Acute respiratory distress syndrome (ARDS) is a life-threatening disease, patients with ARDS usually need mechanical ventilation. The treatment of ARDS include low tidal volume ventilation, steroid, extracorporeal membraneous oxygenator, inhaled nitric oxide or prone position . Some studies showed prone position had beneficial effect of oxygenation and mortality for severe ARDS patients, the duration of prone position should be at least 10 hours. It is unknown the optimal duration of prone position which is better for severe ARDS patients. This study will compare the clinical differences of 16-hour and 24-hour prone position for severe ARDS patients.

This is a prospective randomized controlled study. All severe ARDS patients were eligible for screening from January 2020 to December 2022. Inclusion criteria include: Patient above 20 year-old with diagnosis of severe ARDS under protective lung ventilation( tidal volume 4-8 ml/kg, plateau pressure < 30cm H2O、PaO2/FiO2 < 150 mmHg、PEEP ≥ 5 cmH2O、FiO2 > 60%）. Patients were excluded if patients were not intubated and mechanically ventilated or contraindication for prone position ventilation (intracranial hemorrhage, massive hemoptysis, unstable hemodynamic status, recent pacemaker implantation, severe facial laceration, open abdominal wound, spine, femur or pelvis fracture or pregnancy). Patients will divide into 2 groups, one is patients supported by 16-hour prone position; another group is patients with 24-hour prone position, each group enrolled 30 patients. The medical records of these patients were analyzed for age, gender, body weight, diagnosis, pulmonary or extrapulmonary ARDS, acute physiology and chronic health evaluation (APACHE) Ⅱscore, days between ARDS to prone position, ICU day, hospital day, ventilator day, pre and post prone position vital signs, laboratory data including arterial blood gas, lactate, respiratory parameters included PaO2/FiO2, peak inspiratory pressure, positive end-expiratory pressure, ventilator mode, steroid treatment, complications (tube dislodge, pressure sore, infection), and mortality outcomes.

The primary endpoint is the difference of oxygenation (PaO2/FiO2), the secondary endpoint are other respiratory parameters, vital signs, ICU day, hospital day, ventilator day, complications and survival.

Inclusion Criteria:

• Patient above 20 year-old with diagnosis of severe ARDS under protective lung ventilation (tidal volume 4-8 ml/kg, plateau pressure < 30cm H2O、PaO2/FiO2 < 150 mmHg、PEEP ≥ 5 cmH2O、FiO2 > 60%).

Exclusion Criteria:

• Patients were not intubated and mechanically ventilated or contraindication for prone position ventilation (intracranial hemorrhage, massive hemoptysis, unstable hemodynamic status, recent pacemaker implantation, severe facial laceration, open abdominal wound, spine, femur or pelvis fracture or pregnancy).