTIVE
  Prior work has demonstrated that ETco2is lower in patients with PAH than in control patients, but whether ETco2has prognostic value is unknown. We hypothesized that lower measurements of ETco2in patients with PAH correlate with worse long-term outcomes.
  
  
  METHODS
  Patients with PAH seen in our referral clinic were prospectively recruited for ETco2measurement between September 2009 and February 2010. Vital status as of July 2015 was documented using medical records and the Social Security Death Index.
  
  
  RESULTS
  Eighty-two patients were followed for a median of 60 months. Twenty-six patients died, and two were lost to follow-up. Patients who died were more likely to be older (58.5 ± 14.9 vs. 47.6 ± 12.2 yr; P < 0.05) and to have shorter 6-minute walk distance (296 ± 127 vs. 401 ± 92 m; P < 0.05). Mean ETco2in survivors was 30.5 ± 4.8 mm Hg, whereas mean ETco2in patients who died was 27.1 ± 4.2 mm Hg (P = 0.004). After stratification by median baseline ETco2of 29 mm Hg, survival in each group was analyzed. Patients with lower ETco2had shorter survival (P = 0.006). Cox regression analysis with ETco2as a continuous variable revealed the hazard ratio to be 0.88 (95% confidence interval, 0.80-0.97; P = 0.006). In 52 patients with more than one measurement a median of 17 months apart, ETco2was unchanged.
  
  
  CONCLUSIONS
  Our single-center data suggest that lower ETco2is associated with shorter survival and that ETco2is stable over time in patients with PAH.
authors.affiliation: 1 Division of Internal Medicine.
authors.forename: Caitlin E
authors.initials: CE
authors.lastname: Welch
authors.affiliation: 2 Division of Cardiovascular Medicine.
authors.forename: Evan L
authors.initials: EL
authors.lastname: Brittain
authors.affiliation: 3 Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Newman
authors.affiliation: 3 Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Ivan M
authors.initials: IM
authors.lastname: Robbins
authors.affiliation: 3 Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Meredith E
authors.initials: ME
authors.lastname: Pugh
authors.affiliation: 3 Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: John H
authors.initials: JH
authors.lastname: Newman
authors.affiliation: 3 Division of Allergy, Pulmonary and Critical Care Medicine, Vanderbilt University Medical Center, Nashville, Tennessee.
authors.forename: Anna R
authors.initials: AR
authors.lastname: Hemnes
mesh_terms: D000328:Adult; D000368:Aged; D002245:Carbon Dioxide / Q000032:analysis*; D005260:Female; D006801:Humans; D006976:Hypertension, Pulmonary / Q000401:mortality* / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D000067716:Point-of-Care Testing; D011379:Prognosis; D016016:Proportional Hazards Models; D011446:Prospective Studies; D016019:Survival Analysis; D013714:Tennessee / Q000453:epidemiology; D000070857:Walk Test
chemical_list: D002245:Carbon Dioxide
keywords: end-tidal carbon dioxide; pulmonary hypertension; survival