Overview

Assisted mechanical ventilation is widely used to preserve diaphragmatic activity and improve lung aeration in patients with acute respiratory failure. However, during assisted ventilation, excessive inspiratory effort may develop and contribute to lung injury, diaphragmatic overload, and patient self-inflicted lung injury.

Optimizing ventilator settings to modulate respiratory effort therefore represents a major physiological and clinical challenge.

Positive end-expiratory pressure (PEEP) is a key determinant of lung recruitment and respiratory system mechanics and may influence inspiratory effort by modifying lung volume, compliance, and respiratory drive. Despite its widespread use, PEEP titration in clinical practice is still mainly guided by oxygenation parameters, while its direct effects on inspiratory effort during assisted mechanical ventilation remain insufficiently characterized.

This physiological randomized crossover study aims to evaluate the effect of four predefined levels of positive end-expiratory pressure (0, 5, 10, and 15 cmH₂O) on the respiratory system and inspiratory effort in adult patients receiving assisted mechanical ventilation. Patients will be exposed to each PEEP level in randomized order, with stabilization and washout periods between conditions, while ventilatory support settings other than PEEP are kept constant.

Eligibility

Inclusion criteria:

• Age ≥18 years.
• ICU patients receiving invasive mechanical ventilation (endotracheal tube or tracheostomy).
• Ventilated in an assisted mode with spontaneous breathing
• Clinically stable to undergo protocolized PEEP changes.
• Sedation level compatible with spontaneous breathing and ventilator triggering
• Informed consent from the patient or legally authorized representative.

Exclusion Criteria:

• Contraindication to esophageal balloon placement (if applicable).
• Significant hemodynamic instability or unstable vasopressor requirements.
• Unstable arrhythmia or active myocardial ischemia.
• Undrained pneumothorax or major air leak.
• Controlled ventilation without effective spontaneous effort (apnea, neuromuscular blockade, deep sedation).
• Pregnancy
• Acute or chronic neurological conditions that may impair respiratory drive or interfere with the regulation of spontaneous breathing.