Blood Carbon Dioxide Tension and Risk in Pulmonary Arterial Hypertension

Background: Low partial pressure of blood carbon dioxide (PCO) is common in patients with pulmonary arterial hypertension (PAH) and may inform on clinical outcomes. We investigated whether PCO measurements could provide prognostic information in addition to standard risk assessment in this group of patients.

Methods: We conducted a retrospective observational cohort study on patients with newly diagnosed idiopathic, heritable or drug/toxin-induced PAH recruited from two European centres. Arterialised capillary blood gas analyses at diagnosis and follow-up were incorporated into standard risk assessment strategies and related to outcomes, defined as lung transplant or death. C statistics from receiver-operated characteristics and Cox regression models were used to assess the predictive value of models with and without PCO measurements. Unsupervised clustering was applied to assess the relation of PCO to haemodynamic and pulmonary function variables.

Results: Low PCO measured at diagnosis and follow-up was significantly associated with inferior outcomes in 204 patients with PAH. PCO provided prognostic information independent of established non-invasive variables. Integrating PCO in risk strata improved C statistics of non-invasive and mixed invasive/non-invasive models, and revealed more accurate outcome estimates in regression models. Pairwise correlation and unsupervised cluster analyses supported a link between PCO and haemodynamic variables, particularly with cardiac output, in PAH.

Conclusions: Measuring PCO at diagnosis and during follow-up in patients with PAH provided independent prognostic information and has the potential to improve current risk assessment strategies.