Mechanical power ratio threshold for ventilator-induced lung injury

Abstract Rationale Mechanical power (MP) is a summary variable incorporating all causes of ventilator-induced-lung-injury (VILI). We expressed MP as the ratio between observed and normal expected values (MPratio). Objective To define a threshold value of MPratio leading to the development of VILI. Methods In a population of 82 healthy pigs, a threshold of MPratio for VILI, as assessed by histological variables and confirmed by using unsupervised cluster analysis was 4.5. The population was divided into two groups with MPratio above or below the threshold. Measurements and main results We measured physiological variables every six hours. At the end of the experiment, we measured lung weight and wet-to-dry ratio to quantify edema. Histological samples were analyzed for alveolar ruptures, inflammation, alveolar edema, atelectasis. An MPratio threshold of 4.5 was associated with worse injury, lung weight, wet-to-dry ratio and fluid balance (all p 4.5 MPratio in healthy lungs subjected to 48 h of mechanical ventilation appears to be a threshold for the development of ventilator-induced lung injury, as indicated by the convergence of histological, physiological, and anatomical alterations. In humans and in lungs that are already injured, this threshold is likely to be different.