How I do it practically

Ashbaugh et al. (1967) proposed the first ARDS description, based on refractory hypoxemia, bilateral pulmonary infiltrates (X-ray), low respiratory system compliance, increased lung weight. In the years other definitions have been introduced, being the most widely accepted one the definition proposed by the American-European Consensus Conference which relies primarily on PaO2/FiO2 < 300 and bilateral infiltrates. Despite the diagnostic accuracy of these definitions has been validated they resulted in quite poor sensitivity/specificity. All the definitions available include the presence of bilateral pulmonary infiltrates as a surrogate of inflammatory lung edema. Unfortunately, the chest X-ray \u201cinfiltrates\u201d may derive from atelectasis, interstitial or intra-acinar edema or consolidation. In contrast analysis of Computed Tomography (CT) images may provide a better indicator of lung edema. New insights were provided by the CT-scan over the last two decades, demonstrating that ARDS does not homogeneously affect the lung parenchyma. The lung injury severity is widely distributed in ARDS population (5 to 70% of the total lung weight) and it is strictly associated with the severity of injury: greater is the amount of gasless tissue at 5 cmH2O PEEP, greater is the amount of gasless tissue regaining aeration at 45 cmH2O airway pressure. The lung CT findings may provide a firm rationale for tailoring tidal volume (VT) and PEEP during mechanical ventilation. VT should be set according to the lung open to ventilation rather than to the body weight. PEEP should be evaluated on the basis of lung recruitability: higher PEEP should be applied in patients with higher recruitability, lower PEEP in patients with lower recruitability