626 - Body Composition and Muscle Mass Assessment Using Point-Of-Care Ultrasound in the Neonatal Intensive Care Unit

Publication Number: 626.3606

Stephanie Yeager, Seattle Children's/University of Washington, Seattle, WA, United States; D. Taylor Hendrixson, University of Washington School of Medicine, Seattle, WA, United States; Guilherme M. Cunha, University of Washington School of Medicine, Seattle, WA, United States; Gregory C.. Valentine, University of Washington School of Medicine, Tacoma, WA, United States; Katie M. Strobel, University of Washington School of Medicine, Seattle, WA, United States

Background: Fat-free mass accretion is associated with improved neurodevelopment and metabolic health in preterm infants. Current body composition methods are not feasible in ill infants admitted to the neonatal intensive care unit (NICU). Determining the utility of point-of-care ultrasound (POCUS) for body composition assessment in NICU infants is important to help guide precision nutrition for vulnerable premature infants.

Objective: This study’s objective is to (1) assess if ultrasound measurements of rectus femoris and biceps muscle cross-sectional area (CSA) in NICU infants are feasible, safe, and reliable and (2) investigate the relationship between biceps and rectus femoris muscle CSA with infant growth anthropometrics.

Design/Methods: We conducted a pilot, prospective observational study recruiting infants from 24 to 46 weeks admitted to the NICU. Data collection included rectus femoris and biceps muscle ultrasounds, mid-upper arm, mid-thigh and abdominal circumference, foot length, and standard anthropometrics.
Three images of each muscle were obtained per ultrasound session. For twenty subjects, a second neonatologist also obtained a single image of each muscle. A radiologist reviewed images to ensure accuracy. Muscle CSA was calculated using offline image software. Intra-rater and inter-rater reliability were measured using intraclass correlations. Linear mixed regression models adjusting for sex and gestational age were conducted to assess for associations between muscle CSA and infant growth parameters.

Results: Sixty subjects were enrolled in this study from July 2023 to August 2024. Median (IQR) gestational age was 33.1 (31.4-36.2) and birth weight z-score was -0.10 (-0.62-0.43). There were no study-related adverse safety events. Ultrasound CSA measurements had acceptable intra-rater and inter-rater reliability (Table 1). Ultrasound derived biceps and rectus femoris muscle CSA are positively associated with corrected gestational age (Figure 1, p < 0.0001)). Biceps muscle CSA is positively associated with infant weight, length and head circumference z-scores (Table 2). Rectus muscle CSA is positively associated with infant weight and head circumference z-scores (Table 2).

Conclusion(s): Infant biceps and rectus femoris muscle ultrasounds are feasible, safe and reliable. Biceps and rectus femoris CSA strongly associate with gestational age and infant anthropometrics. With further validation, ultrasound could become a clinically applicable tool to trend fat-free mass accrual and help promote growth in the NICU.

Table 1.
Ultrasound measurements of muscle cross-sectional area demonstrate A) intra-rater reliability and B) inter-rater reliability (ICC: intra-class correlation, CI: confidence interval).

Figure 1.
Ultrasound derived A) biceps and B) rectus femoris muscle cross-sectional area (CSA) is positively associated with corrected gestational age (CGA) (p <0.0001). Color scale represents individual subject.

Table 2.
Linear mixed models of biceps and rectus femoris cross sectional area (CSA) and their relationship to anthropometric z-scores. All models adjusted for repeated measures, corrected gestational age, and sex.

Table 1.
Ultrasound measurements of muscle cross-sectional area demonstrate A) intra-rater reliability and B) inter-rater reliability (ICC: intra-class correlation, CI: confidence interval).

Figure 1.
Ultrasound derived A) biceps and B) rectus femoris muscle cross-sectional area (CSA) is positively associated with corrected gestational age (CGA) (p <0.0001). Color scale represents individual subject.

Table 2.
Linear mixed models of biceps and rectus femoris cross sectional area (CSA) and their relationship to anthropometric z-scores. All models adjusted for repeated measures, corrected gestational age, and sex.