Ultrasound method of the USVALID study to measure subcutaneous adipose tissue and muscle thickness on the thigh and upper arm: An illustrated step-by-step guide

Abstract

Summary Objective So far there is no standardised widely accepted ultrasound method for assessment of both subcutaneous adipose tissue and muscle mass in healthy subjects, patients and ICU patients. The goal is to provide an illustrated step-by-step guide of the ultrasound method developed since 2011, refined and applied during the USVALID study. Methods We use 2 linear probes with a footprint width of 25,6 and 38,4 mm. The subject is lying relaxed with the head of bed elevated to 30°. Foam supports are placed under elbows and knees. Precise anatomical landmarks are palpated to measure the limb lengths. 3 measuring points at 50% of the thigh length and 2 measuring points at 70% of the upper arm length are marked on both sides. A gelpad is used to enable minimal compression. It is verified that the borders of the scan are blurred. Each measuring point is scanned in the short-axis and long-axis plane to more easily determine the subcutaneous adipose tissue and muscle structures especially in the presence of edema. First the quality of the scan is evaluated according to the visibility of the muscle fascia and bone surface. Then subcutaneous adipose tissue and entire muscle thickness are measured at the exact center of the scan drawing the shortest possible line from skin to bone surface. Discussion The illustrated description of the USVALID ultrasound method enables reproducibility by other researchers for external validity. The subject's position, the location of the measuring points, the performance and evaluation of the ultrasound scans are discussed and compared to other published ultrasound methodologies.