Tidal Volume Threshold for Noninvasive Respiratory Support Failure in Hypoxemic Respiratory Failure

Identifying predictors of noninvasive respiratory support failure is crucial to avoid delays in intubation. This study assessed, in a homogeneous group of patients with SARS-CoV-2-related acute hypoxemic respiratory failure (AHRF), the association between outcome and early measured expired tidal volume normalized to predicted body weight (V_Te/PBW), a surrogate of lung-distending pressure.

This single-center retrospective study was conducted at a Swiss tertiary-care university hospital. Data were collected from medical records of patients admitted to the ICU between March 2020 and April 2022 for SARS-CoV-2-related AHRF requiring noninvasive respiratory support, with V_Te recorded during an early positive pressure session using an oronasal mask and a double-limb circuit. V_Te/PBW and other potential factors associated with outcome were compared between patients with favorable and unfavorable (intubation and/or ICU death) outcomes using Fisher's exact and Mann-Whitney tests. The optimal V_Te/PBW cutoff associated with unfavorable outcome was identified with the Youden index. Univariate and multivariate analyses were performed.

Eighty subjects were included, 38 (47.5%) with unfavorable outcome. Median V_Te/PBW was higher in the unfavorable outcome group (9.8 [8.6-11.5] vs 8.5 [7.6-10.1] mL/kg PBW, P = .02). In univariate analysis, V_Te/PBW was associated with outcome (odds ratio [OR] = 1.27, 95% CI = 1.06-1.57), as were age, gender, Sequential Organ Failure Assessment, SAPS II, $S_{{\mathrm{pO}}_2}$/$F_{{\mathrm{iO}}_2}$ ratio at admission, and VOX index. The area under the receiver operating characteristic curve for the correlation between V_Te/PBW and unfavorable outcome was 0.66. Based on the Youden index, the V_Te/PBW cutoff most strongly associated with the outcome was 8.5 mL/kg PBW. Nevertheless, because differences across V_Te/PBW cutoffs were small, this threshold should be considered hypothesis-generating.

V_Te/PBW during an early positive-pressure ventilation session was associated with worsening outcomes in subjects with SARS-CoV-2-related AHRF. The V_Te/PBW cutoff most strongly associated with unfavorable outcome was 8.5 mL/kg PBW.