Laryngeal closure impedes non-invasive ventilation at birth

Abstract

Background: Non-invasive ventilation is sometimes unable to provide the respiratory needs of very premature infants in the delivery room. While airway obstruction is thought to be the main problem, the site of obstruction is unknown. We investigated whether closure of the larynx and epiglottis is a major site of airway obstruction.

Methods: We used phase contrast X-ray imaging to visualise laryngeal function in spontaneously breathing premature rabbits immediately after birth and at approximately 1 hour after birth. Non-invasive respiratory support was applied via a facemask and images were analysed to determine the percentage of the time the glottis and the epiglottis were open.

Hypothesis: Immediately after birth, the larynx is predominantly closed, only opening briefly during a breath, making non-invasive intermittent positive pressure ventilation (iPPV) ineffective, whereas after lung aeration, the larynx is predominantly open allowing non-invasive iPPV to ventilate the lung.

Results: The larynx and epiglottis were predominantly closed (open 25.5%±1.1% and 17.1%±1.6% of the time, respectively) in pups with unaerated lungs and unstable breathing patterns immediately after birth. In contrast, the larynx and the epiglottis were mostly open (90.5%±1.9% and 72.3%±2.3% of the time, respectively) in pups with aerated lungs and stable breathing patterns irrespective of time after birth.

Conclusion: Laryngeal closure impedes non-invasive iPPV at birth and may reduce the effectiveness of non-invasive respiratory support in premature infants immediately after birth.

Keywords: Non-invasive ventilation; apnoea; glottis; larynx; preterm newborn.

Figure 1

Phase-contrast X-ray images of a spontaneously breathing newborn preterm rabbit pup with (A) a closed glottis and epiglottis and (B) an open glottis and epiglottis; the inserts are magnifications of the regions shown within the white boxes. (C) Air accumulation in the stomach of a rabbit pup that did not have an oesophageal tube and received CPAP levels >7 cmH₂O while the larynx was closed. CPAP, continuous positive airway pressure.

Figure 2

Flow diagram describing the outcome of the preterm rabbit pups with respect to developing a stable or unstable breathing pattern immediately after birth and at approximately 1 hour after birth.

Figure 3

Intrathoracic oesophageal pressure recordings from preterm rabbit pups displaying (A) an unstable breathing pattern or (B) a stable continuous breathing pattern. Each reduction in pressure represents a breath. Both recordings were obtained within a few minutes of birth. The unstable breathing pattern was characterised by breaths that differed in amplitude, varied in rate and were interspersed with apnoeic periods; these profiles were accompanied with a bradycardia of <100 beats per minute. In contrast, the stable breathing pattern was characterised by regular, continuous breathing that was relatively consistent in amplitude.

Figure 4

Physiological recordings of airway pressures (P _aw) and oesophageal pressures (P _oesoph) in preterm rabbit pups that initially had a stable spontaneous breathing pattern. (A) The pup received iPPV using a peak inspiratory pressure of 25 cmH₂O and an end-expiratory pressure of 5 cmH₂O. Note that the iPPV resulted in positive pressure fluctuations in oesophageal pressure, demonstrating transmission of ventilation pressure into the chest that resulted in lung inflations; lung inflation was confirmed from X-ray imaging. (B) The pup received CPAP that when increased to 8 cmH₂O, caused an immediate suppression of spontaneous breathing activity that persisted throughout the elevated CPAP period; only one large deep inspiratory effort was observed. Note that although P _aw increased with increased CPAP, oesophageal pressure did not increase, indicating that the pressure was not transmitted into the chest because the larynx was closed. CPAP, continuous positive airway pressure; iPPV, intermittent positive pressure ventilation.

Figure 5

The percentage of time that the glottis (top panel) and epiglottis (bottom panel) were open in preterm rabbit pups measured within minutes of birth (A and C) and at approximately 1 hour after birth (B and D). (A and C) Pups were divided into two groups depending on whether they had a stable (closed circles) or unstable breathing pattern after birth (closed squares; see figure 3).

Figure 6

Simultaneous changes in airway pressure (black) and percentage change in pharyngeal diameter (blue) measured during intermittent positive pressure ventilation in a preterm rabbit pup. Measurements of pharyngeal diameter were obtained from consecutive phase-contrast X-ray images and were measured at both peak inflation and near end-expiration at precisely the same point in the pharynx.