Mechanical Power Indexed to Estimated Functional Residual Capacity as a Predictor of Mortality in Acute Respiratory Distress Syndrome: Post Hoc Analysis.

BACKGROUND AND AIMS: Mechanical power (MP) reflects the energy delivered by the ventilator and has been associated with mortality in acute respiratory distress syndrome (ARDS). We evaluated whether MP indexed to estimated functional residual capacity (MP/FRC) was associated with intensive care unit (ICU) mortality in ARDS. PATIENTS AND METHODS: This post hoc analysis included 158 adult patients with ARDS who required invasive mechanical ventilation between 2016 and 2022. Functional residual capacity was physiologically estimated from standard ventilatory variables. Mechanical power, MP/FRC, dynamic strain, and global strain were calculated. The primary outcome was ICU mortality. Discrimination was evaluated using receiver operating characteristic (ROC) analysis, and survival was assessed using Cox regression. RESULTS: Eighty-one patients (51%) died during ICU stay. Mechanical power/FRC demonstrated the highest observed discrimination for ICU mortality among the evaluated respiratory indices [area under the curve (AUC) 0.71; 95% CI 0.62-0.81]. A cutoff value of 33.94 J/min/L was associated with significantly lower ICU survival (log-rank p < 0.001). Mechanical power/FRC remained independently associated with ICU mortality in multivariable analysis [hazard ratio (HR) 1.06 per unit increase; p = 0.005]. CONCLUSION: Mechanical power/FRC was independently associated with ICU mortality and showed the highest observed discriminative performance among the evaluated respiratory indices. Because FRC was estimated rather than directly measured, these findings should be considered hypothesis-generating and require prospective validation.