High Tidal Volume Variability Is Associated With Worse Outcomes in Patients With ARDS

Background: The impact of spontaneous breathing during mechanical ventilation on the outcome of ARDS has yet to be established. This study aimed to evaluate the effect of tidal volume variability on ventilator-free days in mechanically ventilated subjects with ARDS using high-resolution tidal volume data collected through patient monitors. Methods: This single-center, retrospective cohort study included adult subjects with ARDS who received mechanical ventilation in our medical ICU between April 2018 and July 2019. The study subjects' expiratory tidal volume data during the first 7 days of mechanical ventilation were collected every 2 s from the patient monitors. The subjects were divided equally into 3 groups according to the coefficient of variation (CV) of all collected normalized tidal volume values. Results: A total of 108 subjects with ARDS were categorized into the low, intermediate, and high CV groups (each number = 36). Baseline characteristics of the 3 groups were comparable except for a lower P_aO2/F_IO2 in the low CV group (130 ± 50 mm Hg vs 160 ± 57 mm Hg vs 158 ± 50 mm Hg, P = .03). On average, 222,776 tidal volume data points were collected per subject during the first 7 days of mechanical ventilation. The CVs of tidal volume were 17% ± 3%, 26% ± 2%, and 38% ± 8% in each group, respectively. The number of ventilator-free days was significantly lower in the high CV group than in the intermediate CV group (0 [interquartile range or IQR, 0-2.5] days vs 16 [IQR, 0-21.5] days, P = .004 after Bonferroni correction). After adjusting in the zero-inflated negative binomial model, high CV was significantly associated with fewer ventilator-free days compared with intermediate CV (odds ratio, 11.1, 95% CI [2.3-52.7], P = .002). Conclusions: Based on the high-resolution tidal volume data from the ventilator monitors, high tidal volume variability during the first 7 days of mechanical ventilation in subjects with ARDS was associated with fewer ventilator-free days.