Ultrasound shear wave elastography for assessing diaphragm function in mechanically ventilated patients: a breath-by-bre
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RESEARCH
Ultrasound shear wave elastography for assessing diaphragm function in mechanically ventilated patients: a breath‑by‑breath analysis Quentin Fossé1,2†, Thomas Poulard3,4†, Marie‑Cécile Niérat1, Sara Virolle1,2, Elise Morawiec1,2, Jean‑Yves Hogrel3, Thomas Similowski1,2, Alexandre Demoule1,2, Jean‑Luc Gennisson4, Damien Bachasson3† and Martin Dres1,2*†
Abstract Background: Diaphragm dysfunction is highly prevalent in mechanically ventilated patients. Recent work showed that changes in diaphragm shear modulus (ΔSMdi) assessed using ultrasound shear wave elastography (SWE) are strongly related to changes in Pdi (ΔPdi) in healthy subjects. The aims of this study were to investigate the relationship between ΔSMdi and ΔPdi in mechanically ventilated patients, and whether ΔSMdi is responsive to change in respira‑ tory load when varying the ventilator settings. Methods: A prospective, monocentric study was conducted in a 15-bed ICU. Patients were included if they met the readiness-to-wean criteria. Pdi was continuously monitored using a double-balloon feeding catheter orally intro‑ duced. The zone of apposition of the right hemidiaphragm was imaged using a linear transducer (SL10-2, Aixplorer, Supersonic Imagine, France). Ultrasound recordings were performed under various pressure support settings and dur‑ ing a spontaneous breathing trial (SBT). A breath-by-breath analysis was performed, allowing the direct comparison between ΔPdi and ΔSMdi. Pearson’s correlation coefficients (r) were used to investigate within-individual relationships between variables, and repeated measure correlations (R) were used for determining overall relationships between variables. Linear mixed models were used to compare breathing indices across the conditions of ventilation. Results: Thirty patients were included and 930 respiratory cycles were analyzed. Twenty-five were considered for the analysis. A significant correlation was found between ΔPdi and ΔSMdi (R = 0.45, 95% CIs [0.35 0.54], p 90% or PaO2/FiO2 ≥ 150 mmHg with a fraction of inspired oxygen (FiO2) ≤ 40%, no or minimal vasopressor, and a positive end-expiratory pressure (PEEP) ≤ 8 cmH2O. Patients who were pregnant, under a legal protection measure, with a contraindication to the insertion of a gastric-esophageal probe (esophageal bleeding), or with known allergies to anesthetizing were not included. Flow and pressure measurements
A flow sensor (Hamilton Medical, Bonaduz, Switzerland) connected to a spirometer (ADInstruments, Bella Vista, Australia) was used to continuously measure flow. Esophageal (Pes) and gastric (Pga) pressures were monitored using a double-balloon feeding catheter (NutriVentTM, Mirandola, Modena, Italy). The catheter was inserted through the mouth or nostril in the esophagus as demonstrated by the appearance of cardiac artifacts and appropriate negative swings of pressure during inspiration. Both balloons were inflated with 3 to 4 ml of air and connected to separated differential pressure transducers (model DP45-32, Validyne, North
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