DESCRIPTION

• Sudden infant death syndrome (SIDS) is the sudden unexpected death of an apparently healthy infant <1 year of age that remains unexplained after a thorough case investigation, including the performance of a complete autopsy with ancillary testing, examination of the death scene, and review of the clinical history.
• SIDS is a subcategory of deaths described as “sudden unexpected deaths in infancy” (SUDI) or “sudden unexpected infant deaths” (SUID).
  • SUID includes diagnoses once considered SIDS, including accidental suffocation in bed or when the cause of death is certified as “undetermined.”
  • When the medical etiology of death is determined by autopsy (e.g., asphyxia, entrapment, trauma [accidental or nonaccidental], cardiac arrhythmia, infection, and metabolic disorders), the cause of death is not considered unexplained.

EPIDEMIOLOGY

• Most common cause of death in postneonatal (1 month to 1 year old) infants
• Peak age of incidence: 1 to 4 months; uncommon before 2 weeks or after 6 months
• Incidence has been decreasing:
  • 1970s: ~2.5 SIDS deaths per 1,000 live births
  • 1980s: ~1.4 per 1,000 live births
  • 1990s: ~1.2 per 1,000 (1992) to 0.7 per 1,000 live births (1999): “Back to Sleep” campaign encouraging supine positioning during sleep in 1994 is associated with a 5-year decline in deaths by half while SUID rates decreased to 0.9.
  • 2000s: Since 1996, actual progress as reflected in SUID rates has stayed relatively flat. In 2019, the SUID rate was 0.91 per 1,000 live births.
• The rates of accidental suffocation and other undetermined or unspecified causes of death have risen.
  • For example, the death rate from accidental suffocation and strangulation in bed (ASSB) increased 7-fold between 1994 and 2013.
  • As a trend, it may be that standardized death scene observations led to the classification of some SIDS deaths as ASSB based on risk factors and not physical evidence of suffocation (known as diagnostic shift).

RISK FACTORS

• Male gender
• Premature birth or low birth weight
• Inadequate prenatal care
• Poverty
• Lower maternal educational level
• Exposure to prenatal, gestational, and postnatal tobacco smoke
• Alcohol and illicit drug use in utero and after infant’s birth
• Maternal substance abuse
• Young maternal age
• Prone and side sleeping position
• Overheating and overbundling
• Soft sleep surface: sofas, couches, and cushioned armchairs are particularly hazardous.
• Soft and loose bedding
• Bed sharing, particularly if sharing bed with one or more smokers; if the infant is <4 months of age (even if neither parent is a smoker); if the infant was born preterm or with low birth weight; if sleeping on a surface with soft bedding; if bed sharing adults have consumed alcohol or drugs; if bed sharing with people who are not the infant’s parents; and if the sleep surface is very soft (couches, armchairs, waterbeds)
• Potential protective factors include the following:
  • Breastfeeding
  • Pacifier use at bedtime and naptime
  • Regular prenatal care
  • Immunizations
  • Room sharing without bed sharing

GENERAL PREVENTION

• Place infants on their backs for every sleep until 1 year of life.
  • Preterm infants should be placed supine as soon as possible.
  • The supine sleep position does not increase the risk of aspiration and choking, even in infants with gastroesophageal reflux.
  • Elevating the head of the crib is not recommended as it may result in the infant sliding to the foot of the bed into a position that may comprise respiration.
  • Side positioning has similar risk as prone positioning and should be avoided.
• Use a firm sleep surface.
• Do not use blankets, pillows, bumper pads, sheepskins, or comforters in the infant’s sleep area.
• Avoid tobacco smoke exposure during pregnancy and after birth.
• Place the infant for sleep on a separate surface designed for infants in the parental room, close to the parental bed.
• Breastfeed as much and as long as possible.
• Consider offering a pacifier at naptime and bedtime. If breastfeeding, wait until breastfeeding is well established before introducing a pacifier. To decrease the risk of strangulation, do not use pacifiers that attach to infant clothing with sleeping infants.
• Do not use alcohol or illicit drugs during pregnancy or after birth.
• Avoid overheating.
• Do not cover infant’s head during sleep.
• Immunize your infant.
• Do not use home cardiorespiratory monitors as a strategy to reduce the risk of SIDS.
• Do not use commercial devices that are inconsistent with safe sleep recommendations.

PATHOPHYSIOLOGY

The “triple risk” model of SIDS describes the interplay of three factors thought to contribute to these deaths: a vulnerable infant, a critical period of development, and modest environmental stressors.

• Individual traits that influence an infant’s vulnerability to SIDS are characterized as intrinsic risk factors. For example, abnormalities in levels of serotonin, serotonin precursors, and/or serotonin receptors are present in the brainstems in up to 70% of SIDS infants at autopsy, suggesting derangements in the neural circuits responsible for arousal and cardiorespiratory functioning.
• Studies have found that 40% of SIDS infants have alterations in the dentate gyrus of the hippocampus elsewhere described in epilepsy.
• The period from birth to age 6 months is one of rapid brain growth and maturation, as well as motor skill acquisition, such as the ability to lift and turn the head in the event of life-threatening rebreathing or asphyxia. The response to hypoxia or hypercarbia occurs as a brainstem reflex, however.
• Exogenous risk factors such as soft bedding, tobacco smoke, side or prone positioning, and overheating may trigger susceptibility in vulnerable infants and provoke terminal pathways of failed autoresuscitation or arousal.
• Failure of arousal in the face of asphyxia or other physiologic disturbances likely contributes to the final pathway leading to these infants’ deaths. Known risk factors for SIDS in the infant’s sleep environment have been linked to arousal and cardiorespiratory responses.
• Prematurely born infants have immature central respiratory responses.
• When compared with supine-sleeping infants, prone-sleeping infants have increased arousal thresholds.
• Prenatal and postnatal nicotine exposure blunts arousal responses to hypoxia.