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BACKGROUND: Quantification of patient effort during spontaneous breathing is important to tailor ventilatory assistance. Because a correlation between inspiratory muscle pressure (Pmus) and electrical activity of the diaphragm (EAdi) has been described, we aimed to assess the reliability of surface electromyography (EMG) of the respiratory muscles for monitoring diaphragm electrical activity and subject effort during assisted ventilation. METHODS: At a general ICU of a single university-affiliated hospital, we enrolled subjects who were intubated and on pressure support ventilation (PSV) and were on mechanical ventilation for > 48 h. The subjects were studied at 3 levels of pressure support. Airway flow and pressure; esophageal pressure; EAdi; and surface EMG of the diaphragm (surface EAdi), intercostal, and sternocleidomastoid muscles were recorded. Respiratory cycles were sampled for off-line analysis. The Pmus/EAdi index (PEI) was calculated by relying on EAdi and surface EAdi (surface PEI) from an airway pressure drop during end-expiratory occlusions performed every minute. RESULTS: surface EAdi well correlated with EAdi and Pmus, in particular, after averaging breaths into deciles (R = 0.92 and R = 0.84). When surface PEI was used with surface EAdi, it provided a reliable estimation of Pmus (R = 0.94 in comparison with measured Pmus). CONCLUSIONS: During assisted mechanical ventilation, EAdi can be reliably monitored by both EAdi and surface EMG. The measurement of Pmus based on the calibration of EAdi was also feasible by the use of surface EMG. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]