Acute Respiratory Distress Syndrome (ARDS) is a highly lethal disease with limited treatment options. In recent years, prone position ventilation has been shown to improve the mortality rate and lung injury of ARDS patients by promoting lung recruitment, improving ventilation/perfusion (V/Q) ratio, enhancing respiratory system compliance, promoting sputum drainage, and effectively avoiding overinflation of the dorsal lung. Electrical Impedance Tomography (EIT) technology has been used to evaluate the effect of prone position ventilation on lung V/Q matching, and some studies have confirmed that prone position ventilation can improve lung V/Q matching and oxygenation index. However, previous studies were mostly case reports or small-sample physiological studies that lacked dynamic changes in lung V/Q matching during repeated prone position ventilation. Therefore, this study hypothesizes that prone position ventilation can increase lung V/Q matching in ARDS patients, and its improvement is correlated with changes in oxygenation index, invasive ventilation time, and patient prognosis. Repeated prone position ventilation can maintain lung V/Q matching at a higher level, no longer affected by changes in body position, which can accelerate pulmonary function recovery and improve the prognosis of ARDS patients.

Inclusion Criteria:

1. Age ≥ 18 years old;
2. meet the diagnostic criteria of Berlin's definition for ARDS;
3. invasive ventilation time < 48h;
4. PaO2/FiO2 < 150mmHg.

Exclusion Criteria:

1. Contraindication to the prone position;
2. Contraindication to the EIT;
3. Hemodynamically unstable;
4. Patients with hypernatremia;
5. Patients have received extracorporeal membrane oxygenation treatment.

ARDS Patients with PaO2/FiO2 < 150mmH