328 - Respiratory Patterns In Spontaneously Breathing Near-term Newborn Lambs At High And Low Risk Of Respiratory Distress

Sunday, April 30, 2023

3:30 PM – 6:00 PM ET

Poster Number: 328
Publication Number: 328.345

Indya M. Davies, Hudson Institute of Medical Research, Clayton, Victoria, Australia; Erin V. McGillick, Hudson Institute of Medical Research/Monash University, Clayton, Victoria, Australia; Kelly J. Crossley, Hudson Institute of Medical Research, Clayton, Victoria, Australia; Ilias Nitsos, Hudson Institute of Medical Research, Clayton, Victoria, Australia; alison Thiel, Hudson Institute, Clayton, Victoria, Australia; Arjan te pas, Leiden University Medical Center, Leiden, Zuid-Holland, Netherlands; Stuart Hooper, Monash University, Melbourne, Victoria, Australia; Valerie Anne. Zahra, Hudson Institute, Clayton, Victoria, Australia

Presenting Author(s)

kelly J. Crossley, PhD (she/her/hers)

Senior Research Fellow
Hudson Institute of Medical Research
Clayton, Victoria, Australia

Co-Author(s)

Indya M. Davies, BScHons (she/her/hers)

PhD Student
Hudson Institute of Medical Research
Clayton, Victoria, Australia

Background: Ovine models have been used to investigate the physiological transition from fetal to newborn life, but have typically used lambs delivered via caesarean section (CS) under general anaesthesia that were subsequently intubated and mechanically ventilated. This is not ideal as (i) general anaesthesia causes neonatal respiratory depression and (ii) intubation and mechanical ventilation prevents observations of intrinsic respiratory control. As a result, little is known of the respiratory patterns in spontaneously breathing newborns during transition, particularly in newborns at risk of developing respiratory distress (RD).

Objective: We aimed to develop an experimental model to deliver spontaneously breathing near-term lambs and to categorise breathing patterns after birth.

Design/Methods: Near-term fetal lambs (n=25) were partially exteriorised, instrumented and returned to the uterus, 2-3 days prior to delivery (137 days gestation; term ~147 days). At 140 days gestation, lambs were delivered via caesarean section under light maternal sedation (midazolam) and spinal anaesthesia. Lambs were stimulated to spontaneously breathe while attached to the cord and supported with high flow oxygen therapy if required (oxygen saturation maintained >90%). The umbilical cord was clamped only after stable breathing was established. Breathing patterns were assessed by measuring intrapleural and upper-tracheal pressures during the first four hours after birth.

Results:

Five distinct breathing patterns were identified including: i) quiet (tidal) breathing, ii) breathing during active periods, iii) breathing during feeding, iv) tachypnea and v) expiratory braking maneuvers. Lambs at low risk of RD spent the largest proportions of time displaying quiet breathing (34±6%), active periods (30±3%) and feeding (8±1%) over four hours. Expiratory braking (grunting) was most observed within the first 60 minutes after delivery and resolved over time. Quiet breathing was more common after 60 minutes when the lambs had stabilised after delivery. In lambs at high risk of RD, features including hypoxemia, nasal flaring and intercostal retractions were also observed.

Conclusion(s):

Using our model of spontaneously breathing near-term lambs we have identified and categorised both normal and abnormal breathing patterns during the first four hours after birth. This pre-clinical model can be used to study respiratory behaviours after birth and the efficacy of respiratory support in newborns with RD.