In ARDS patients, mechanical ventilation should minimize ventilator-induced lung injury. The mechanical power which is the energy per unit time released to the respiratory system according to the applied tidal volume, PEEP, respiratory rate, and flow should reflect the ventilator-induced lung injury

Mechanical ventilation is an essential tool for the treatment of patients with acute respiratory distress syndrome (ARDS); however, as other strategies, it is not free of complications. Inadequate ventilation may have a negative impact on the lung that may eventually cause the development of multiple organ failure and death. This process is known as ventilator-induced lung injury (VILI). From a clinical perspective, one of the most important objectives of ARDS treatment is to avoid or mitigate the development of VILI, not only to preserve pulmonary integrity, but also to reduce mortality.

Ventilator-induced lung injury results from the interaction between the mechanical load applied to the lung and its capacity to tolerate it. Factors such as tidal volume (Vt), plateau pressure (PPlat), lung strain or insufflation pressure (ΔP), inspiratory flow rate (VI), respiratory rate (RR), excessive inspiratory effort, high levels of FiO2 and high levels of positive end-expiratory pressure (PEEP), have been directly involved in damage mechanism. With an integrating and rheological idea, the concept of mechanical power tries to encompass the majority of these factors within a measurable unit in joules per minute, as the expression of power applied on a repetitive basis on the respiratory system in ARDS. Although the concept of MP holds promise for preventing the risk of VILI, its utility has not been proven in clinical practice until now. The main value of MP over the rest of commonly used variables for the monitoring of patients with ARDS is that it includes flow on injury mechanism (kinetic energy), accepting that an inverse relationship exists between this mechanism and the capacity of alveoli to adapt to change during the ventilation cycle (strain rate), as well as it embodies the concept of process repeatability (respiratory rate), though not of its duration. This begs the question whether we should consider its value at the moment of defining a mechanical ventilation strategy. The main disadvantage of its application is that MP conceives the respiratory system in an integrated manner and not related to or standardized with the ventilable lung portion, that is ultimately the one who has to withstand the ventilatory load; in other words, the same MP may have different consequences depending on the baby lung size or its equivalent, the severity of ARDS.

The objective of this study is to evaluate the influence of the ventilable lung size on VILI mechanisms in patients suffering from ARDS treated with protective ventilation with similar MP.

Inclusion Criteria: patients consecutively admitted with ARDS -

Exclusion Criteria: Patients who meet any of the following criteria: history of emphysema, asthma, pneumothorax or bronchopleural fistula. Severe instability condition at the time of the study: SaO2 ≤90%, shock requiring noradrenaline ≥0,5 γ/kg/min, ventricular arrhythmia, myocardial ischemia and endocranial hypertension. Esophageal pathology that contraindicates esophageal balloon placement. Severe coagulopathy (platelet count <20000/mm3 or INR >4). Inability to undergo CT imaging: morbid obesity (≥170 kg) or abdominal girth >200 cm. Patients with do-not-resuscitate (DNR) orders, pregnant women and those who participated in other research studies within the last 30 days.

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patients consecutively admitted with ARDS, as defined according to the Berlin expert consensus