Bedside Estimate of Mechanical Power (Part 3): Power Intensity and Mortality Across Berlin Definitions of ARDS Severity

Background:

Mechanical power (W) is ventilator energy transferred to the respiratory system (ie, W_RS) over time (J/min). W_RS > 12 J/min and > 25 J/min are associated with ventilator-induced lung injury (VILI) onset and severe VILI respectively.¹ Yet, baseline W_RS of ∼ 28 J/min previously was not found to differentiate ARDS survivors from non-survivors.² This retrospective study examined whether increasing W_RS and W_L intensity corresponds with increasing mortality as ARDS intensity worsens.

Methods:

948 ARDS subjects were studied who: 1) met the Berlin definition, 2) were managed with ARDSNet protocols initiated ≤ 24 h after ARDS onset, 3) survived ≥ 24 h after protocol initiation. A simplified W_RS calculation (0.098 x frequency x V_T x [PEEP + P_DR]),² was used wherein W_L was estimated using fractional subcomponents respiratory system elastance: E_L/E_RS (0.72).³ Data were analyzed using the Mann-Whitney test. Alpha was set at 0.05.

Results:

Within ∼36-48 h of ARDS onset, significantly higher W_RS and W_L were observed in non-survivors with median W_RS approximating levels associated with severe VILI (ie, ∼25 J/min). Hospital mortality rates were similar to Berlin Taskforce findings (ie, 27%, 32%, and 45%).⁴ Lower estimates of W_L also reached the threshold wherein some degree of VILI appeared likely.

Conclusions:

Contrary to previous findings,² W_RS ∼25 J/min was associated with increased mortality risk and, by extension, perhaps severe VILI risk.1. Silva PL et al. Anesthesiology 2020;132:949. 2. Wu H-P et al. Diagnostics 2023;13:1226. 3. Kallet RH et al. Respir Care 2007; 52(8):989. 4. Berlin Taskforce. JAMA 2012; 307:2526.

Table 1

*data presented as median (IQR),† P=0.034, ‡ P<0.001, ‖ P=0.004

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