Apnea of Prematurity Apnea of prematurity (AOP) is the most common and Classification recurring problem of respiratory control in the premature AOP is distinguished by duration and hemodynamic dys- infant. AOP occurs in more than 85% of all infants born function and is further classified into three categories prior to 34 weeks gestational age. The incidence of AOP based on the presence or absence of obstruction. Cen- is inversely proportionate to gestational age at birth— tral apnea involves total cessation of respirations or the as gestational age decreases, apnea becomes more absence of respiratory muscle activity accompanied by prevalent. the absence of airflow. Obstructive apnea is character- ized by the presence of respiratory muscle activity in the In premature infants without respiratory distress syn- absence of airflow that continues throughout the entire drome (RDS), AOP may occur on the first day of life, but apnea episode. Mixed apnea consists of a combination it may not present for several days in infants with RDS. of obstructed apnea and central apnea and is believed to Many perinatal and postnatal complications increase the represent the most common type of apnea in the new- infant’s risk of developing AOP, including central nervous born. Obstructive apnea may occur in the pharynx, the system insult or injury, respiratory insult or injury, meta- larynx, or in both areas of the upper airway. Ideopathic bolic disease, sepsis, congenital defects, inborn errors of apnea is most commonly associated with prematurity. metabolism, birth trauma, and maternal substance use (including smoking and alcohol consumption). Some evi- Hypoxemic events resembling apnea have been detected dence supports heredity as a risk factor. in intubated, mechanically ventilated preterm infants. These episodes of hypoxemia are preceded by increased Definition pulmonary resistance and decreased compliance similar AOP is most commonly defined as the cessation of to events occurring before apnea in unintubated infants. breathing for more than 20 seconds, or 5–10 seconds in Subtle, spontaneous movements precede these episodes, the presence of bradycardia (heart rate < 80 bpm or 30 and they are characterized by central respiratory depres- bpm below baseline) or desaturations (SaO < 80%–85%). 2 sion and obstructed airflow. The events are a conse- Brief respiratory pauses that are less than 10 seconds in quence of hypoventilation and are frequently associated duration and not associated with bradycardia or desatu- with arousal. rations can occur in conjunction with startles, movement, defecation, or asynchrony during feedings, and are usu- Periodic Breathing ally self-limiting. AOP should be distinguished from periodic breathing, in which the infant exhibits regular short cycles (10–20 sec- In the premature infant, apnea may be the presenting onds in length) of respiration that are interrupted by respi- symptom accompanying altered homeostasis of nearly ratory pauses of at least 3 seconds. The pattern recurs for all organ systems. Temperature instability, asphyxia or at least 2 minutes followed by a stronger respiratory drive hypoxemic events, sepsis, metabolic disturbances, respi- to restore normal ventilation and often is accompanied by ratory compromise, patent ductus arteriosus or other mild hypoxemia. Periodic breathing is considered a benign heart defects, intracranial hemorrhage, feeding disrup- developmental phenomenon, and medical treatment is tions, hematologic disturbances, pain, and agitation are not indicated. However, when preceded by significant some examples. AOP is considered a diagnosis of exclu- hypoxemia or when associated with bradycardia or pro- sion because it often is the presenting symptom of other longed apnea with alveoloar hypoventilation, it is abnor- pathologic conditions and should be thoroughly investi- mal and may be a precursor to pathologic apnea. gated before being assigned this diagnosis. 207 Baby Steps to Home © 2018 by the National Association of Neonatal Nurses Diagnoses AOP and periodic breathing are disorders that tend to Significant ventilatory and cardiovascular consequences decline in frequency with advancing postconceptual age can be associated with AOP. Prolonged apnea results in and are treated with administration of methylxanthines. hypoxemia and hypercarbia, which is directly related to the frequency, duration, and intensity of the episode. Pathophysiology AOP is a common disorder of respiratory control in pre- Apnea and Gastroesophageal Reflux mature infants. Apnea presenting independent of other Gastroesophageal reflux (GER) is a common problem in pathology is most likely a maturational feature repre- premature infants and often is suggested as a compo- senting a physiologic rather than