Bedside Estimate of Mechanical Power (Part 1): Mortality Risk in ARDS Comparing Power Applied to the Respiratory System and Its Lung and Chest Wall Components

Background: Mechanical power (W) represents ventilator energy transferred to the lungs and chest wall (ie, WRS) over time. WRS is linked to both ventilator-induced lung injury and ARDS mortality. Estimating WRS is complex and unwieldy as it encompasses minute ventilation, peak airway pressure, PEEP, and inspiratory flow.1 A simplified, clinical equation for pressure control ventilation (PCV): WRS = 0.098 x frequency x VT x (PEEP + PDR),1 was used in this retrospective study to assess mortality risk, without distinguishing CMV modes (ie, PDR = Pplat-PEEP vs. PIP-PEEP, and excluding inspiratory flow). Methods: 948 ARDS subjects were studied who: 1) met the Berlin definition, 2) were managed with ARDSNet protocols initiated ≤ 24 h after ARDS onset, and 3) survived ≥ 24 h after protocol initiation (allowing lung-protective ventilation optimization and censoring moribund cases). WL and WCW were estimated using subcomponents of ARDS elastance data:2 EL/ERS (0.72), ECW:/ERS (0.28). Other calculations included ratio of measured WRS to normal WRS (∼4 J/min) and ΔWRS ∼24 h after protocol initiation. Mortality risk was assessed by univariate logistic regression. Alpha was set at 0.05. Results: Hospital mortality was 35.6%. All W estimates predicted mortality risk (Table), having identical area under the receiver operating curve and P-values: AUC (95%CI) 0.65 (0.61-0.69), P < .001. WRS was ∼ 6-fold higher than normal: median (IQR) 5.8 (4.4-7.8). WCW, was associated with a higher mortality risk than WL. Conclusions: A simplified WRS estimate of ARDS mortality risk suggests complex W equations may not be clinically necessary. Higher mortality risk with increasing WCW might reflect the presence of intra-abdominal hypertension that may portend worse clinical outcomes in ARDS. 1. Chiumello D et al. Crit Care 2020;24:417. 2. Kallet RH et al. Respir Care 2007;52(8):989. Odds Ratio (95% CI)Wrs1.06 (1.04-1.07)WL1.08 (1.06-1.10)Wcw1.23 (1.17-1.29)W Ratio1.25 (1.18-1.32)ΔWrs1.02 (1.01-1.04)