Inspiratory Effort-Targeted Pressure Support Ventilation (IT-PSV) Trial

Mechanically ventilated patients, who are admitted to the ICU with acute hypoxic respiratory failure, will be consecutively screened daily at 08:00-10:00 morning rounds. Inclusion criteria: 1. PSV initiated during the last 24 hours; 2. Mechanical ventilation expected to be required for at least 24-48 h by responsible physicians; 3. The partial pressure of oxygen in arterial blood (PaO2)/inspired oxygen fraction (FiO2) ≤ 300 mmHg (measuring at clinical FiO2 and positive end-expiratory pressure PEEP); 4. No sedation or stable sedation with Richmond Agitation Sedation Scale (RASS) of -2 to +1 or Riker's Sedation-Agitation Scale (SAS) of 3 to 4. Exclusion criteria included: 1. Age younger than 18 years old; 2. Initiation of PSV before ICU admission; 3. Duration of mechanical ventilation longer than 7 days before enrollment; 4. History of neuromuscular diseases; 5. Clinical suspicion of increased intracranial pressure; 6. Extracorporeal support; 7. Moribund conditions; 8. Refusal by the ICU physicians or the patient.