Bedside Estimate of Mechanical Power (Part 4): Power Intensity Thresholds and Mortality Risk in ARDS

Abstract

Background: Mechanical power (W) is ventilator energy transferred to the respiratory system (ie, W_RS) over time (J/min). W_RS exceeding 12, 15, and 25 J/min are considered ventilator-induced lung injury (VILI) thresholds of increasing severity.¹ This study examined mortality risk associated with five W_RS thresholds.

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. A simplified W_RS calculation was used: W_RS = 0.098 x frequency x V_T x (PEEP + P_DR).² Mortality risk was assessed at W_RS thresholds of > 12, > 15, > 20 > 25, and > 30 J/min using Fisher-exact tests. Alpha was set at 0.05.

Results: Mortality steadily increased both below and above each threshold, with cumulative mortality increases 8% vs. 14% respectively: the relative increases being the same for each cohort (138%). Over 40% of cases had W_RS levels exceeding those associated with severe VILI risk.

Conclusions: Mild and severe ARDS mortality (27%, and 45% respectively)³ approximates that found between cohorts across the 25 J/min threshold (27% and 47% respectively): a threshold associated with severe ventilator-induced lung injury.¹ Given relative inexactness of the simplified clinical equation used, this particular finding only cautiously suggests a relatively high tolerance of W_RS ≤ 25 J/min.1. Silva PL et al. Anesthesiology 2020;132:949. 2. Chiumello D et al. Crit Care 2020;24:417. 3. Berlin Taskforce. JAMA 2012;307:2526.