Inclusion Criteria:

• Adults aged ≥18 years.

• Presentation to the emergency department with acute dyspnea and acute respiratory failure, defined by at least one of the following:

  • PaO₂ < 60 mmHg on room air, or
  • Oxygen saturation (SpO₂) < 90% on room air, or
  • PaO₂/FiO₂ ratio < 300.

• Ability to provide written informed consent or eligibility for deferred consent according to local regulations.

• Undergoing standard diagnostic evaluation including laboratory tests and chest imaging as part of routine clinical care.

Exclusion Criteria:

• Refusal to provide informed consent (or consent by legal representative when applicable).
• Inadequate ultrasound window or technically insufficient ultrasound assessment.
• Acute respiratory failure secondary to chest trauma.
• Cardiac arrest at presentation or during emergency department stabilization.
• Requirement for invasive mechanical ventilation during initial stabilization in the emergency department.