• Jonne Doorduin, Lisanne H Roesthuis, Diana Jansen, Johannes G van der Hoeven, van Hees Hieronymus W H HWH, and Heunks Leo M A LMA.
• From the Departments of Critical Care Medicine (J.D., L.H.R., J.G.v.d.H., L.M.A.H.) Anesthesiology (D.J.) Pulmonary Diseases (H.W.H.v.H.) the Donders Institute for Brain, Cognition and Behaviour, Department of Neurology (J.D.) Radboud University Medical Center, Nijmegen, The Netherlands; and the Department of Intensive Care Medicine, VU University Medical Center, Amsterdam, The Netherlands (L.M.A.H.).
• Anesthesiology. 2018 Sep 1; 129 (3): 490-501.

What We Already Know About This TopicWHAT THIS ARTICLE TELLS US THAT IS NEW: BACKGROUND:: Respiratory muscle weakness in critically ill patients is associated with difficulty in weaning from mechanical ventilation. Previous studies have mainly focused on inspiratory muscle activity during weaning; expiratory muscle activity is less well understood. The current study describes expiratory muscle activity during weaning, including tonic diaphragm activity. The authors hypothesized that expiratory muscle effort is greater in patients who fail to wean compared to those who wean successfully.MethodsTwenty adult patients receiving mechanical ventilation (more than 72 h) performed a spontaneous breathing trial. Tidal volume, transdiaphragmatic pressure, diaphragm electrical activity, and diaphragm neuromechanical efficiency were calculated on a breath-by-breath basis. Inspiratory (and expiratory) muscle efforts were calculated as the inspiratory esophageal (and expiratory gastric) pressure-time products, respectively.ResultsNine patients failed weaning. The contribution of the expiratory muscles to total respiratory muscle effort increased in the "failure" group from 13 ± 9% at onset to 24 ± 10% at the end of the breathing trial (P = 0.047); there was no increase in the "success" group. Diaphragm electrical activity (expressed as the percentage of inspiratory peak) was low at end expiration (failure, 3 ± 2%; success, 4 ± 6%) and equal between groups during the entire expiratory phase (P = 0.407). Diaphragm neuromechanical efficiency was lower in the failure versus success groups (0.38 ± 0.16 vs. 0.71 ± 0.36 cm H2O/μV; P = 0.054).ConclusionsWeaning failure (vs. success) is associated with increased effort of the expiratory muscles and impaired neuromechanical efficiency of the diaphragm but no difference in tonic activity of the diaphragm.

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