Prolonged apnea associated with upper airway protective reflexes in apnea of prematurity

We examined the hypothesis that most idiopathic prolonged apneic spells in preterm infants originate as a form of upper airway protective reflex. We elicited a previously described upper airway reflex in 10 sleeping preterm infants with apnea of prematurity by instilling physiologic saline into the oropharynx and recording respiration, heart rate, and swallowing. Immediately after a small pharyngeal bolus of warm saline, one or more of several characteristic airway reflex responses occurred with most stimulus trials. These responses included brief central apnea, swallowing, and obstructed inspiratory efforts. Intermittently, this response pattern was more extensive and resulted in prolonged apnea. We compared the frequency of prolonged apnea immediately after saline boluses with spontaneously occurring prolonged apnea and found that apnea frequency after saline was greater than spontaneous apnea frequency in all 10 infants (p less than 0.0025). Also, the incidence of prolonged apnea occurring immediately after saline stimuli was significantly greater than that after randomly delivered control stimuli (p less than 0.005). These observations indicate that saline can induce prolonged apnea. Swallowing, a distinctive feature of the chemoreflex, occurred during 76% of spontaneous prolonged apnea spells. Spontaneous and postsaline prolonged apnea were nearly identical with respect to general features and frequency of specific airway protective responses. We conclude that the majority of spontaneous prolonged apneic spells in preterm infants have multiple features that are characteristic of an exaggerated airway protective response to an upper airway fluid stimulus. Circumstantial evidence suggests that endogenous upper airway secretions may be an important source of stimuli-inducing apneic spells in preterm infants.