The aim of this study is to make analysis of potentially modifiable factors contributing to outcome of mechanically ventilated ARDS adult patient receiving lung protective strategy.

Primary Objective: is to evaluate whether DP was superior to the variables that define it in predicting hospital outcome including mortality.

Secondary Objective: is to identify manageable factors associated with outcome such as ventilator-related parameters and to investigate the role of non-modifiable factors such as demographic characteristics, severity of illness.

The acute respiratory distress syndrome (ARDS) is an acute and intense inflammatory disease process of the Lungs, characterized clinically by severe hypoxemia and bilateral pulmonary infiltrates. The hospital mortality ranges between 35% and 45% (1). Traditionally, critically ill patients requiring mechanical ventilation (MV) were ventilated using high tidal volumes (Vt) and high airway pressures, until the pivotal ARDS net randomized controlled trial (RCT) demonstrated that a "lung-protective" MV strategy using a Vt of 4-8 mL/kg predicted body weight (PBW) and moderate levels of positive end-expiratory pressure (PEEP) improved survival (2).

The driving pressure (DP) (calculated as the Pplat minus applied PEEP) has been suggested as a major determinant for the beneficial effects of the three main components of lung-protective MV, namely, Vt, Pplat, and PEEP. and also a given DP would have different effects on outcome depending on the Vt, Pplat, and PEEP (3).

A retrospective analysis of several trials in patients with ARDS comparing different PEEP levels at the same VT or different VT levels at the same PEEP, or a combination of both, found that ΔPrs is the stronger predictor of mortality as compared with Pplats (3).

Inclusion Criteria:

• ARDS Patients: who are treated with lung-protective MV and assessed on standardized ventilatory settings(4) at 24 hours after ARDS onset . All patients will meet the American-European Consensus Conference criteria for ARDS (5) on PEEP greater than or equal to 5 cm H2O and Berlin criteria for moderate or severe ARDS (6).

Exclusion Criteria:

• Patients with left atrial hypertension, as diagnosed by the attending physician, as the primary cause of respiratory failure.
• Anticipated duration of mechanical ventilation of less than 48 hours.
• Severe chronic respiratory disease; neuromuscular disease that would prolong mechanical ventilation.
• Intracranial hypertension; morbid obesity; pregnancy.

Inclusion criteria:

ARDS Patients: who are treated with lung-protective MV and assessed on standardized ventilatory settings(4) at 24 hours after ARDS onset . All patients will meet the American-European Consensus Conference criteria for ARDS (5) on PEEP greater than or equal to 5 cm H2O and Berlin criteria for moderate or severe ARDS (6).

Exclusion criteria:

• Patients with left atrial hypertension, as diagnosed by the attending physician, as the primary cause of respiratory failure.
• Anticipated duration of mechanical ventilation of less than 48 hours.
• Severe chronic respiratory disease; neuromuscular disease that would prolong mechanical ventilation.
• Intracranial hypertension; morbid obesity; pregnancy.