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.
1 Department of Experimental Medicine, University of Milan-Bicocca, Monza, Italy.
2 Department of Emergency and Intensive Care, San Gerardo Hospital, Monza, Italy.
*See also p. 1584.
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Drs. Grasselli and Pesenti received support for travel from Maquet. Dr. Pesenti received support for travel from Draeger and Lilly.
Drs. Bellani and Pesenti received grant support from Chiesi Farmaceutica SPA, Maquet, and Draeger. Dr. Patroniti received funding from Milano Bicocca University.
Dr. Bellani has board membership with GE Healthcare. Dr. Grasselli has patents with St Michael's Hospital-Toronto. Dr. Foti lectured for Maquet. Dr. Pesenti consulted for Bellco.
The remaining authors have disclosed that they do not have any potential conflicts of interest.
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