Bedside Estimate of Mechanical Power (Part 5): Mortality Risk in ARDS Comparing Predictive Thresholds for Plateau Pressure,Driving Pressure,and Mechanical Power

Abstract

Background:

Previous abstract (Part 4) compared mechanical power transferred to the respiratory system (W_RS), in which below/above the 20 J/min threshold revealed a widening mortality departure (ie, 24% vs. 42% respectively). Those whose W_RS > 20 J/min accounted for 65% of subjects. Thresholds in plateau pressure (Pplat) > 30 cm H₂O and driving pressure (P_DR) > 15 cm H₂O are also associated with increasing mortality risk in ARDS.^1,2 This study examined the relevance of all three thresholds on mortality risk when compared to prominent non-pulmonary factors that drive mortality in ARDS.³

Methods:

948 ARDS subjects previously described (abstracts part 1-4) had threshold values for W_RS, Pplat and P_DR compared to non-pulmonary factors (ie, age, ARDSNet study comorbidity exclusion criteria,¹ and APACHE II scores) both in univariate and multivariate logistic regression modeling. Alpha was set at 0.05.

Results:

In univariate analyses all variables were associated with mortality risk (P < .001). Low collinearity was found between dichotomous expressions of the inter-related variables W_RS, Pplat and P_DR (R²:0.19, 0.19, 0.23 respectively). Multivariate modelling revealed Pplat and W_RS thresholds, but not P_DR threshold, remained strongly associated with mortality when controlled for non-pulmonary variables (Table). Area under receiver operative curve of 0.80 (95%CI: 0.77-0.83), P < .001.

Conclusions:

When lung protective ventilation is initiated ≤ 24 h after ARDS onset, exceeding Pplat and W_RS thresholds influences mortality rather than P_DR threshold > 15 cm H₂O.1. ARDS Network. N Engl J Med 2000;342(18):1301. 2. Amato MB et al. N Engl J Med 2015;372(8):747. Kallet RH et al. Respir Care 2019;64(5):493.

Table 1

Variables	Odds Ratio (95%CI)	P
Age	1.03 (1.02-1.04)	<0.001
ARDSNet Exclusion+	2.52 (1.83-3.47)	<0.001
APACHE II*	1.09 (1.06-1.11)	<0.001
Wrs > 20 J/m	1.76 (1.22-2.56)	0.003
Pplat > 30 cmH2O	3.16 (1.92-5.25)	<0.001
Pdr > 15 cmH2O	1.23 (0.86-1.76)	0.25

*APACHE = acute physiology and chronic health evaluation

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