Methodological and Clinimetric Evaluation of Inspiratory Respiratory Muscle Ultrasound in the Critical Care Setting: A Systematic Review and Meta-Analysis.

Objective: Significant variations exist in the use of respiratory muscle ultrasound in intensive care with no society-level consensus on the optimal methodology. This systematic review aims to evaluate, synthesize, and compare the clinimetric properties of different image acquisition and analysis methodologies.
Data Sources: Systematic search of five databases up to November 24, 2021.
Study Selection: Studies were included if they enrolled at least 50 adult ICU patients, reported respiratory muscle (diaphragm or intercostal) ultrasound measuring either echotexture, muscle thickness, thickening fraction, or excursion, and evaluated at least one clinimetric property. Two independent reviewers assessed titles, abstracts, and full text against eligibility.
Data Extraction: Study demographics, ultrasound methodologies, and clinimetric data.
Data Synthesis: Sixty studies, including 5,025 patients, were included with 39 studies contributing to meta-analyses. Most commonly measured was diaphragm thickness (DT) or diaphragm thickening fraction (DTF) using a linear transducer in B-mode, or diaphragm excursion (DE) using a curvilinear transducer in M-mode. There are significant variations in imaging methodology and acquisition across all studies. Inter- and intrarater measurement reliabilities were generally excellent, with the highest reliability reported for DT (ICC, 0.98; 95% CI, 0.94-0.99). Pooled data demonstrated acceptable to excellent accuracy for DT, DTF, and DE to predicting weaning outcome after 48 to 72 hours postextubation (DTF AUC, 0.79; 95% CI, 0.73-0.85). DT imaging was responsive to change over time. Only three eligible studies were available for intercostal muscles. Intercostal thickening fraction was shown to have excellent accuracy of predicting weaning outcome after 48-hour postextubation (AUC, 0.84; 95% CI, 0.78-0.91).
Conclusions: Diaphragm muscle ultrasound is reliable, valid, and responsive in ICU patients, but significant variation exists in the imaging acquisition and analysis methodologies. Future work should focus on developing standardized protocols for ultrasound imaging and consider further research into the role of intercostal muscle imaging.
Competing Interests: Dr. Parry is currently a recipient of a Val and Al Rosenstrauss Fellowship. Dr. Sarwal’s institution has received compensation for research support for conducting multicenter clinical trials from Bard, Biogen, Novartis, and CVR Global. Her institute has received compensation from LungPacer and NIH/NIA R01 AG066910-01 (Brinkley/Shaltout) for her role as a consultant for ultrasound image analysis in clinical research trial. She has received honorarium, free meeting registration, or reimbursement of travel expenses for role as speaker from Society of Critical Care Medicine, Neurocritical Society, Indian Society of Critical Care Medicine, Indian Academy of Neurology, American Institute of Ultrasound in Medicine, Intensive Care Society, American College of Chest Physicians, American Thoracic Society, and American Association of Physical Therapists. The remaining authors have disclosed that they do not have any potential conflicts of interest.
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