Pressure Control Surrogate Formula for Estimating Mechanical Power in ARDS is Associated with Mortality.

ABSTRACT

BACKGROUND: Mechanical power applied to the respiratory system (MPRS) is associated with ventilator-induced lung injury (VILI) and ARDS mortality. Absent automated ventilator MPRS 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 ARDS subjects managed almost exclusively with volume-control ventilation.METHODS: 948 subjects were studied in whom invasive mechanical ventilation and implementation of ARDSNet ventilator protocols commenced ≤ 24hr after ARDS onset, and who survived > 24hr. MPRS was calculated as 0.098 x respiratory frequency x VT x (PEEP + driving pressure [PDR]). MPRS 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 MPRS thresholds associated with VILI or mortality (ie. 15, 20, 25 and 30 J/m).RESULTS: MPRS was associated with increased mortality risk Odds Ratio (95% CI) of 1.06 (1.04-1.07) per J/m, P<0.001). Median MPRS differentiated non-survivors from survivors in Mild (24.7 vs. 18.5 J/m, respectively, P==0.034); Moderate (25.7 vs. 21.3 J/m, P<0.001); and Severe ARDS (28.7 vs. 23.5 J/m, P<0.001). Across 4 MPRS thresholds mortality increased from 23-29% when MPRS was < threshold vs. 38-51% when MPRS was > threshold (P<0.001). 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 volume control ventilation. In our subjects when MPRS exceeds established cut-off values for VILI or mortality risk, we found mortality risk consistently increased by a factor of > 2.0.