Abstract
BackgroundAlthough low tidal volume is strongly recommended for acute respiratory distress syndrome (ARDS), whether or not the benefit varies according to the severity of ARDS remains unclear. This study aimed to investigate whether or not there is an interaction between low tidal volume and severity of ARDS.MethodsThis was a secondary analysis from a randomized controlled trial. The patients were subgrouped according to whether the PaO2/FiO2 (P/F) was > 150 or ≤ 150 mmHg on day 0. The interaction between a tidal volume of 6 mL/kg and the P/F was investigated in hierarchical chi-square analysis and logistic regression models.ResultsEight hundred and thirty-six patients with ARDS were enrolled (345 in the high P/F subgroup [> 150 mmHg] and 491 in the low P/F subgroup [≤ 150 mmHg]). Compared to the traditional tidal volume group, the mortality of patients with low tidal volume was significantly lower in the high P/F subgroup (41/183 (22.4%) vs. 64/162 (39.5%), p = 0.001) but not in the low P/F subgroup (95/256 (37.1%) vs. 96/235 (40.8%), p = 0.414). In the hierarchical chi-square analysis, the test of homogeneity was significant (risk ratio of mortality 0.56 [0.40–0.79] vs. 0.91 [0.73–1.13], p = 0.018). In the multivariable logistic model, the odds ratio of mortality for the interacted item was significant (2.02, 95% confidence interval [CI] 1.06–3.86, p = 0.033). The odds ratio of mortality for low tidal volume was significant in the high P/F subgroup (0.42, 95% CI 0.24–0.72, p = 0.002) but not in the low P/F subgroup (0.89, 95% CI 0.60–1.31, p = 0.554).ConclusionsThe benefits of low tidal volume ventilation remain uncertain in patients with severe ARDS. Further studies are needed to validate this significant interaction.
Highlights
Low tidal volume is strongly recommended for acute respiratory distress syndrome (ARDS), whether or not the benefit varies according to the severity of ARDS remains unclear
We noticed in the Randomized controlled trial (RCT) reporting a negative effect of a low tidal volume ventilation strategy in ARDS [6, 7] that the baseline PaO2/FiO2 (P/F) value was significantly lower in the low tidal volume group (150 vs. 129 in the study by Brower et al [6] and 145 vs. 123 in the study by Stewart et al [7])
Given that the aim of the study was to investigate the interaction between P/F and low tidal volume ventilation in ARDS, two versions of the P/F value at different time points were used for robustness, i.e., the P/F at the time of screening, which was recorded at the time of screening in ICUs with mechanical ventilation and settings selected by clinicians, and on day 0 of the original trial which was recorded on the first day of the original trial with protocolized ventilator settings
Summary
Low tidal volume is strongly recommended for acute respiratory distress syndrome (ARDS), whether or not the benefit varies according to the severity of ARDS remains unclear. Shen et al Critical Care (2019) 23:254 and lungs with larger collapsed areas were more prone to VILI despite a tidal volume limitation of 6 mL/kg PBW than those who had lungs with smaller areas of collapse, which was partly caused by an uneven distribution of tidal volume because the normal alveoli are more prone to distention than those that are collapsed This raised the important but uninvestigated question of how much benefit patients with severe ARDS can derive from a tidal volume ventilation of 6 mL/kg PBW. We noticed in the RCTs reporting a negative effect of a low tidal volume ventilation strategy in ARDS [6, 7] that the baseline PaO2/FiO2 (P/F) value was significantly lower in the low tidal volume group (150 vs 129 in the study by Brower et al [6] and 145 vs 123 in the study by Stewart et al [7]) The reason underlying these inconsistent results remains unclear.
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