Critical Care Medicine

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Critical Care Medicine:
doi: 10.1097/CCM.0b013e31827caba0
Clinical Investigations

Estimation of Patient’s Inspiratory Effort From the Electrical Activity of the Diaphragm*

Bellani, Giacomo MD, PhD1,2; Mauri, Tommaso MD1,2; Coppadoro, Andrea MD1,2; Grasselli, Giacomo MD2; Patroniti, Nicolò MD1,2; Spadaro, Savino MD2; Sala, Vittoria MD1,2; Foti, Giuseppe MD2; Pesenti, Antonio MD1,2

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Objectives: To calculate an index (termed Pmusc/Eadi index) relating the pressure generated by the respiratory muscles (Pmusc) to the electrical activity of the diaphragm (Eadi), during assisted mechanical ventilation and to assess if the Pmusc/Eadi index is affected by the type and level of ventilator assistance. The Pmusc/Eadi index was also used to measure the patient’s inspiratory effort from Eadi without esophageal pressure.

Design: Crossover study.

Setting: One general ICU.

Patients: Ten patients undergoing assisted ventilation.

Intervention: Pressure support and neurally adjusted ventilator assist delivered, each, at three levels of ventilatory assistance.

Measurement and Main Results: Airways flow and pressure, esophageal pressure, and Eadi were continuously recorded. Sixty tidal volumes for each ventilator settings were analyzed off-line, at three time points during inspiration. For each time point, Pmusc/Eadi index was calculated. Pmusc/Eadi index was also calculated from airway pressure drop during end-expiratory occlusions. Pmusc/Eadi index was very variable among patients, but within one patient it was not affected by type and level of ventilator assistance. Pmusc/Eadi index decreased during the inspiration. Pmusc/Eadi index obtained during an occlusion from airway pressure swing was tightly correlated with that derived from esophageal pressure during tidal ventilation and allowed to estimate pressure time product.

Conclusions: Pmusc is tightly related to Eadi, by a proportionality coefficient that we termed Pmusc/Eadi index, stable within each patient under different conditions of ventilator assistance. The derivation of the Pmusc/Eadi index from Eadi and airway pressure during an expiratory occlusion enables a continuous estimate of patient’s inspiratory effort.

© 2013 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins

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