Brower RG, Lanken PN, MacIntyre N, et al. Higher versus lower positive end-expiratory pressures in patients with the acute respiratory distress syndrome.

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Concerning inter-visit repeatability, the data from 56 subjects with CF (adult and children) exhibited stability across the two measurements, with no significant difference between LCI measurements (paired t test, P ¼ .80). 1 The mean %CV for visit 1 (4.3%) and visit 2 (4.7%) were also not significantly different (paired t test, P ¼ .21). These results were comparable to the intra-visit %CV reported in the larger cohort of adults and children with CF. Figure 2 presents the limits of agreement between visits, which equates to a CoR of 1.4. These data underline our findings that LCI has good short-and long-term repeatability in CF but highlights that variability is greater in disease compared with health. These results emphasize that sample size estimates should be informed by CF data (and not by HC data) to avoid study underpowering. In our study, variability was comparable in children and adults with CF in contrast to some evidence that shows increased variation with disease severity and/or age. 3,4 Using %CV, CoR, and Bland-Altman statistics to assess inter-visit repeatbility, our combined child and adult CF data across 2 stable visits show levels of variation similar to those reported in the intra-visit data. We hope that this additional analysis can provide further insight into the natural variability of LCI across the age range in CF and help inform the question of what is a clinically meaningful change in LCI.