335 - Elevated Airway Liquid Volume At Birth Alters Respiratory Control In Spontaneously Breathing Near-Term Lambs

Sunday, April 30, 2023

3:30 PM – 6:00 PM ET

Poster Number: 335
Publication Number: 335.345

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; Emily J. Pryor, Monash University, Melbourne, Victoria, Australia; Karyn Rodgers, Hudson Institute, Mekbourne, 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: Respiratory distress in infants born at or near term ( >37 weeks gestation) most commonly occurs in infants born by caesarean section (CS) without labour (i.e., elective CS). Elevated airway liquid volumes at birth, which is common following elective CS (~35-45mL/kg at term), markedly reduces lung function after birth, but its effect on newborn respiratory control is unknown.

Objective: We aimed to investigate the effect of elevated airway liquid volume at birth on respiratory control and cardiorespiratory function in spontaneously breathing newborn lambs.

Design/Methods:

Near-term fetal lambs were partially exteriorised, instrumented (137 days gestation; term ~147 days) and returned to the uterus 3 days before delivery. Prior to delivery at 140 days gestation, airway liquid volumes were drained to simulate the effect of labour (Controls n=7) or drained and replaced with 20 mL/kg liquid to reflect the volume expected after CS with no labour (elevated liquid; EL n=10). Lambs were then delivered via CS under maternal sedation and spinal anaesthesia. Spontaneously breathing lambs were supported with supplemental oxygen using nasal high flow if required (to maintain oxygenation >90%). Lambs received enteral formula feeds as required. Breathing patterns and cardiorespiratory physiological measures were analysed during the first four hours after birth.

Results:

During the first four hours after birth, EL lambs had poorer gas exchange indicated by lower SaO₂/FiO₂ ratio (p=0.0009) and lower arterial pH (p=0.035) compared to controls. EL lambs spent a greater proportion of time displaying abnormal respiratory patterns including tachypnea, grunting and expiratory braking maneuvers after birth (28±5% vs. 46±5%, p=0.025). Significantly more grunting occurred within the first hour after delivery in the EL lambs, compared to subsequent hours (29±9% vs. 2±1%, 1^st hour vs. 4^th hour, p=0.0003). EL lambs were also less active (p=0.033) and consumed less milk than controls after delivery (230±39 vs. 98±22 mL, p=0.008).

Conclusion(s):

We have identified and categorised both normal and abnormal breathing patterns in spontaneously breathing near-term newborn lambs during the first four hours after birth. Elevated airway liquid volumes at birth contributed to poor gas exchange, altered respiratory control mechanisms, and increased the risk of developing tachypnea and expiratory braking. This pre-clinical model provides important insights into the respiratory control mechanisms underlying respiratory distress commonly observed in term infants following elective CS.