• Aurelien Flatres, Yassir Aarab, Stephanie Nougaret, Fanny Garnier, Romaric Larcher, Mathieu Amalric, Kada Klouche, Pascal Etienne, Gilles Subra, Samir Jaber, Nicolas Molinari, Stefan Matecki, and Boris Jung.
• Medical Intensive Care Unit, Montpellier University and Montpellier Lapeyronie Teaching Hospital, Avenue du Doyen Gaston Giraud, 34000, Montpellier, France.
• Crit Care. 2020 Feb 3; 24 (1): 34.

BackgroundMuscle weakness following critical illness is the consequence of loss of muscle mass and alteration of muscle quality. It is associated with long-term disability. Ultrasonography is a reliable tool to quantify muscle mass, but studies that evaluate muscle quality at the critically ill bedside are lacking. Shear wave ultrasound elastography (SWE) provides spatial representation of soft tissue stiffness and measures of muscle quality. The reliability and reproducibility of SWE in critically ill patients has never been evaluated.MethodsTwo operators tested in healthy controls and in critically ill patients the intra- and inter-operator reliability of the SWE using transversal and longitudinal views of the diaphragm and limb muscles. Reliability was calculated using the intra-class correlation coefficient and a bootstrap sampling method assessed their consistency.ResultsWe collected 560 images. Longitudinal views of the diaphragm (ICC 0.83 [0.50-0.94]), the biceps brachii (ICC 0.88 [0.67-0.96]) and the rectus femoris (ICC 0.76 [0.34-0.91]) were the most reliable views in a training set of healthy controls. Intra-class correlation coefficient for inter-operator reproducibility and intra-operator reliability was above 0.9 for all muscles in a validation set of healthy controls. In critically ill patients, inter-operator reproducibility and intra-operator 1 and 2 reliability ICCs were respectively 0.92 [0.71-0.98], 0.93 [0.82-0.98] and 0.92 [0.81-0.98] for the diaphragm; 0.96 [0.86-0.99], 0.98 [0.94-0.99] and 0.99 [0.96-1] for the biceps brachii and 0.91 [0.51-0.98], 0.97 [0.93-0.99] and 0.99 [0.97-1] for the rectus femoris. The probability to reach intra-class correlation coefficient greater than 0.8 in a 10,000 bootstrap sampling for inter-operator reproducibility was respectively 81%, 84% and 78% for the diaphragm, the biceps brachii and the rectus femoris respectively.ConclusionsSWE is a reliable technique to evaluate limb muscles and the diaphragm in both healthy controls and in critically ill patients.Trial RegistrationThe study was registered (ClinicalTrial NCT03550222).

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