Acute dyspnea is a common reason for emergency department (ED) admission and is frequently caused by acute heart failure with pulmonary edema. Rapid differentiation between cardiogenic and non-cardiogenic causes of dyspnea is essential to guide early treatment and risk stratification. However, no single gold standard exists for the assessment of venous congestion in the acute setting.

This prospective observational study aims to evaluate the diagnostic accuracy of respiratory variation in inferior vena cava (IVC) diameter measured by point-of-care ultrasound (POCUS) in identifying acute pulmonary edema in patients presenting to the ED with acute respiratory failure. In addition, the study investigates whether integration of IVC ultrasound with lung ultrasound, bedside cardiac ultrasound, and selected clinical and laboratory variables - such as hemoglobin and plasma protein changes - improves diagnostic performance and prognostic stratification.

Acute heart failure is a leading cause of emergency department visits and hospital admissions and is associated with high morbidity, mortality, and healthcare costs. Dyspnea is the most frequent presenting symptom. Early identification of pulmonary edema and assessment of venous congestion are critical to optimize therapeutic decisions in the acute phase.

Ultrasound assessment of inferior vena cava (IVC) respiratory variation has been proposed as a rapid, non-invasive marker of volume overload and venous congestion. However, its reliability during the early stages of acute dyspnea remains uncertain, particularly in patients with increased respiratory effort. Other ultrasound-based approaches, including lung ultrasound, and focused cardiac ultrasound, provide complementary information on pulmonary congestion and cardiac function.

This single-center, prospective, observational study will enroll adult patients presenting to the emergency department with acute dyspnea and respiratory failure. All participants will undergo standardized clinical assessment, laboratory testing, chest imaging as per routine care, and multimodal point-of-care ultrasound evaluation at ED admission, after 1 hour, and at 24-48 hours when clinically feasible.

The primary objective is to assess the diagnostic accuracy of respiratory variation in IVC diameter for identifying acute pulmonary edema. Secondary objectives include evaluation of multimodal ultrasound-clinical scores for diagnostic and prognostic purposes and analysis of early changes in hemoglobin and plasma proteins as surrogate markers of fluid shifts. Clinical outcomes, including need for hospitalization, escalation of care, and in-hospital mortality, will be recorded.

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.

Adult patients presenting to the emergency department with acute dyspnea and acute respiratory failure, undergoing standard diagnostic evaluation and clinical management as part of routine care.

Results are reported only in aggregated form.