Acute Respiratory Distress Syndrome (ARDS) is characterized by severe hypoxemia and extensive lung injury. Recent studies indicate that lung functional phenotypes - particularly the distribution and evolution of lung perfusion - may be closely related to patient outcomes. Electrical impedance tomography (EIT) offers non-invasive, bedside, real-time monitoring of lung perfusion patterns and enables classification into distinct phenotypes and trajectory types over the course of illness. To date, limited data exist on perfusion phenotype trajectories in ARDS patients and their relationship with clinical outcomes. This study seeks to characterize dynamic lung dynamic ventilation-perfusion functional Phenotype using EIT and explore their prognostic significance. Objectives

Primary Objective:

To identify lung perfusion phenotype trajectories in ARDS patients using EIT and assess their association with 28-day mortality.

Secondary Objectives:

• To determine the relationship between different trajectory types and improvements in oxygenation and respiratory mechanics.
• To investigate how ventilator settings (PEEP, driving pressure) interact with perfusion changes.
• To support individualized mechanical ventilation strategies based on Ventilation-Perfusion Functional Phenotype monitoring

Design: Prospective, multicenter, observational cohort study

• Setting: ≥2 tertiary ICUs equipped with EIT capability
• Population: Adult patients with moderate-to-severe ARDS (Berlin definition, PaO₂/FiO₂ ≤ 200 mmHg) receiving mechanical ventilation
• Intervention: Daily lung perfusion assessment using a 16-electrode EIT belt. Regional ventilation-perfusion (V/Q) ratios are calculated by combining tidal and pulsatile impedance changes. Phenotypes are classified as Matched V/Q, High V/Q (dead space), Low V/Q (shunt), or Globally Impaired V/Q. Trajectories are categorized as Stable, Improving, Deteriorating, or Fluctuating.
• Endpoints:
• Primary: Association between phenotype trajectory type and 28-day mortality
• Secondary: Time to oxygenation improvement, duration of mechanical ventilation, ICU length of stay, interaction between trajectory and ventilator settings

Inclusion Criteria:

• ge ≥ 18 years
• Moderate-to-severe ARDS (Berlin definition, PaO₂/FiO₂ ≤ 200 mmHg)
• Mechanically ventilated and eligible for EIT monitoring
• Informed consent obtained from patient or legal surrogate

Exclusion Criteria:

• Pregnancy
• Presence of implanted metallic devices interfering with EIT (e.g., pacemaker)
• Severe chest wall deformity or skin condition preventing electrode placement
• Expected survival < 24 hours

ARDS Mechanically Ventilated Patients