Mechanical power (MP), defined as the total mechanical energy delivered during the inflation phase of the tidal cycle multiplied by the breathing frequency (f), is a composite variable encompassing both static and dynamic respiratory parameters. In preclinical studies of lung injury analogous to ARDS, ventilator-induced lung injury (VILI) has been more closely attributed to a combination of MP components rather than to any single component individually.
However, clinical studies have found that among the components of MP, driving pressure ( ΔP), or ΔP combined with f, are most closely associated with mortality. We emphasize here that VILI has been assumed to be, but has not been directly shown in the clinical setting, the key driver of those associations. In that context of VILI, however, it is important to understand that mechanical ventilation differentially affects open airspaces; for this reason, mechanical energy needed to adequately ventilate transfers to a smaller functional lung, often referred to as the “baby lung”. In the setting of acute lung injury, the size of the functional lung is the primary determinant of respiratory-system compliance (CRS). Because inflation energy delivered to individual lung units generates tissue strain and potential VILI risk, MP normalized to CRS (MP/CRS) could be an important parameter to evaluate, especially considering the heightened vulnerability of this heterogeneous and stress-focused mechanical environment of ARDS. Indeed, previous studies have identified an association between MP/CRS and mortality. However, it remains unclear which specific MP components are most strongly linked to MP/CRS. Understanding which MP components may be associated with MP/CRS could help refine ventilatory settings, as it would allow for better targeted adjustments aimed at reducing VILI.
The objectives of this physiological study were to identify variables that significantly differed based on an MP/CRS threshold for mortality and, among the MP components showing significant differences, to determine which were most closely associated with MP/CRS.