Apnea of Prematurity (AOP) is a common condition in preterm neonates characterized by the cessation of breathing for at least 20 seconds, often accompanied by bradycardia and/or desaturation. This is most common in neonates born at <34 weeks of gestation, as their respiratory control system is immature. Below is a detailed explanation and classification of AOP:
Pathophysiology of Apnea of Prematurity
- Immature Respiratory Centers:
- The brainstem’s respiratory centers (medulla and pons) are underdeveloped in preterm infants, leading to poor integration of sensory inputs for breathing regulation.
- Chemoreceptor Dysfunction:
- Immature central and peripheral chemoreceptors respond less effectively to changes in oxygen (hypoxia) and carbon dioxide (hypercapnia) levels.
- Reduced Respiratory Muscle Tone:
- The diaphragm and intercostal muscles are underdeveloped, leading to ineffective breathing efforts.
- Increased Vulnerability to Hypoxia:
- Preterm neonates have higher oxygen consumption and reduced oxygen stores due to smaller functional residual capacity and immature lungs.
- Immature Reflex Mechanisms:
- Reflexes such as the laryngeal chemoreflex, which prevents aspiration, may inhibit breathing in response to stimulation.
Classification of Apnea
- Central Apnea:
- Complete cessation of respiratory effort due to failure of the brainstem to initiate breathing.
- Obstructive Apnea:
- Airway obstruction prevents airflow despite respiratory effort.
- Mixed Apnea:
- A combination of central and obstructive apnea, most common in neonates.
Causes of Apnea
Primary Cause:
- Immaturity of the central nervous system in preterm neonates.
Secondary Causes:
- Infections:
- Sepsis, meningitis, pneumonia.
- Respiratory Disorders:
- Respiratory distress syndrome (RDS), transient tachypnea of the newborn (TTN), meconium aspiration syndrome (MAS).
- Metabolic Disturbances:
- Hypoglycemia, hypocalcemia, metabolic acidosis.
- Neurological Disorders:
- Intraventricular hemorrhage (IVH), seizures, periventricular leukomalacia (PVL).
- Environmental Factors:
- Hypothermia, hyperthermia, excessive handling, or stress.
Management of Apnea of Prematurity
- Supportive Care:
- Ensure a neutral thermal environment to reduce energy expenditure.
- Gentle handling to minimize stimulation-induced apnea.
- Monitoring:
- Continuous cardiorespiratory and oxygen saturation monitoring.
- Pharmacological Management:
- Caffeine Citrate:
- Most effective treatment.
- Mechanism: Stimulates the respiratory center, increases diaphragm contractility, and reduces apnea frequency.
- Dose: Loading dose 20 mg/kg, maintenance dose 5-10 mg/kg/day.
- Theophylline may be used as an alternative but is less preferred due to a narrower therapeutic range.
- Ventilatory Support:
- Nasal Continuous Positive Airway Pressure (nCPAP):
- Keeps the airway open and reduces obstructive apnea.
- Mechanical Ventilation:
- Used for severe or recurrent apnea unresponsive to other treatments.
- Treat Underlying Causes:
- Address sepsis, metabolic abnormalities, or other secondary causes as appropriate.
- Weaning:
- Apnea episodes usually resolve by 34-36 weeks postmenstrual age. Caffeine is discontinued once the infant remains apnea-free for 5-7 days.
Prognosis
- Most infants outgrow AOP as their respiratory system matures.
- Long-term outcomes are generally favorable, although severe, recurrent apnea may be associated with neurodevelopmental delays.
Reference:
Cloherty JP, Eichenwald EC, Hansen AR, Stark AR. Manual of Neonatal Care, 8th Edition.