Pulmonary hypertension with a low cardiac index requires a higher PaO₂ level to avoid tissue hypoxia

The optimal oxygen supplementation needed to avoid tissue hypoxia in patients with pulmonary hypertension (PH) remains unclear. This study aimed to identify the arterial oxygen tension (PaO₂ ) level needed to avoid tissue hypoxia which results in a poor prognosis in patients with PH.

We retrospectively analysed the data for 1571 right heart catheterizations in patients suspected of having PH between 1983 and 2017 at our institution. Examinations were classified according to mean pulmonary arterial pressure (mPAP), cardiac index (CI) and the presence of lung disease, pulmonary arterial hypertension (PAH) or chronic thromboembolic PH (CTEPH). The PaO₂ levels needed to avoid tissue hypoxia were compared in each subgroup.

The estimated PaO₂ equivalent to a mixed venous oxygen tension (PvO₂ ) of 35 mm Hg (tissue hypoxia) was 63.2 mm Hg in all patients, 77.0 mm Hg in those with decreased CI (<2.5 L/min/m² ) and 57.0 mm Hg in those with preserved CI. Multivariate regression analysis identified mPAP, CI and PaO₂ to be independent predictors of extremely low PvO₂ . Similar results were observed regardless of the severity of PH or the presence of lung disease, PAH or CTEPH. The PaO₂ level needed to avoid tissue hypoxia was higher in patients with mild PH and decreased CI than in those with severe PH and preserved CI (70.2 vs 61.5 mm Hg).

These findings indicate that a decreased CI rather than increased mPAP induces tissue hypoxia in PH. Patients with PH and decreased CI may need adjustment of oxygen therapy at higher PaO₂ levels compared with patients with preserved CI.