Acute pulmonary embolism (PE) often causes hypoxemic respiratory failure through ventilation-perfusion mismatch and right-ventricular (RV) strain; supportive oxygenation plus prompt anticoagulation are crucial to care . Current guidelines advise supplemental oxygen and escalation according to hemodynamic/respiratory status, but do not identify an optimal noninvasive modality for PE-related respiratory failure.

Acute pulmonary embolism (PE) often causes hypoxemic respiratory failure through ventilation-perfusion mismatch and right-ventricular (RV) strain; supportive oxygenation plus prompt anticoagulation are crucial to care . Current guidelines advise supplemental oxygen and escalation according to hemodynamic/respiratory status, but do not identify an optimal noninvasive modality for PE-related respiratory failure .. Non-invasive ventilation (NIV) can correct hypoxemia, yet applied positive pressure may adversely affect RV preload/afterload in PE and is frequently limited by intolerance . High-flow nasal cannula (HFNC) provides heated, humidified flows up to 60 L/min, improves oxygenation, reduces work of breathing, and enhances comfort versus conventional oxygen; in general hypoxemic acute respiratory failure (AHRF), HFNC reduced escalation and intubation compared with standard oxygen and, in some analyses, performed at least as well as NIV . Evidence specific to PE is emerging: a retrospective cohort and case series reported rapid improvements in oxygenation and respiratory distress with HFNC, with good tolerance and no major hemodynamic compromise. By avoiding mask-related intolerance and reducing harmful intrathoracic pressure effects while delivering consistent high FiO₂ and modest PEEP, HFNC may facilitate faster de-escalation and better outcomes than NIV in PE-related AHRF, a population for whom definitive comparative trials are lacking.

Inclusion Criteria:

- 1. Age ≥18 y; presented with acute PE confirmed by CTPA or high-probability V/Q.

2. AHRF needing non-invasive support; provided that patients able to protect airway and hemodynamically stable without escalating vasopressors

Exclusion Criteria:

• 1. Immediate indication for intubation; high-risk (massive) PE with shock requiring advanced airway/vasopressors; active major bleeding; untreated pneumothorax.

  2. Contraindications/intolerance to assigned modality (e.g., facial trauma for NIV; complete nasal obstruction for HFNC).

  3. Do-Not-Intubate orders; pregnancy ; concomitant respiratory failure primarily due to another process requiring a different pathway.