Acute respiratory distress syndrome (ARDS) is a major cause of mortality in intensive care units. Prone position ventilation (PPV) is an important component of ARDS management and has been shown to reduce mortality in patients with moderate-to-severe ARDS. However, substantial heterogeneity exists in treatment response to PPV. Previous studies suggest that lung morphology-focal versus non-focal patterns based on chest CT-may influence responses to ventilatory strategies, but whether lung morphology modifies the effect of PPV remains unclear. In addition, the benefits and safety of PPV in patients with acute brain injury (ABI) complicated by ARDS are uncertain. Although PPV improves oxygenation, it may impair cerebral venous drainage and increase intracranial pressure, raising concerns about its use in ABI patients. Evidence from randomized trials in this population is limited and excludes patients with more severe hypoxemia or elevated intracranial pressure.

Furthermore, the optimal duration and termination criteria for PPV are not well established. While PPV improves alveolar recruitment and reduces ventilator-induced lung injury, prolonged PPV may lead to excessive sedation exposure and PPV-related complications. Identifying the appropriate timing to discontinue PPV may help balance clinical benefits and potential harms.This study is a prospective, multicenter registry enrolling patients with moderate-to-severe ARDS. The objectives are: (1) To determine whether lung morphology can guide individualized PPV strategies; (2) To evaluate the effectiveness and safety of PPV in patients with ARDS complicated by acute brain injury; (3) To investigate the optimal timing for termination of PPV through target trial emulation methods.In addition to these core objectives, the study will include other exploratory aims.

Inclusion Criteria:

1.Age ≥ 18 years 2. Moderate-to-severe ARDS requiring invasive mechanical ventilation, defined as:

1. PaO₂/FiO₂ ≤ 150 mm Hg,
2. PEEP ≥ 5 cm H₂O,
3. ARDS diagnosed according to the 2023 Global Definition.

Exclusion Criteria:

1.Refusal of informed consent by the patient's legally authorized representative

Moderate-to-severe ARDS