pathologic immatu- nent of AOP. Reflux of gastric contents into the larynx may rity of respiratory control. However, a clear mechanism induce apnea as a result of stimulation of the laryngeal responsible for apnea in premature infants has not been nerve or other afferent pathways; however, this mech- identified. anism is not proven to either cause or prolong apnea. The frequency with which the two conditions coexist is Normal rhythmic breathing requirements include a pat- debated, and the cause-effect relationship is multifacto- ent airway; a central respiratory drive originating from rial. The majority of apnea occurring before GER is cen- respiratory centers in the brainstem (modulated by input tral in origin, but when apnea occurs during or after a from peripheral neural and chemical receptors); and coor- GER episode, it is more frequently mixed apnea. In some dinated, effective functioning muscles of respiration. instances, apnea occurs prior to reflux, decreasing lower Changes in arterial PCO2, PO2, and pH act on neural and esophageal tone and lower esophageal sphincter pres- chemical receptors from these centers and are integrated sure resulting in reflux. In the overall premature infant by the respiratory center in the brainstem, which sends population, GER does not induce apnea, prolong the dura- signals to the respiratory muscles responsible for main- tion of apnea, or exacerbate apnea-related bradycardia taining airway patency and regulating the level of ven- or desaturations. Further, there is no clear evidence that tilation. The immature brainstem respiratory centers in pharmacologic agents that decrease gastric acidity or preterm infants have an attenuated response to carbon enhance gastrointestinal motility impact the frequency or dioxide and a paradoxical response to hypoxia, which duration of apnea. results in apnea rather than the normal hyperventilation Management response. Anatomical characteristics such as decreased Management begins by eliminating factors associated number of synaptic connections, decreased dendritic with increasing risk of apnea, by taking measures such arborization, and poor myelination result in functional as ensuring a stable thermal environment, maintain- immaturity of the brainstem, which improves after treat- ing airway patency, and using proper positioning. Ensur- ment with methyxanthines. ing proper placement of nasal and oral gastric tubes is important, as malposition of these tubes has been impli- Obstructive apnea can be the result of poor pharyngeal cated in association with apnea. Cue-feeding, pacing with tone, which can cause the pharynx to collapse with neg- feedings, and left-side lying position are good measures ative airway pressures generated during inspiration. for parents to facilitate better feeding patterns, which Structurally, the airways are more compliant and smaller, may reduce the incidence of choking and apnea. Prone both in diameter and length, and are at increased risk for positioning of the preterm infant assists to “splint” the blockage by malpositioning, edema, and excess mucus. chest wall and facilitate slight neck extension positioning and stabilization of the head; this positioning has been Genetic factors associated with a higher risk of occurrence shown to improve breathing. Prone positioning in the in premature infants include being born to first-degree con- preterm infant also is associated with improved gastric sanguineous parents, being monozygotic twins, and having emptying time. Prone positioning is indicated only with a sibling who presents with complications of apnea. 208 Baby Steps to Home © 2018 by the National Association of Neonatal Nurses Diagnoses the use of cardiorespiratory monitoring, and the impor- Doxapram, another respiratory stimulant, has been used tance of transitioning to supine positioning for home care in infants with idiopathic apnea of prematurity refrac- cannot be over emphasized. tory to methylxanthines. It acts through stimulation of a peripheral chemoreceptor and has been shown to Administering continuous airway pressure is associ- increase minute ventilation, tidal volume, inspiratory ated with decreased apnea. Evidence suggests it may flow, and airway pressure. Side effects include hyperten- serve as a “splint” for upper airways and the chest wall, sion, irritability, hypoglycemia, gastric irritability, and in a increase oxygenation, and help maintain functional resid- small number of preterm infants, heart block. Doxapram ual capacity. Many times, the flow is enough to support is available as an oral drug, but it is poorly absorbed. the infant with apnea, but sometimes administration of Because of this, it is typically used as a continuous IV oxygen along with flow is necessary. Continuous posi- infusion.