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  • Updated 05.08.2022
  • Released 02.13.1995
  • Expires For CME 05.08.2025

Sudden infant death syndrome



Sudden infant death syndrome (SIDS) is the sudden, unexpected death of an infant (< 1 year old) that is unexplained by careful review of history, autopsy, and death scene investigation. SIDS is a subcategory of sudden unexpected infant death (SUID), a term used to designate any unexpected death without an obvious cause that occurs in children before 1 year of age. Besides SIDS, SUID includes other conditions such as asphyxia, arrhythmias, and accidental trauma. SIDS is a leading cause of death in infants younger than 1 year of age. Ninety percent of SIDS cases occur before 6 months of age. The exact etiology of SIDS is not known, but generally the triple-risk model is the most accepted hypothesis. This model proposes that SIDS is caused by the interplay between risk factors from 3 areas: 1) a specific and/or critical period of development, 2) an infant’s underlying vulnerability, and 3) an environmental trigger. Accordingly, risk factors and protective factors have been identified and contribute to the current recommendations directed at prevention of SIDS. In this article, the authors discuss the clinical presentation, pathophysiology, diagnostic workup, and current recommendations for SIDS (68).

Key points

• By definition, sudden infant death syndrome (SIDS) is of unknown cause and is a diagnosis of exclusion (unexplained after review of history, autopsy, and death scene investigation); if evidence of a specific cause of death is found, then it is not SIDS.

• Sudden unexpected infant death (SUID) is a term that includes unexpected deaths in infants younger than 1 year of age that fit various categories (eg, SIDS, asphyxia, arrhythmias, accidental trauma).

• SIDS affects infants less than 12 months of age, peaks between 2 to 4 months, and is less common after 6 months of age. SIDS is more common in boys and African Americans.

• The etiology of SIDS is unknown but is thought to be associated with autonomic nervous system dysregulation and impaired arousal mechanisms.

• Preventative measures include sleeping on the back; sleeping on a firm surface without extraneous soft bedding, clothing, toys, or positioning devices; breastfeeding; room sharing with parents, but not bed sharing; avoiding excessive room heat; avoiding exposure to cigarette smoke, alcohol, and drugs during pregnancy and after birth; and the use of pacifiers.

Historical note and terminology

Sudden infant death syndrome (SIDS) has been postulated to have existed from prehistoric times (40). The first recorded case that could be considered SIDS appears to have been an infant in the Old Testament (Bible: 1 Kings 3:19), though the infant’s death was attributed to suffocation from overlying by its mother. To this day, distinguishing between accidental or intentional suffocation and SIDS in the absence of overt signs of physical violence proves difficult. In 19th-century Germany, pathologists invented an explanation that would defend mothers and nursemaids from accusations of either overlying or infanticide. Initially, they blamed enlargement of the thymus for directly suffocating the infant, failing to recognize that the thymus is typically large in infancy (39). Later pathologists theorized that sudden death was caused by status thymicolymphaticus, a fictional constitutional disorder associated with alleged hyperplasia of the thymus, but did not specify any measurements.

At the Second International Conference on Causes of Sudden Death in Infants in 1969, a definition of SIDS was proposed by Beckwith as “the sudden death of any infant or young child which is unexpected by history, and in which a thorough postmortem examination fails to demonstrate an adequate cause of death” (07). This definition was further refined in 1989 by an expert panel with the National Institute of Child Health and Human Development to specify age less than 1 year old and include death scene investigation. Some have recommended exclusion of the diagnosis of SIDS if the death scene has not been visited, but that alone should not exclude the diagnosis of SIDS because it would exclude half of all probable cases (45). A new definition of SIDS, “the San Diego classification,” was proposed in 2004 and introduced subcategories for SIDS cases; however, it has not been universally accepted, and adjustment of the definition has been suggested (51). The necessity of a universally accepted definition is evident when considering the results of a national survey of medical examiners and coroners, in which they did not universally agree on the classification of death when given 4 different case scenarios of SIDS (89).

The term “sudden unexpected infant death” (SUID) has emerged to include all cases of unexplained sudden and unexpected deaths in infants younger than 1 year old. This is an umbrella term that encompasses SIDS, suffocation, trauma, asphyxia, entrapment, arrhythmia, and metabolic conditions, among other causes of death (68).

For years, “apparent life-threatening event” (ALTE) was used to describe events that were frightening to the observer, which typically included presentation of apnea, color change, and marked change in muscle tone. In ALTE, the observer frequently feared that the infant could die or had died. In the past, ALTE was termed “near-miss SIDS.” However, evidence supports that fact that ALTE and SIDS are different and that ALTE does not increase the risk for SIDS. As such, the near-miss SIDS term is no longer used. Furthermore, children presenting with ALTE were ultimately found to have an underlying condition in 50% of cases. It is important to remember that ALTE is a subjective observer-experienced event (18).

In 2016, the term “brief resolved unexplained event” (BRUE) was introduced and recommended to be used instead of ALTE in infants with no explanation for the event after a history and physical exam, thereby adding the objective clinical exam to the definition. BRUE is defined as an episode occurring in an infant younger than 12 months and reported by the observer as brief (less than 1 minute) and now resolved (infant back to baseline), with normal vital signs, history, and physical examination at the time of assessment by a medical provider. If the observed episode does not fit the criteria for this definition, the guideline recommends further investigation. Infants with BRUE need to be risk stratified into low risk and high risk. The following characteristics identify low risk according to published guidelines: infants older than 60 days, gestational age more than 32 weeks, and postconceptional age more than 45 weeks; no history of prior BRUE; event duration of less than 1 minute; CPR was not required; and no concerning history or physical exam findings. High-risk infants with BRUE include infants younger than 2 months with recurrent episodes, unstable vital signs, abnormal history or physical exam findings, and a prolonged event or event requiring cardiopulmonary resuscitation (102).

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