Apnea of Prematurity: Mixed Apnea is Most Common
In preterm infants with recurrent apneic episodes lasting more than 15 seconds and occurring multiple times per hour, the answer is C) Mixed apnea, as this represents the predominant pattern in apnea of prematurity.
Understanding Apnea Types in Preterm Infants
Mixed Apnea Predominates in Preterm Infants
Mixed apnea accounts for approximately 88% of apneic episodes in preterm infants, consisting of a central component (cessation of respiratory drive) followed by an obstructive component (upper airway closure) 1
The typical sequence involves initial central apnea followed by airway obstruction, with the majority (76%) occurring without any respiratory effort, suggesting that diaphragmatic action is not necessary to occlude the airway 1
In a study of 198 mixed apnea episodes in 33 preterm infants, the distribution by duration was: 20 episodes <5 seconds, 78 episodes 5-10 seconds, 45 episodes 10-15 seconds, 27 episodes 15-20 seconds, and 28 episodes ≥20 seconds 1
Clinical Definition and Significance
Clinically significant apnea in preterm infants is defined as breathing pauses lasting >20 seconds, or >10 seconds if associated with bradycardia or oxygen desaturation 2
Apnea of prematurity affects >50% of premature infants and is almost universal in infants <1000g at birth 2
Among preterm neonates with multiple apneic episodes, 58% died in one large prospective study, compared to only 6% without recorded apnea, highlighting the clinical significance 3
Why Not Pure Central or Obstructive?
Pure central apnea alone is less common because the loss of upper airway tone that accompanies cessation of central respiratory drive typically leads to subsequent airway collapse, creating the mixed pattern 1
Pure obstructive apnea without a preceding central component is uncommon in preterm infants, as the mechanism typically begins with loss of central drive 1, 4
Spontaneous neck flexion can contribute to airway obstruction during apneic spells, with 36 of 43 observed spells being mixed in nature 4
Pathophysiologic Mechanism
The mechanism for airway closure in mixed apneas is most likely a lack of upper airway tone, which normally occurs with cessation of central drive to breathe 1
Respiratory efforts never preceded airway occlusion in the studied episodes, supporting the sequence of central apnea followed by passive airway collapse 1
In some cases, transient upper airway obstruction following brief periods of sleep apnea can produce sudden and severe bradycardia 5
Clinical Pitfall to Avoid
Do not assume all apnea in preterm infants is purely central - the mixed pattern is the rule rather than the exception, which has implications for monitoring and intervention strategies 1, 4
The term "primary apnea" (option D) is not a recognized classification in the context of recurrent apnea of prematurity and typically refers to the initial apnea occurring immediately after birth asphyxia, making it an incorrect choice for this clinical scenario 2