Effect of Nasal Continuous Positive Airway Pressure on The Pharyngeal Swallow in Neonates

Preterm infants with underdeveloped lungs and term infants with cardio-respiratory illness frequently need to be placed on ventilatory assistance. Nasal Continuous Positive Airway Pressure (NCPAP) has been proven to be an effective mode of noninvasive ventilation in neonates, as it delivers positive pressure to the airway throughout the respiratory cycle. NCPAP works by improving the breathing pattern in neonates; it increases the mean airway pressure, stents the upper airway, decreases proximal airway resistance, reduces physiological dead space, optimizes lung recruitment and improves diaphragmatic function. While many infants in the Neonatal Intensive Care Units (NICUs) require NCPAP, many of their other medical and developmental needs such as initiating oral feedings need to be addressed. Oral feeding of neonates while on NCPAP is a common practice in many NICUs, however the effect of such practice on neonatal swallowing mechanism has never been investigated.

Swallowing is a complex sensorimotor function that allows infant to safely and effectively ingest liquid nutrition. The ability of an infant to successfully feed is dependent on the precise interconnection of anatomy, physiology and neurology pathways. Afferent sequences play an integral role in the infant swallowing mechanism as sensory feedback is required during all phases of swallowing to allow appropriate positioning of anatomic structures, as well as to modulate the strength, velocity, and timing of muscle contractions. Sensory information is received from various types of sensory receptors distributed throughout the oral cavity, pharynx, larynx and esophagus. Localized areas of the infant's anatomy are known to have particular types of sensory receptors that are excited by specific stimuli which elicit appropriate motor movements.

One of the most densely populated sensory receptors are the mechanoreceptors which are sensitive to touch and pressure to help decipher the shape, texture, size and temperature of the bolus about to be swallowed. The mechanoreceptors are also sensitive to the pressure and movement of air flow during breathing.

The sensations perceived by these receptors are responsible for sending afferent sensory information to the medullary region of the brainstem where they are processed by the central pattern generators (CPGs). CPGs are composed of dedicated networks of interneurons that are responsible to sequence and activate different motor neurons at specified intensities to generate motor patterns. Both the swallowing CPG and the respiratory CPG are housed within the medulla. The close proximity of these neurons allows for precise swallow and breathing coordination. A close interrelationship between the swallowing and respiratory processes is further evident as they encompass shared anatomic structures and muscular components within the pharynx, and act as physiologically and biomechanically reciprocal events.

This close interrelationship between swallowing and breathing has led to some controversy and difference in opinion among neonatologists on the decision to start oral feedings while on NCPAP. Although there is no research directly related to the effect of NCPAP on swallowing process in neonates, NCPAP has been reported to induce dilatation of the laryngeal opening in preterm infants and inhibit the swallow reflex in adults.

For preterm infants, some neonatologists advocate initiation of oral feeds at 34 weeks gestational age, even if they require NCPAP; others strictly wait for NCPAP to be discontinued before oral feeding is established, fearing that infants may have difficulty coordinating breathing and swallowing acts, resulting in airway compromise. For term infants, many propose that oral feedings can be established once physiologic stability is demonstrated, either with or without NCPAP. Such controversies exist due to lack of evidence on the effect(s) of NCPAP on swallowing safety in human neonates.

To our knowledge no studies have been completed on human infants to evaluate the effect of NCPAP on the pharyngeal swallowing mechanism. Previous studies utilizing neonatal lambs, revealed that the application of NCPAP had no deleterious effect on cardiopulmonary safety, feeding efficiency and on nutritive swallowing- breathing coordination.

This study was designed with the aim to effectively assess the effects of NCPAP on the pharyngeal swallow mechanism in human neonates. The investigators hypothesize that the presence of NCPAP will lead to alterations in the sensorimotor sequence of the pharyngeal swallowing mechanism, increasing the risk for airway compromise and aspiration. The mechanoreceptors, which perceive sensory input from the liquid bolus, may be altered by the reception of continuous stream of airflow, provided by the NCPAP.