Acute Respiratory Distress Syndrome (ARDS) is characterized by severe hypoxemia and diffuse alveolar collapse, often requiring invasive mechanical ventilation. Non-individualized mechanical ventilation settings can cause ventilator-induced lung injury (VILI). Positive end-expiratory pressure (PEEP) prevents alveolar collapse, but its effect varies among individuals. The recruitment-to-inflation (R/I) ratio evaluates bedside lung recruitment potential. This pilot study aims to compare two individualized PEEP titration strategies-one guided by the best static respiratory compliance and another guided by transpulmonary pressure via an esophageal balloon-and evaluate how baseline lung recruitment potential alters the early physiological responses to these interventions. Both strategies are preceded by an identical, standardized pressure-controlled initial lung recruitment maneuver to establish a baseline recruitment state.
Diagnosis of moderate or severe Acute Respiratory Distress Syndrome (ARDS) according to the Berlin definition: acute onset, bilateral opacities not fully explained by heart failure or fluid overload, and Partial pressure of oxygen in arterial blood/Fraction of inspired oxygen <= 200 mmHg with Positive End-Expiratory Pressure (PEEP) >= 5 cmH2O.
ARDS duration < 36 hours since fully meeting Berlin consensus criteria.
Relative hemodynamic stability: absence of refractory shock, defined as norepinephrine dose <= 0.5 mcg/kg/min.
Evidence of active pulmonary air leaks (bronchopleural fistula, pneumothorax, pneumomediastinum).
Severe uncorrected hemodynamic instability (norepinephrine > 0.5 mcg/kg/min).
Contraindications for esophageal balloon placement (esophageal obstruction, known perforation, recent esophageal surgery, severe esophagitis).
Elevated intracranial pressure or conditions where hypercapnia-induced increases in intracranial pressure must be avoided (intracranial hemorrhage, cerebral contusion, cerebral edema, mass effect with midline shift on CT).
Parallel
Positive End-Expiratory Pressure (PEEP) Titration guided by Static Compliance
Procedure/SurgeryPositive End-Expiratory Pressure (PEEP) Titration by Static Compliance: Following the initial recruitment maneuver, an individualized PEEP decremental titration step-protocol is performed to identify the specific PEEP level that maximizes the static compliance of the respiratory system, aiming to optimize the balance between alveolar recruitment and overdistension. Initial Lung Recruitment Maneuver : Prior to individualized PEEP titration, all participants in this arm will undergo an initial standardized lung recruitment maneuver. This procedure will be executed in Pressure-Controlled Ventilation (PCV) mode, utilizing a driving/control pressure of 15 cmH2O. The recruitment process will begin at a baseline Positive End-Expiratory Pressure (PEEP) of 5 cmH2O, followed by incremental steps of 5 cmH2O every 10 seconds until reaching a maximum PEEP of 25 cmH2O. A peak airway pressure limit of 40 cmH2O will be strictly maintained during the maneuver for a total duration of 1 minute.
Positive End-Expiratory Pressure (PEEP) Titration guided by Transpulmonary Pressure
Procedure/SurgeryPositive End-Expiratory Pressure (PEEP) Titration by Transpulmonary Pressure: Following the initial recruitment maneuver, PEEP is titrated and protocolized via real-time esophageal balloon monitoring to target and maintain a slightly positive expiratory transpulmonary pressure, minimizing cyclic alveolar collapse and overdistension. Initial Lung Recruitment Maneuver: Prior to individualized PEEP titration, all participants in this arm will undergo an initial standardized lung recruitment maneuver. This procedure will be executed in Pressure-Controlled Ventilation (PCV) mode, utilizing a driving/control pressure of 15 cmH2O. The recruitment process will begin at a baseline Positive End-Expiratory Pressure (PEEP) of 5 cmH2O, followed by incremental steps of 5 cmH2O every 10 seconds until reaching a maximum PEEP of 25 cmH2O. A peak airway pressure limit of 40 cmH2O will be strictly maintained during the maneuver for a total duration of 1 minute.
Change in Early Oxygenation (PaO2/FiO2 Ratio).
The change in gas exchange efficiency is calculated as the absolute difference between the baseline Partial pressure of oxygen in arterial blood (PaO2)/Fraction of inspired oxygen (FiO2) ratio and the PaO2/FiO2 ratio measured 24 hours after individualized Positive End-Expiratory Pressure (PEEP) titration.
Evolution of Static Compliance of the Respiratory System
Changes in static compliance calculated via the formula: Tidal Volume / (Plateau Pressure - Positive End-Expiratory Pressure).
Evolution of Driving Pressure and Plateau Pressure
Serial monitoring of driving pressure (Plateau Pressure - Positive End-Expiratory Pressure) and plateau pressure to evaluate lung stress.
Ventilatory Efficiency
Evaluated using the Ventilatory Ratio (VR), which correlates physiological dead space and minute ventilation.
Incidence of Elevated Airway Opening Pressure (AOP)
Proportion of patients exhibiting an airway opening pressure greater than 5 cmH2O.
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