Predicting Ventilator-Induced Lung Injury Using a Lung Injury Cost Function

Managing patients with acute respiratory distress syndrome (ARDS) requires mechanical ventilation that balances the competing goals of sustaining life whilst avoiding ventilator-induced lung injury (VILI). In particular, it is reasonable to suppose that, for any given ARDS patient, there must exist an optimum pair of values for tidal volume (V_T) and positive end-expiratory pressure (PEEP) that together minimize the risk for VILI. In order to find these optimum values, and thus develop a personalized approach to mechanical ventilation in ARDS, we need to be able to predict how injurious a given ventilation regimen will be in any given patient so that the minimally injurious regimen for that patient can be determined. Our goal in the present study was therefore to develop a simple computational model of the mechanical behavior of the injured lung in order to calculate potential injury cost functions to serve as predictors of VILI. We set the model parameters to represent normal, mildly injured, and severely injured lungs and estimated the amount of volutrauma and atelectrauma caused by ventilating these lungs with a range of V_T and PEEP. We estimated total VILI in two ways: 1) as the sum of the contributions from volutrauma and atelectrauma and 2) as the product of their contributions. We found the product provided estimates of VILI that are more in line with our previous experimental findings. This model may thus serve as the basis for the objective choice of mechanical ventilation parameters for the injured lung.

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