Acute Respiratory Distress Syndrome (ARDS) is a syndrome characterized by respiratory distress and refractory hypoxemia caused by pulmonary and extra-pulmonary factors. Despite improvements in diagnosis and treatment in recent years, the mortality rate of severe ARDS is still around 40%. The distribution of lung lesions in ARDS patients is significantly gravity-dependent. Even with lung-protective ventilation strategies, tidal volume is concentrated in the ventral lung region, leading to ventilator-associated lung injury. Prone position ventilation can increase ventilation to the dorsal lung tissue and improve the ventilation-perfusion ratio, thus improving oxygenation. During prone position ventilation in ARDS patients, lung-protective ventilation strategies should be maintained, but with different respiratory mechanics from the supine position, requiring adjustment of ventilator parameters. Electrical Impedance Tomography (EIT) technology can be used for bedside monitoring of mechanically ventilated patients, providing real-time feedback on the patient's ventilation status and having great potential for clinical applications. Investigators believes that EIT monitoring during prone position ventilation in ARDS patients can individualize lung-protective ventilation strategies, minimize alveolar overdistension and collapse, improve the weaning success rate of invasive ventilation, and ultimately improve patient prognosis.

Inclusion Criteria:

1. Age ≥ 18 years old；
2. Meets the diagnostic criteria for ARDS according to the 2012 Berlin definition；
3. Intubation with invasive mechanical ventilation time < 36 hours；
4. PaO2/FiO2 < 150mmHg.

Exclusion Criteria:

1. Contraindication to the prone position;
2. Contraindication to the EIT;
3. Patients have received extracorporeal membrane oxygenation treatment.