Pressure Control Surrogate Formula for Estimating Mechanical Power in ARDS Is Associated With Mortality

Background: Mechanical power (MP) applied to the respiratory system (MP_RS) is associated with ventilator-induced lung injury (VILI) and ARDS mortality. Absent automated ventilator MP_RS measurements, the alternative is clinically unwieldy equations. However, simplified surrogate formulas are now available and accurately reflect values produced by airway pressure-volume curves. This retrospective, observational study examined whether the surrogate pressure -control equation alone could accurately assess mortality risk in subjects with ARDS managed almost exclusively with volume control (VC) ventilation. Methods: Nine hundred and forty-eight subjects were studied in whom invasive mechanical ventilation and implementation of ARDS Network ventilator protocols commenced ≤ 24 h after ARDS onset and who survived > 24 h. MP_RS was calculated as 0.098 x breathing frequency x tidal volume x (PEEP + driving pressure). MP_RS was assessed as a risk factor for hospital mortality and compared between non-survivors and survivors across Berlin definition classifications. In addition, mortality was compared across 4 MP_RS thresholds associated with VILI or mortality (ie, 15, 20, 25, and 30 J/min). Results: MP_RS was associated with increased mortality risk: odds ratio (95% CI) of 1.06 (1.04-1.07) J/min (P < .001). Median MP_RS differentiated non-survivors from survivors in mild (24.7 J/min vs 18.5 J/min, respectively, P = .034), moderate (25.7 J/min vs 21.3 J/min, respectively, P < .001), and severe ARDS (28.7 J/min vs 23.5 J/min, respectively, P < .001). Across 4 MP_RS thresholds, mortality increased from 23-29% when MP_RS was ≤ threshold versus 38-51% when MP_RS was > threshold (P < .001). In the > cohort, the odds ratio (95% CI) increased from 2.03 (1.34-3.12) to 2.51 (1.87-3.33). Conclusion: The pressure control surrogate formula is sufficiently accurate to assess mortality in ARDS, even when using VC ventilation. In our subjects when MP_RS exceeds established cutoff values for VILI or mortality risk, we found mortality risk consistently increased by a factor of > 2.0.