Introduction: Mechanical ventilation is a life-saving treatment that is however associated with diaphragm dysfunction. The optimal ventilator settings providing a lung protective ventilation while maintaining a safe diaphragm activity are difficult to determine. A noninvasive and bedside evaluation of the diaphragm activity could be helpful. We investigated whether changes in diaphragm stiffness (ΔSMdi) assessed using ultrasound shear wave elastography (SWE) may be used as a surrogate of changes in transdiaphragmatic pressure (ΔPdi) in mechanically ventilated (MV) patients.Methods: Pdi was continuously monitored using esophageal and gastric balloons and SMdi was measured at the zone of apposition of the right hemi-diaphragm. Measurements were performed twice under initial ventilator settings and every five minutes during a spontaneous breathing trial (SBT). Pearson correlation coefficient (r) were used to determine within-individual and overall relationships between Pdi and SMdi.Results: Among the 25 patients enrolled, 8 displayed a significant ΔSMdi-ΔPdi correlation (r=0.62-0.88, p<0.05). Compared to others, patients with significant correlations had a lower respiratory rate (16±5 vs 24±6 breath/min, respectively; p<0.01) and a significant increase in ΔSMdi between initial ventilator settings and the SBT. Patients without ΔSMdi-ΔPdi correlation only had an increase in ΔPdi during the SBT with no concomitant increase in ΔSMdi.Conclusion: SMdi obtained by SWE appears as a promising technique to assess diaphragm activity in MV patients. Technological improvements are necessary to increase SWE sampling rate before enabling its generalization in the ICU.FootnotesCite this article as: ERJ Open Research 2020; 6: Suppl. 4, 19.This is an ERS Respiratory Failure and Mechanical Ventilation Conference abstract. No full-text version is available. Further material to accompany this abstract may be available at www.ers-education.org (ERS member access only).