Lower limit of normality of the cross-sectional area of peripheral muscles and diaphragm measurements performed by ultrasound in newborns

The main respiratory muscle is the diaphragm. In newborns (NBs), due to their unfavorable biomechanics, this is prone to dysfunction. Premature babies (PTNB) have a deficit in fat-free mass. Given the difficulty of assessing muscle strength in NBs, kinesiological ultrasound (US) is an assessment that can be considered, however the gap that is observed on normal values for this population. <bold>AIMS:</bold> to stratify groups by gestational age and identify the lower limit of normality (LLN) for the cross-sectional area of peripheral muscles and excursion and thickening of the diaphragm in spontaneous breathing of full term (FTNB) and PTNB. <bold>METHODS:</bold> Cross-sectional study in which PTNB from 28 to 36 6/7 weeks of GA and FTNB from 37 to 42 weeks of GA were clinically stable, in room air. US was performed on the rectus femoris, tibialis anterior and biceps brachii muscles (cross-sectional area) and diaphragm (thickening and excursion). <bold>RESULTS:</bold> 120 NBs were evaluated and they were stratified into gestational age ranges (< 30 w- n=25; 31 to 35 w - n= 38; 36 w - n=23; > 37 w - n=34); there was a significant difference when comparing the cross-sectional area of the biceps and rectus femoris of newborns > 37 weeks compared to the other groups (p<0.05). There was a difference in diaphragm thickening (DTF%) in the group > 37 w and < 30 w. Regarding LLN, there was a significant difference between the groups >37 w and <30 w in all variables and this same group versus the other. <bold>CONCLUSION:</bold> It was possible to verify a difference in the size of peripheral muscle mass and DE between the groups and it was possible to establish normal values for FT na PTNB.