Point-of-Care Ultrasound to Measure Muscle Cross-Sectional Area in Preterm and Term Infants: A Feasibility Study

Abstract Background/Objective: Lean body mass is linked to improved outcomes, but infant muscle assessment tools are limited. Point-of-care ultrasound (POCUS) measurements of muscle cross-sectional area (CSA) may overcome these limitations. Study Design: A prospective cohort of 60 infants at two level IV NICUs underwent serial POCUS biceps CSA, rectus femoris CSA, and anthropometric measurements. Intraclass correlation coefficients (ICC) assessed reliability of CSA measurements. Linear mixed models examined associations between muscle CSA and growth, postmenstrual age (PMA), and nutrition. Results Intra- and inter-rater ICCs ranged from 0.92 to 0.99 and from 0.77 to 0.91, respectively. No safety events occurred. Biceps CSA correlated with PMA, weight, length, head circumference, and mid-upper arm circumference (p < 0.01). Rectus femoris CSA correlated with PMA, weight, head circumference, mid-thigh circumference, and protein intake (p < 0.01). Conclusion POCUS is feasible, safe, and reliable for muscle CSA measurement in NICU infants. Validation against gold-standard tools is needed.