ImportanceICU-acquired muscle atrophy occurs commonly and worsens outcomes in adults. The incidence and severity of muscle atrophy in critically ill children are poorly characterized.ObjectiveTo determine incidence, severity and risk factors for muscle atrophy in critically ill children.Design, setting and participantsA single-center, prospective cohort study of 34 children receiving invasive mechanical ventilation for ≥48 hours. Patients 1 week– 18 years old with respiratory failure and without preexisting neuromuscular disease or skeletal trauma were recruited from a tertiary Pediatric Intensive Care Unit (PICU) between June 2015 and May 2016. We used serial bedside ultrasound to assess thickness of the diaphragm, biceps brachii/brachialis, quadriceps femoris and tibialis anterior. Serial electrical impedance myography (EIM) was assessed in children >1 year old. Medical records were abstracted from an electronic database.ExposuresRespiratory failure requiring endotracheal intubation for ≥48 hours.Main outcome and measuresThe primary outcome was percent change in muscle thickness. Secondary outcomes were changes in EIM-derived fat percentage and “quality”.ResultsOf 34 enrolled patients, 30 completed ≥2 ultrasound assessments with a median interval of 6 (IQR 6–7) days. Mean age was 5.42 years, with 12 infants <1 year (40%) and 18 children >1 year old (60%). In the entire cohort, diaphragm thickness decreased 11.1% (95%CI, -19.7% to -2.52%) between the first two assessments or 2.2%/day. Quadriceps thickness decreased 8.62% (95%CI, -15.7% to -1.54%) or 1.5%/day. Biceps (-1.71%; 95%CI, -8.15% to 4.73%) and tibialis (0.52%; 95%CI, -5.81% to 3.40%) thicknesses did not change. Among the entire cohort, 47% (14/30) experienced diaphragm atrophy (defined a priori as ≥10% decrease in thickness). Eighty three percent of patients (25/30) experienced atrophy in ≥1 muscle group, and 47% (14/30)—in ≥2 muscle groups. On multivariate linear regression, increasing age and traumatic brain injury (TBI) were associated with greater muscle loss. EIM revealed increased fat percentage and decreased muscle “quality”.Conclusions and relevanceIn children receiving invasive mechanical ventilation, diaphragm and other skeletal muscle atrophy is common and rapid. Increasing age and TBI may increase severity of limb muscle atrophy. Prospective studies are required to link muscle atrophy to functional outcomes in critically ill children.

Introduction The radial and posterior interosseous nerves (PIN) are prone to injury at multiple sites. Electrodiagnostic (EDX) studies may only identify the most proximal lesion. Nerve ultrasound could augment electrodiagnosis by visualizing additional pathology. Methods Retrospective examination of ultrasound and electrodiagnosis from 26 patients evaluated for posterior cord/radial/PIN lesions. Results Eighteen of 26 patients had abnormalities on electrodiagnosis (15 radial; 2 PIN; 1 posterior cord). Ultrasound identified 15 of 18 (83%) of the EDX abnormalities and provided additional diagnostic information. In 6 of 15 (40%) patients with EDX evidence of radial neuropathy, ultrasound identified both radial nerve enlargement and additional, unsuspected PIN enlargement (53% to 339% enlarged vs. unaffected side). Ultrasound also identified: nerve (dis)continuity at the trauma site (n=8); and nerve tumor (n=2; 1 with normal EDX). Conclusion In radial neuropathy, ultrasound often augments EDX studies and identifies a second lesion in the PIN. Further studies are required to determine the etiology and significance of this additional distal pathology.

A trainee with at least 2 months of experience can reliably measure upper limb nerves. Reliability varies by nerve and location and slightly improves with time. Muscle Nerve 57: 189-192, 2018.

Muscle thickness is reliably measured using ultrasound by trained examiners in critically-ill children. Our approach detects atrophy >13% in limb and >38% in diaphragm muscles. The smaller detectable change in limb muscles is likely due to their greater thickness. This article is protected by copyright. All rights reserved.