The ratio of inspiratory pressure over electrical activity of the diaphragm remains stable during icu stay and is not related to clinical outcome

BACKGROUND: We previously described an index, defined as the ratio between the inspiratory muscle pressure (Pmus) and the electrical activity of the diaphragm (EAdi) (Pmus/EAdi index). In the present work, we describe the trend of Pmus/EAdi index over time, investigating whether it could be an indicator of muscular efficiency associated with risk factors for diaphragmatic injury and/or clinical outcomes. METHODS: This work is a retrospective analysis of subjects with measurements of Pmus/EAdi index obtained, on different days, during assisted ventilation. Effects of Pmus/EAdi index absolute value on clinical outcomes were investigated dividing subjects into those with Pmus/EAdi index higher or lower than the median. Effects of Pmus/EAdi index trend over time were analyzed, distinguishing between subjects with Pmus/EAdi index increasing or decreasing. RESULTS: Mean Pmus/EAdi index was 1.04 ± 0.67, and the median (interquartile range) was 1.00 (0.59 –1.34), without a systematic trend over the days. Demographic, ventilator, or outcome data did not significantly differ between subjects with Pmus/EAdi index higher or lower than the median. Similarly, we did not find relevant differences in subjects with Pmus/EAdi index increasing or decreasing over time. CONCLUSIONS: The Pmus/EAdi index value remained constant in each subject over time, although the inter-individual variability was high. Neither the Pmus/EAdi index nor its trends appeared to be associated with ventilatory variables or clinical outcome.