Diaphragmatic ultrasonography: reference values and reliability for thickness, thickening fraction, and excursion in...

To establish reference values and assess the intra- and inter-rater reliability of inspiratory diaphragmatic thickness (IDT), expiratory diaphragmatic thickness (EDT), diaphragmatic thickening fraction (DTF), and diaphragmatic excursion (DE) using ultrasound, including the lower (LLN) and upper (ULN) limits of normality in neonates. This cross-sectional study included healthy neonates from a public hospital (July 2022-December 2023). IDT, EDT, DTF, and DE were measured by PT 1 (an experienced ultrasound physiotherapist). Reliability was assessed by having PT 1 and PT 2 (experts ultrasound physiotherapists) independently evaluate the exams twice using ImageJ software. Intraclass correlation coefficients (ICC) with 95% confidence intervals (CI) were calculated to assess intra- and inter-rater reliability. One hundred neonates were assessed [39 (38-40) weeks, 3168 ± 475 g, 49 (47.5-50) cm]. Reference values were EDT: 2.17 ± 0.59 mm, LLN: 2.05 mm and ULN: 2.29 mm; IDT: 1.71 ± 0.48 mm, LLN: 1.62 mm and ULN: 1.80 mm; DTF: 28.02 ± 9.88%, LLN: 26.08% and ULN: 29.96%; DE: 2.47 ± 0.72 mm, LLN: 2.33 mm and ULN: 2.61 mm. No significant differences were observed between the assessments of PT 1 and PT 2 (p > 0.05), intra- and inter-rater reliability were ICC ≥ 0.98 (0.97-1.00) (p < 0.001) and ICC ≥ 0.91 (0.85-0.99) (p < 0.001), respectively.

The established values support interpreting neonatal diaphragmatic function and detecting changes in contractility and motion range, with high intra- and inter-rater reliability for EDT, IDT, DTF, and DE.

• Diaphragmatic ultrasound is used to assess diaphragm function in various clinical contexts; however, its reliability and reference values for neonates are limited.

• Performing diaphragmatic ultrasound in neonates requires specific precautions to obtain accurate and reliable measurements. • The established normal, lower, and upper limits for diaphragmatic thickness and excursion support the functional assessment of the diaphragm in neonates by aiding in the detection of changes in contractility and movement, providing valuable reference values for clinical decision-making.