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

BACKGROUND

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 (VTe/PBW), a surrogate of lung-distending pressure.

METHODS

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 VTe recorded during an early positive pressure session using an oronasal mask and a double-limb circuit. VTe/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 VTe/PBW cutoff associated with unfavorable outcome was identified with the Youden index. Univariate and multivariate analyses were performed.

RESULTS

Eighty subjects were included, 38 (47.5%) with unfavorable outcome. Median VTe/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, VTe/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, SpO2/FiO2 ratio at admission, and VOX index. The area under the receiver operating characteristic curve for the correlation between VTe/PBW and unfavorable outcome was 0.66. Based on the Youden index, the VTe/PBW cutoff most strongly associated with the outcome was 8.5 mL/kg PBW. Nevertheless, because differences across VTe/PBW cutoffs were small, this threshold should be considered hypothesis-generating.

CONCLUSIONS

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