Muscle Ultrasound Changes and Physical Function of Critically Ill Children: A Comparison of Rectus Femoris Cross-Sectional Area and Quadriceps Thickness Measurements.

Unlabelled: Quadriceps thickness (QT) and rectus femoris cross-sectional area (RF) are both used to evaluate muscle changes in critically ill children. However, their correlation and association with physical function has not been compared.

Objectives: To compare QT with RF changes, and their association with physical function in critically ill children.

Design Setting And Participants: Secondary analysis of a prospective cohort study of children 0-18 years old admitted to a tertiary mixed PICU between January 2015 and October 2018 with PICU stay greater than 48 hours and greater than or equal to one organ dysfunction.

Main Outcomes And Measures: Ultrasound QT and RF were measured at PICU admission, PICU discharge, hospital discharge, and 6 months post-discharge. QT and RF changes from baseline were compared with each other and with change in motor function, physical ability, and physical health-related quality of life (HRQOL).

Results: Two hundred thirty-seven images from 66 subjects were analyzed. RF change was not significantly different from QT change at PICU (-8.07% [interquartile range (IQR), -17.11% to 4.80%] vs -4.55% [IQR, -14.32% to 4.35%]; = 0.927) or hospital discharge (-5.62% [IQR, -15.00% to 9.42%] vs -8.81% [IQR, -18.67% to 2.39%]; = 0.238) but was significantly greater than QT change at 6 months (32.7% [IQR, 5.74-109.76%] vs 9.66% [IQR, -8.17% to 25.70%]; < 0.001). Motor function change at PICU discharge was significantly associated with RF change (adjusted β coefficient, 0.02 [95% CI, 0.01-0.03]; = 0.013) but not QT change (adjusted β coefficient, -0.01 [95% CI, -0.02 to 0.01]; = 0.415). Similar results were observed for physical HRQOL changes at hospital discharge (adjusted β coefficient for RF change, 0.51 [95% CI, 0.10-0.92]; = 0.017 and adjusted β coefficient for QT change, -0.21 [-0.76 to 0.35]; = 0.458). Physical ability was not significantly associated with RFCSA or QT changes at 6 months post-discharge.

Conclusions And Relevance: Ultrasound derived RF is associated with PICU motor function and hospital discharge physical HRQOL changes, unlike QT, and may be more useful for in-hospital muscle monitoring in critically ill children.