Apnea Classification in Preterm Infants
The recurrent apneic episodes lasting more than 20 seconds and occurring multiple times per hour in this preterm infant most likely represent mixed apnea (Answer C), as this is the predominant type in clinically significant apnea of prematurity, particularly for prolonged episodes. 1, 2
Understanding Apnea Types in Preterm Infants
The classification of apnea in preterm infants is based on the presence or absence of respiratory effort during the apneic episode:
- Central apnea shows complete absence of respiratory effort with no thoracoabdominal movements during the apneic episode 1, 3
- Obstructive apnea demonstrates continued or paradoxical respiratory effort despite absent airflow, often with thoracoabdominal paradox 1, 4
- Mixed apnea is characterized by an initial central component (no respiratory effort) followed by obstructive breathing efforts against a closed airway 1, 2
Why Mixed Apnea is Most Likely
The duration and frequency of episodes in this case strongly suggest mixed apnea as the predominant type. Research demonstrates that as apnea duration increases beyond 20 seconds, the proportion of mixed apnea episodes increases dramatically from 20% to 60%, while purely central apnea decreases from 69% to 29% 2. In a study of 1,520 apneic episodes in preterm infants:
- Episodes lasting 10-14 seconds: 69% central, 20% mixed 2
- Episodes lasting >20 seconds: 29% central, 60% mixed 2
Multiple episodes per hour occurring repeatedly indicates clinically significant apnea of prematurity, which is almost universal in infants <1000g at birth and affects >50% of all premature infants. 5
Clinical Significance and Pathophysiology
The recurrent nature and prolonged duration (>20 seconds) meet the definition of clinically significant apnea, which is defined as breathing pauses lasting >20 seconds or >10 seconds if associated with bradycardia or oxygen desaturation 5.
Mixed apnea in preterm infants reflects the "physiologic" immaturity of respiratory control combined with upper airway obstruction. 3 The pathophysiology involves:
- Altered ventilatory responses to hypoxia and hypercapnia 3
- Laryngeal chemoreflex sensitivity 3
- Pharyngeal airway collapse during the obstructive component 4
Treatment Implications Based on Apnea Type
Understanding the apnea type is critical because treatment differs:
- For obstructive/mixed components: CPAP or nasal intermittent positive pressure ventilation markedly decreases mixed and obstructive apnea (p<0.01 and p<0.03 respectively) by splinting the pharyngeal airway 4
- For central components: Methylxanthine therapy (caffeine citrate) is the mainstay, with a loading dose of 20 mg/kg followed by 5 mg/kg daily maintenance 6, 3
- Central apnea is entirely unaffected by CPAP, making accurate classification essential 4
Common Pitfalls
Do not assume all apnea in preterm infants is purely central. While 69% of brief episodes (10-14 seconds) are central, the majority of prolonged, clinically significant episodes (>20 seconds) are mixed in type 2. Infants with prolonged obstructive or mixed apnea have higher rates of intraventricular hemorrhage, hydrocephalus, and abnormal neurological development compared to those with purely central apnea 2.
Prone positioning should be used for obstructive components during monitored NICU care, as it helps prevent pharyngeal collapse and alveolar atelectasis, though this is only appropriate in the controlled NICU environment 3.