Blood carbon dioxide tension and risk in pulmonary arterial hypertension

Low partial pressure of blood carbon dioxide (P_aCO₂) is common in patients with pulmonary arterial hypertension (PAH) and may inform on clinical outcomes. We investigated whether P_aCO₂ measurements could provide prognostic information in addition to standard risk assessment in this group of patients.

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 P_aCO₂ measurements. Unsupervised clustering was applied to assess the relation of P_aCO₂ to haemodynamic and pulmonary function variables.

Low P_aCO₂ measured at diagnosis and follow-up was significantly associated with inferior outcomes in 204 patients with PAH. P_aCO₂ provided prognostic information independent of established non-invasive variables. Integrating P_aCO₂ 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 P_aCO₂ and haemodynamic variables, particularly with cardiac output, in PAH.

Measuring P_aCO₂ at diagnosis and during follow-up in patients with PAH provided independent prognostic information and has the potential to improve current risk assessment strategies.