End-Tidal Carbon Dioxide as a Prognostic Feature in Pulmonary Arterial Hypertension

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).

Prior work has demonstrated that ETco₂ is lower in patients with PAH than in control patients, but whether ETco₂ has prognostic value is unknown. We hypothesized that lower measurements of ETco₂ in patients with PAH correlate with worse long-term outcomes.

Patients with PAH seen in our referral clinic were prospectively recruited for ETco₂ measurement between September 2009 and February 2010. Vital status as of July 2015 was documented using medical records and the Social Security Death Index.

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 ETco₂ in survivors was 30.5 ± 4.8 mm Hg, whereas mean ETco₂ in patients who died was 27.1 ± 4.2 mm Hg (P = 0.004). After stratification by median baseline ETco₂ of 29 mm Hg, survival in each group was analyzed. Patients with lower ETco₂ had shorter survival (P = 0.006). Cox regression analysis with ETco₂ as 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, ETco₂ was unchanged.

Our single-center data suggest that lower ETco₂ is associated with shorter survival and that ETco₂ is stable over time in patients with PAH.