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Hypoxia inhibits breathing and causes the glottis to close in preterm rabbit kittens at birth
Indya M Davies1,2, Emily Crameri1,2, Megan J Wallace1,2
1The Ritchie Centre, Hudson Institute of Medical Research, Melbourne, VIC, Australia.
Background:
Apnea in newborns causes the glottis to adduct and prevents gas from entering the lungs. As hypoxia is an inhibitor of fetal breathing, we have investigated the effect of hypoxia on glottis patency and breathing in preterm newborn rabbits.
Methods:
Rabbit kittens (29 d gestation, term ~32 d; n = 12) were delivered by c-section, fitted with a custom face mask and oesophageal catheter to measure breathing efforts. After birth, kittens underwent phase contrast X-ray imaging while receiving CPAP using the following sequence of gases: (i) room-air, (ii) 100% oxygen, (iii) 100% nitrogen and (iv) 100% oxygen again. Glottis patency was visually assessed to determine %time that the glottis was open in each gas.
Results:
The glottis remained open for longer (44.7 ± 1.8% vs. 15.5 ± 1.8%, p < 0.0001) and breathing rates were higher (18.1 ± 0.5 breaths/min vs. 11.3 ± 1.1 breaths/min, p = 0.0001) when kittens were exposed to 100% oxygen compared to room-air. When exposed to 100% nitrogen, breathing became unstable and resulted in apnea and a fully closed glottis in all kittens. Glottis patency and breathing were restored by resuscitating with 100% oxygen.
Conclusion:
These results highlight the importance of avoiding hypoxia and promoting stable breathing to ensure the glottis is open when giving CPAP.
Impact:
While preterm newborns commonly receive non-invasive respiratory support (CPAP) in the delivery room, this can be ineffective, particularly if the infant is apneic. We have demonstrated that hypoxia induces unstable breathing patterns in preterm newborn kittens, eventually causing apnea. When breathing is unstable, the glottis opens but only during inspiration. Between breaths and during apnea, the glottis remains closed, which prevents effective delivery of CPAP via face mask. This study highlights that adequate oxygenation is critically important for maintaining breathing activity and the use of oxygen in the delivery room can enhance the effectiveness of non-invasive respiratory support.
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