The repeated transmission of energy from the ventilator to the damaged lung was required for ventilation-induced lung injury (VILI). To further explain this phenomenon, 2 sets of equations were constructed to divide total inflation energy into innocuous and hazardous components, utilizing an assumed amount of alveolar pressure as a threshold beyond which further energy increments could be harmful. About one set of equations uses premeasured resistance and compliance as inputs to anticipate the amount of energy delivered by typical ventilator settings. In contrast, the second set of equations uses observed output values for end-inspiratory peak and plateau pressure of a previously completed inflation. For a study, the researchers evaluated the relative accuracy of these equation sets to the efficiency of a real 1-compartment respiratory system model that was coded using information easily obtainable at the bedside and ventilated using both constant and decelerating flow profiles. For 76 ventilator and patient parameter combinations and over 500 power computations, the equations of each set were compared to the corresponding energy regions determined by digital planimetry of pressure-volume curves. With a few exceptions, all equations significantly correlated with planimetry results. The fact that threshold-partitioned energy equations have been validated suggested that they could be helpful in creating realistic VILI avoidance techniques.


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