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BackgroundEffective lung protective ventilation requires reliable, real-time estimation of lung volume at the bedside. Neonatal clinicians lack a readily available imaging tool for this purpose.ObjectiveTo determine the ability of lung ultrasound (LUS) of the dependent region to detect real-time changes in lung volume, identify opening and closing pressures of the lung, and detect pulmonary hysteresis.MethodsLUS was performed on preterm lambs (n=20) during in vivo mapping of the pressure-volume relationship of the respiratory system using the super-syringe method. Electrical impedance tomography was used to derive regional lung volumes. Images were blindly graded using an expanded scoring system. The scores were compared with total and regional lung volumes, and differences in LUS scores between pressure increments were calculated.ResultsChanges in LUS scores correlated moderately with changes in total lung volume (r=0.56, 95% CI 0.47-0.64, p<0.0001) and fairly with right whole (r=0.41, CI 0.30-0.51, p<0.0001), ventral (r=0.39, CI 0.28-0.49, p<0.0001), central (r=0.41, CI 0.31-0.52, p<0.0001) and dorsal (r=0.38, CI 0.27-0.49, p<0.0001) regional lung volumes. The pressure-volume relationship of the lung exhibited hysteresis in all lambs. LUS was able to detect hysteresis in 17 (85%) lambs. The greatest changes in LUS scores occurred at the opening and closing pressures.ConclusionLUS was able to detect large changes in total and regional lung volume in real time and correctly identified opening and closing pressures but lacked the precision to detect small changes in lung volume. Further work is needed to improve precision prior to translation to clinical practice.

ObjectiveLung ultrasound (LUS) has shown promise as a diagnostic tool for the evaluation of the newborn with respiratory distress. No study has described LUS during ‘normal’ transition. Our goal was to characterise the appearance of serial LUS in healthy newborns from the first minutes after birth until airway liquid clearance is achieved.Study designProspective observational study.SettingSingle-centre tertiary perinatal centre in Australia.PatientsOf 115 infants born at ≥35 weeks gestational age, mean (SD) gestational age of 386/7weeks±11 days, mean birth weight of 3380±555 g, 51 were delivered vaginally, 14 via caesarean section (CS) after labour and 50 infants via elective CS.InterventionsWe obtained serial LUS videos via the right and left axillae at 1–10 min, 11–20 min and 1, 2, 4 and 24 hours after birth.Main outcome measuresLUS videos were graded for aeration and liquid clearance according to a previously validated system.ResultsWe analysed 1168 LUS video recordings. As assessed by LUS, lung aeration and airway liquid clearance occurred quickly. All infants had an established pleural line at the first examination (median=2 (1–4) min). Only 14% of infants had substantial liquid retention at 10 min after birth. 49%, 78% and 100% of infants had completed airway liquid clearance at 2, 4 and 24 hours, respectively.ConclusionsIn healthy transitioning newborn infants, lung aeration and partial liquid clearance are achieved on the first minutes after birth with complete liquid clearance typically achieved within the first 4 hours of birth.Trial registration numberANZCT 12615000380594.