SIDS Causes

The cause (or causes) of SIDS is still unknown. Despite the dramatic decrease in the incidence of SIDS in the United States in recent years, SIDS remains the number-one cause of death during infancy beyond the first 30 days after birth. It is generally accepted that SIDS may be a reflection of multiple interacting factors.

• Infant development: A leading hypothesis is that SIDS may reflect a delay in the development of nerve cells and nuclei within the brain that are critical to normal heart and lung function. Examinations of the brainstems of infants who died with a diagnosis of SIDS have revealed a developmental delay in formation of a region of the brain known as the arcuate nucleus and related neural pathways of the brain. These pathways are thought to be crucial to regulating breathing and blood pressure responses.
  
  
  • The hypothesis is that certain infants, for reasons yet to be determined, may have a maldevelopment or delay in maturation of certain areas of their brain. This could negatively affect the function and connectivity to regions regulating arousal.
    
    
  • Arousal, in this context, refers to an infant's ability to awaken and/or respond to a variety of physiological stimuli. For example, a child sleeping facedown may move his or her face into such a position so that the nose and mouth are completely obstructed. This may alter the levels of oxygen or carbon dioxide in the infant's blood. Normally, these changes would trigger arousal responses, prompting the infant to move his or her head to the side to alleviate this obstruction.
    
    
  • In addition, other normally protective responses to stressful stimuli may be defective in infants that are vulnerable to SIDS. One such reflex is the laryngeal chemoreflex. This reflex results in changes in breathing, heart rate, and blood pressure when portions of the airway are stimulated by fluids like saliva or regurgitated stomach contents. Having saliva in the airway may activate this reflex, and swallowing may be important to keep the airway clear. When an infant is in the facedown position, the rate of swallowing is decreased. Protective arousal responses to these laryngeal reflexes are also diminished in active sleep in the facedown position.
  
  
• Rebreathing asphyxia: When a baby is facedown, air movement around the mouth may be impaired. This can cause the baby to re-breathe carbon dioxide that the baby has just exhaled. Soft bedding and gas-trapping objects, such as blankets, comforters, waterbeds, and soft mattresses, are other types of sleep surfaces that may impair normal air movement around the baby's mouth and nose when positioned facedown.
  
  
• Hyperthermia (increased temperature): Overdressing, using excessive coverings, or increasing the air temperature may lead to an increased metabolic rate in these infants and eventual loss of breathing control. However, it is unclear whether the increased temperature is an independent factor or if it is just a reflection of the use of more clothing or blankets that may act as objects obstructing the airway.