Comparison of Airway-Based and Transpulmonary Mechanical Power Across Ventilation Conditions in Moderate-to-Severe...

Background: Mechanical ventilation is essential for managing acute respiratory distress syndrome (ARDS) but may contribute to ventilator-induced lung injury (VILI). Mechanical power (MP), an integrative measure combining tidal volume, respiratory rate, and airway pressures, has emerged as a predictor of VILI. However, conventional MP calculations based on airway driving pressure (ΔP) reflect the mechanical load applied to the entire respiratory system, including both lung parenchyma and chest wall. Estimation of transpulmonary pressure using esophageal pressure allows calculation of transpulmonary mechanical power (TPMP), which may more accurately represent lung stress. Methods: We conducted a retrospective observational study of 20 mechanically ventilated ICU patients with available esophageal pressure measurements at Wolfson Medical Center between 2012 and 2015. MP and TPMP were calculated across ventilation modes, including continuous mandatory ventilation assist/control (CMV/AC), synchronized intermittent mandatory ventilation (SIMV), and continuous positive airway pressure/pressure support ventilation (CPAP/PSV). Paired comparisons were analyzed using the Wilcoxon signed-rank test; repeated-measures Friedman tests were used to assess within-patient differences in MP, TPMP, and the MP-TPMP difference across the four ventilation conditions. Results: At baseline, MP and TPMP values were similar, with only a small absolute difference despite statistical significance (median 20 vs. 20 J/min; p = 0.0107). Differences were more pronounced and mode-dependent during CMV/AC, CPAP/PSV, and SIMV. During CMV/AC, TPMP exceeded MP (median 23 vs. 22 J/min; p = 0.0016). In contrast, TPMP was lower than MP during CPAP/PSV (median 14 vs. 20 J/min; p < 0.0001) and SIMV (median 17 vs. 23 J/min; p = 0.0073). In a repeated-measures analysis, the within-patient MP-TPMP difference varied significantly across ventilation conditions (χ² = 33.06, df = 3, p < 0.0001), while MP alone did not differ significantly across conditions (χ² = 6.90, df = 3, p = 0.075); these findings represent associations with ventilation condition and clinical state rather than a causal effect of ventilation mode. Conclusions: This exploratory study demonstrates that airway-based MP and esophageal pressure-derived TPMP provide different estimates of mechanical load and that the magnitude and direction of these differences vary across ventilation conditions. These findings support the physiological relevance of considering transpulmonary pressure when characterizing respiratory mechanical load. However, this study does not establish that TPMP-guided ventilation improves clinical outcomes or reduces VILI. The potential clinical value of TPMP should therefore be evaluated in larger prospective studies.