Assessing lung aeration using ultrasound after birth in near-term lambs at risk of respiratory distress

E J Pryor; I M Davies; K J Crossley; A M Thiel; E V McGillick; K Rodgers; I Nitsos; M J Kitchen; D A Blank; S B Hooper

doi:10.3389/fped.2023.1148443

Assessing lung aeration using ultrasound after birth in near-term lambs at risk of respiratory distress

Front Pediatr. 2023 May 22:11:1148443. doi: 10.3389/fped.2023.1148443. eCollection 2023.

Authors

E J Pryor^{1

2}, I M Davies^{1

2}, K J Crossley^{1

2}, A M Thiel^{1

2}, E V McGillick^{1

2}, K Rodgers^{1

2}, I Nitsos^{1

2}, M J Kitchen³, D A Blank^{1

4}, S B Hooper^{1

2}

Affiliations

¹ The Ritchie Centre, Hudson Institute of Medical Research, Melbourne, VIC, Australia.
² Department of Obstetrics and Gynaecology, Monash University, Melbourne, VIC, Australia.
³ School of Physics and Astronomy, Monash University, Melbourne, VIC, Australia.
⁴ Monash Newborn, Monash Children's Hospital, Clayton, VIC, Australia.

Abstract

Background: Optimizing respiratory support after birth requires real-time feedback on lung aeration. We hypothesized that lung ultrasound (LUS) can accurately monitor the extent and progression of lung aeration after birth and is closely associated with oxygenation.

Methods: Near-term (140 days gestation, term ∼147 days), spontaneously breathing lambs with normal (controls; n = 10) or elevated lung liquid levels (EL; n= 9) were delivered by Caesarean section and monitored for four hours after birth. LUS (Phillips CX50, L3-12 transducer) images and arterial blood gases were taken every 5-20 min. LUS images were analyzed both qualitatively (grading) and quantitatively (using the coefficient of variation of pixel intensity (CoV) to estimate the degree of lung aeration), which was correlated with the oxygen exchange capacity of the lungs (Alveolar-arterial difference in oxygen; AaDO₂).

Results: Lung aeration, measured using LUS, and the AaDO₂ improved over the first 4 h after birth. The increase in lung aeration measured using CoV of pixel intensity, but not LUS grade, was significantly reduced in EL lambs compared to controls (p = 0.02). The gradual decrease in AaDO₂ after birth was significantly correlated with increased lung aeration in both control (grade, r²= 0.60, p < 0.0001; CoV, r²= 0.54, p < 0.0001) and EL lambs (grade, r²= 0.51, p < 0.0001; CoV, r²= 0.44, p < 0.0001).

Conclusions: LUS can monitor lung aeration and liquid clearance after birth in spontaneously breathing near-term lambs. Image analysis techniques (CoV) may be able detect small to moderate differences in lung aeration in conditions with lung liquid retention which are not readily identified using qualitative LUS grading.

Keywords: lung ultrasound; lung ultrasound (LUS); neonate; respiratory distress - transient tachypnoea of newborn or 'wet lung syndrome'; respiratory distress at birth; support.

Grants and funding

This research was supported by a National Health and Medical Research Council (NHMRC) Ideas Grant (2012443) and Program Grant (APP113902) as well as the Victorian Government’s Operational Infrastructure Support Program. EJ Pryor and I Davies were supported by Australian Government Research Training Program Scholarships. EV McGillick was supported by a NHMRC Peter Doherty Biomedical Early Career Fellowship (APP1138049). SB Hooper was supported by a NHMRC Principal Research Fellowship (APP1058537).