Abstract
BACKGROUND: Ventilator-induced lung injury (VILI) requires repetitive transfer of energy from the ventilator to the compromised lung. To understand this phenomenon, 2 sets of equations have been developed to partition total inflation energy into harmless and hazardous components using an arbitrary level of alveolar pressure as a threshold beyond which further energy increments may become damaging. One set of equations uses premeasured resistance and compliance as inputs to predict the energy that would be delivered by typical ventilator settings, whereas the other equation set uses observed output values for end-inspiratory peak and plateau pressure of an already completed inflation. METHODS: Our aim for this study was to compare the relative accuracy of these equation sets against the performance of a physical one-compartment model of the respiratory system, programmed with information readily available at the bedside and ventilated using both constant and decelerating flow profiles. Accordingly, equations of each set were compared against the corresponding energy areas measured by digital planimetry of pressure-volume curves for 76 ventilator and patient parameter combinations and over 500 power calculations. RESULTS: With few exceptions, all equations strongly correlated with their corresponding measurements by planimetry. CONCLUSIONS: This validation of threshold-partitioned energy equations suggests their potential utility for implementing practical strategies for VILI avoidance.