Acute respiratory distress syndrome (ARDS) is characterized by acute diffuse alveolar injury caused by a variety of pulmonary and extrapulmonary factors, leading to refractory hypoxemia. It has high incidence and mortality rates. Neuromuscular blocking agents (NMBAs) play a crucial role as adjunctive therapy for ARDS, aiding in lung-protective ventilation by inhibiting excessive spontaneous breathing, improving patient-ventilator synchrony, and reducing barotrauma. Determining the appropriate depth of muscle relaxation in moderate to severe ARDS patients receiving NMBAs remains a clinical challenge. Research has shown that partial neuromuscular blockade is feasible in certain ARDS patients. However, large randomized controlled trials (RCTs) and clinical practices often use higher doses of NMBAs to ensure complete cessation of spontaneous breathing. This indicates an ongoing debate regarding the optimal depth of neuromuscular blockade necessary for lung-protective ventilation in ARDS patients. It also raises the question of whether the optimal depth of neuromuscular blockade varies among patients with different severities of ARDS. This study aims to investigate changes in respiratory mechanics and other physiological parameters in moderate to severe ARDS patients under different depths of neuromuscular blockade. The investigators will evaluate the impact of targeted neuromuscular blockade depth on lung protection in these patients.