Decline in Ventilatory Ratio as a Predictor of Mortality in Adults With ARDS Receiving Prone Positioning

Respir Care. 2022 Aug 24;67(9):1067-1074. doi: 10.4187/respcare.09783.

Abstract

Background: Prone positioning reduces mortality in patients with moderate/severe ARDS. It remains unclear which physiological parameters could guide clinicians to assess which patients are likely to benefit from prone position. This study aimed to determine the association between relative changes in physiological parameters at 24 h of prone positioning and ICU mortality in adult subjects with ARDS.

Methods: We conducted a cohort study using the VENTILA database, including adults with ARDS receiving prone positioning. We used multivariable logistic regression to assess the association between relative changes in physiological parameters (PaO2 /FIO2 , dynamic driving pressure, PaCO2 , and ventilatory ratio defined as [minute ventilation [mL/min] × PaCO2 [mm Hg]]/[predicted body weight × 100 [mL/min] × 37.5 [mm Hg] with ICU mortality) (primary outcome). We report adjusted odds ratios with 95% CI as measures of association.

Results: We included 156 subjects of which 82 (53%) died in the ICU. A relative decline in the ventilatory ratio at 24 h was associated with lower ICU mortality (odds ratio 0.80 [95% CI 0.66-0.97], every 10% decrease). Relative changes in PaO2 /FIO2 (odds ratio 0.89 [95% CI 0.77-1.03], every 25% increase), PaCO2 (odds ratio 0.97 [95% CI 0.82-1.16], every 10% decrease), and dynamic driving pressure (odds ratio 0.98 [95% CI 0.89-1.07], every 10% decrease) were not associated with ICU mortality.

Conclusions: In subjects with ARDS receiving prone positioning, a relative decline in the ventilatory ratio at 24 h was associated with lower ICU mortality.

Keywords: ARDS; prone position; respiratory dead space; ventilatory ratio.