The Increase in Diaphragm Thickness in Preterm Infants is Related to Birth Weight: A Pilot Study

Abstract

Purpose Diaphragm ultrasound (DU) has been used in adult and pediatric critical patients in relation to prediction of extubation success or to detect diaphragm dysfunction, but there is a lack of evidence in neonates. Our aim is to study the evolution of diaphragm thickness in preterm infants, as well as related variables. Methods Prospective monocentric observational study that included preterm infants born before 32 weeks (PT32). We performed DU to measure right and left inspiratory and expiratory thickness (RIT, LIT, RET and LET) and calculated the diaphragm-thickening fraction (DTF) in the first 24 hours of life and then weekly until 36 weeks postmenstrual age, death, or discharge. Using multilevel mixed-effect regression, we evaluated the influence of time since birth on diaphragm measurements, as well as bronchopulmonary dysplasia (BPD), birth weight (BW) and days of invasive mechanical ventilation (IMV). Results We included 107 infants, and we performed 519 DUs. All diaphragm thickness increased with time since birth, but the only additional variable that influenced this growth was BW: beta coefficients RIT=0.00006; RET=0.00005; LIT=0.00005; LET=0.00004, p<0.001. Right DTF values remained stable since birth. Conclusions In our population we found that the higher the BW, the higher diaphragm thicknesses at birth and follow-up. Contrary to the previously published findings in adult and pediatric settings, we were unable to describe a relationship between days of IMV and diaphragm thickness in PT32. The final diagnosis of BPD does not influence this increase either.