Sudden Infant Death Syndrome (SIDS)

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Medical Author:

Patrick L. Carolan, MD

Medical Editor:

David Perlstein, MD, MBA, FAAP

David Perlstein, MD, MBA, FAAP

Dr. Perlstein received his Medical Degree from the University of Cincinnati and then completed his internship and residency in pediatrics at The New York Hospital, Cornell medical Center in New York City. After serving an additional year as Chief Pediatric Resident, he worked as a private practitioner and then was appointed Director of Ambulatory Pediatrics at St. Barnabas Hospital in the Bronx.

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Sudden infant death syndrome (also known as SIDS) is defined as the sudden, unexpected death of an infant younger than 1 year of age. If the child's death remains unexplained after a formal investigation into the circumstances of the death (including performance of a complete autopsy, examination of the death scene, and review of the clinical history), the death is then attributed to SIDS. Sudden infant death is a tragic event for any parent or caregiver.

• SIDS is suspected when a previously healthy infant, usually younger than 6 months of age, is found dead following a period of sleep. In most cases, no sign of distress is identifiable. The baby typically feeds normally prior to being placed in for sleep. The infant is then discovered lifeless, without pulse or respiration. Cardiopulmonary resuscitation (CPR) may be initiated at the scene, but evidence shows a lack of beneficial effect from CPR. The cause of death remains unknown despite a careful review of the medical history, scene investigation, and autopsy.



• SIDS is rare during the first month of life. Risk peaks in infants 2-4 months of age and then declines.



• About 90% of SIDS deaths occur in infants younger than 6 months of age.

The cause (or causes) of SIDS is still unknown. Despite the dramatic decrease in the occurrence of SIDS in the United States and worldwide in recent years, SIDS remains one of the leading causes of death during infancy beyond the first 30 days following birth. It is generally accepted that SIDS may be the result of multiple interacting factors.

• Infant development: A leading hypothesis is that SIDS may reflect a delay or abnormality in the development of nerve cells within the brain that are critical to normal heart and lung function. Research examinations of the brainstems of infants who died with a diagnosis of SIDS have revealed a developmental delay in formation and function of several serotonin-binding nerve cell pathways within the brain. These pathways are thought to be crucial to regulating breathing, heart rate, and blood pressure responses during awakening from sleep.



• The hypothesis is that certain infants, for reasons yet to be determined, may experience abnormal or delayed development of specific, critical areas of their brain. This could negatively affect the function and connectivity to regions regulating arousal during sleep.



• 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 (prone) 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 relieve this obstruction.



• Other protective responses to stressful stimuli may be defective in infants who are vulnerable to SIDS. One such reflex is the laryngeal chemoreflex which arises from nerve cell pathways located in the back of the throat (pharynx) and within the voice box (larynx) and upper airway. This reflex regulates 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, triggering swallowing responses which help 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 when infants are in the facedown sleep position.



• Rebreathing stresses: 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, as well as stuffed or plush toys 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.

Even though the specific cause (or causes) of SIDS remains unknown, scientific efforts have eliminated several previously held theories. We now know the following about SIDS:

• Apnea is a term that describes the clinical situation in which a person's breathing stops spontaneously. Apnea associated with prematurity and apnea which occurs during infancy are felt to be clinical conditions that are distinct from SIDS. Infants with apnea may, in some cases, be managed with electronic monitors prescribed by doctors that track heart rate and respiratory activity. Apnea monitors will not prevent SIDS.



• SIDS is neither predictable nor preventable.



• Infants may experience episodes termed apparent life-threatening events (ALTE). These are clinical events in which young infants may experience abrupt changes in breathing, color, or muscle tone. Common causes of ALTE include viral respiratory infections (RSV), gastroesophageal reflux disease, and seizures; however, no definite scientific evidence links ALTE as events that will lead to SIDS.



• SIDS is not caused by immunizations or bad parenting.



• SIDS is not contagious or hereditary.



• SIDS is not anyone's fault.