Supplemental oxygen for pulmonary embolism (SO-PE): study protocol for a mechanistic, randomised, blinded, cross-over study

Background: Acute pulmonary embolism (PE) mortality is linked to abrupt rises in pulmonary artery (PA) pressure due to mechanical obstruction and pulmonary vasoconstriction, leading to right ventricular (RV) dilation, increased RV wall tension and oxygen demand, but compromised right coronary artery oxygen supply. Oxygen is a known pulmonary vasodilator, and in preclinical animal models of PE, supplemental oxygen reduces PA pressures and improves RV function. However, the mechanisms driving these interactions, especially in humans, remain poorly understood. The overall objective of the supplemental oxygen in pulmonary embolism (SO-PE) study is to investigate the mechanisms of supplemental oxygen in patients with acute PE.

Methods and analysis: This randomised, double-blind, cross-over trial at Massachusetts General Hospital will include adult patients with acute PE and evidence of RV dysfunction but without hypoxaemia (SaO₂ ≥90% on room air). We will enrol 80 patients, each serving as their own control, with 40 randomised to start on supplemental oxygen, and 40 randomised to start on room air. Over 180 min, patients will alternate between supplemental oxygen delivered by non-rebreather mask (60% FiO₂) and room air (21% FiO₂). The primary outcome will be the difference in pulmonary artery systolic pressure with and without oxygen. Secondary outcomes include additional echocardiographic measures, metabolomic profiles, vital signs and dyspnoea scores. Echocardiographic data will be compared by a paired t-test or Wilcoxon signed-rank test. For metabolomic analyses, we will perform multivariable mixed effects logistic regression models and calculate false discovery rate (q-value ≤0.05) to account for multiple comparisons. Data will be collected in compliance with National Institutes of Health and National Heart Lung and Blood Institute (NHLBI) policies for data and safety monitoring.

Ethics and dissemination: The SO-PE study is funded by the NHLBI and has been approved by the Institutional Review Board of Mass General Brigham (no. 2023P000252). The study will comply with the Helsinki Declaration on medical research involving human subjects. All participants will provide prospective, written informed consent.

Trial registration number: NCT05891886.