It is important to characterize the event with a comprehensive history, paying particular attention to changes in breathing, skin color, muscle tone, and level of consciousness. To differentiate normal from potentially pathologic events, determine what occurred before, during and after the event as well as the relationship of the event to feeding, sleeping, and upper and lower respiratory problems.
Changes in breathing: Many newborns experience physiologic patterns of breathing that can be frightening to a layperson but are normal. Healthy infants often have cyclic periods of rapid breathing interposed with respiratory pauses, termed periodic breathing. Periodic breathing is observed in nearly all pre-term and most term infants, and lasts until about 2 months of age in term infants. In addition, irregular respirations are the hallmark of active sleep (later referred to REM sleep or dream sleep) at all ages. Irregular breathing during REM continues into adulthood and is normal.
Apnea is typically characterized as central, obstructive, or mixed. Apneic pauses of >20 seconds or those associated with changes in color, tone, or heart rate are considered pathologic. Apnea is difficult to characterize subjectively, so the new AAP BRUE guideline includes any brief and resolved irregularity in respiration as a component of BRUE, unlike the ALTE definition which specified apnea. Central apnea implies a disruption in the central respiratory centers resulting in a cessation of respiratory effort; there is no attempt to breathe. This can be a manifestation of a number of disorders, including traumatic brain injury and infectious disorders (including both serious bacterial infections and respiratory diseases such as bronchiolitis and pertussis). Infants with obstructive apnea appear to be attempting to breathe through an occluded airway, with paradoxical movements of the chest and abdomen.12 This is commonly described in upper and lower respiratory tract infections. In cases of oral dysphagia or GERD, infants may exhibit obstructive apnea in relationship to feeds. There can be, at least subjectively, components of both central and obstructive apnea, indicating a mixed picture. Apnea of prematurity is a disorder in the control of breathing in premature infants, occurring in up to 25% of this group.13 Its frequency decreases with increasing maturity, and it is usually outgrown by 37 weeks of postconceptual age.
Skin color change: Episodic changes in infant skin color are often difficult for observers to characterize, particularly in infants with darker skin tones. The color change may be a manifestation of normal infant physiology (e.g., acrocyanosis) or may indicate more serious problems with perfusion or oxygenation (e.g., central cyanosis). Cyanosis becomes apparent when at least 5 grams/100 mL of blood is deoxygenated. Because young infants are often polycythemic, this threshold is more easily met in this age group, and cyanosis may be observed in normal newborns, typically seen in the dense perioral veins. In the distal extremities vasomotor instability can cause acrocyanosis without underlying pathology. Both of these entities are benign. Normal infant polycythemia can also lead to a ruddy appearance (plethoric), which, in the crying infant, may be misinterpreted by lay caregivers as cyanosis or "purple" coloring. For this reason, plethora was not included in definition of BRUE. Pallor is characteristic of the vasovagal response and can be seen in association with gastroesophageal reflux, choking on feeds, or a vagal event.
Tone change: In neonates, changes in muscle tone are difficult to classify because baseline neurologic status varies due to immaturity. Seizures in infants uncommonly present as stereotypical tonic-clonic activity and are more likely to present with altered consciousness or intermittent high and low tone (e.g., infantile spasms). In addition, infants may exhibit changes in tone (either decreased or increased) in the postictal state. Changes in tone may also be secondary to hypoxia resulting from apnea. Stiffening and arching behavior have been well described in infants with gastroesophageal reflux events (Sandifer's syndrome).
Altered responsiveness: An altered level of responsiveness is part of the definition of BRUE because it can be an important component of the event associated with a serious underlying disorder. It was not part of the ALTE definition. Infants may lose consciousness or become unresponsive from a seizure, hypoglycemia, or hypoxemia. However, reports of altered consciousness often represent normal physiology or benign events as well. Because of an immature nervous system, infants may normally appear somnolent, appear unresponsive briefly, or lose consciousness after a breath holding spell.