Sudden Infant Death Syndrome - April 2006
Sudden Infant Death Syndrome (SIDS) remains a nebulous diagnosis in the world of pediatrics, even though it is the most common cause of unexplained infant deaths in Western countries. Through the years, the medical community has made great strides to decrease mortality, but much remains to be elucidated about pathophysiology. The current accepted definition, adopted in 1991, remains, “the sudden death of an infant under 1 year of age, which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history.” Even with this widely accepted diagnosis, there continues to be significant debate and disagreement about the definition of SIDS.
Etiology and Pathogenesis
SIDS is likely a phenomenon with multiple etiologies; no single entity has been found to be a definitive cause. Initial studies describing the pathogenesis not surprisingly involved the nervous system and its effects on respiratory control. Dysregulation of the autonomic nervous system and delayed neuronal maturation of brainstem and central respiratory control centers are at the crux of many theories. Anatomic etiologies such as obstructive sleep apnea (OSA) have also been implicated, not only in the upper airway (positioning of the mandible, oropharynx and tongue) but also in the lower airway (alveolar collapse). Cardiac etiologies revolve around prolonged QT syndrome and rhythm disturbances. Interestingly, there is a 2-3 fold increase in the incidence of SIDS during the winter compared to the summer, regardless of the hemisphere. Thus, infectious theories have been investigated with an association of an increase in the incidence of SIDS with respiratory viral epidemics. This association is even more striking in the presence of other known risk factors for SIDS, such as prone sleeping position and smoke exposure. Investigators believe that there may be a depressed arousability from sleep after a recent viral illness. At the same time, no single infectious agent has been found to be responsible for these findings. Lastly, there are also a myriad of miscellaneous potential etiologies that have not been scientifically confirmed, including mattress toxins, trace metals and immunizations. Homicide as a cause for sudden infant death must be considered, especially if there is a history of multiple cases in the same family.
Risk Factors and Epidemiology
Whereas the etiologies of SIDS remain largely elusive, risk factors have been more concretely identified over the past several decades. These risk factors include: male gender, prematurity and/or low birth weight, maternal smoking, seasonal predilection (winter), lack of prenatal care, low maternal age, higher parity, single parenthood and multiple gestation. Additional risk factors include unsafe sleeping conditions including prone position, soft bedding and sleeping with potentially obstructive materials (toys, stuffed animals and waterbeds). In fact, maternal smoking is the highest modifiable risk factor while prone sleeping is a major preventable risk factor in SIDS. Epidemiologically, SIDS is clearly more common in “chaotic” households with lower educational and socioeconomic status. SIDS seems to be rare in Asian communities and much higher in African-American populations, compared to Caucasian populations. Acute Life Threatening Events (ALTE) have not been shown to consistently correlate with SIDS. In fact, most infants who die of SIDS do not have a preceding ALTE.
Interventions
In 1992, the American Academy of Pediatrics (AAP) introduced the “Back to Sleep” campaign in order to take advantage of preventable risk associated with prone sleeping. This has certainly contributed to the 50% decrease in SIDS seen over the last 10 years. Even with the “Back to Sleep” campaign, parents have continued to practice prone sleeping secondary to cultural norms. Community concerns for fever, stuffy nose and trouble sleeping have been strong regarding the supine sleeping position. Community education and prevention can be instrumental in bridging these cultural norms. Latin and African-American communities have a higher rate of prone sleeping and sleeping with soft and potentially obstructive bedding. In Chicago, through a vigorous public campaign and outreach, there was a marked decrease in the incidence of SIDS in these populations. Furthermore, the complaints of fever, stuffy nose and trouble sleeping were actually decreased in infants in the supine sleeping position. Strong proponents of the supine sleeping position have also suggested swaddling infants to prevent them from rolling over prone. In recent years, breastfeeding and pacifier use have been found to provide possible protective effects against SIDS. The mechanism of these effects remains unclear but experts believe that these practices decrease the risk of obstructing the nose and mouth.
Home monitoring deserves special mention. Extensive research has shown that apnea or bradycardia have no causative effect on SIDS. Furthermore, epidemiologic studies have failed to show any impact of home cardio-respiratory monitoring for apnea and/or bradycardia on the incidence of SIDS. The AAP strongly recommends that home monitoring should not be used in the prevention of SIDS. Note that the use of home cardio-respiratory monitoring may be warranted in certain groups of infants including: preterm infants with extreme apnea, infants with airway abnormalities or who are technologically dependent, infants with rare medical disorders affecting respiratory control and infants with chronic lung disease.
Outlook
Making a diagnosis of SIDS has been difficult, especially with the lack of proper investigations in the past. As such, organizations have focused on protocols to ensure that specific standardized steps are taken to make an accurate diagnosis of SIDS and to attempt to determine its etiology. Pediatricians should focus on prevention and diagnosis. Through current knowledge of risk factors and educating the families and communities we serve, perhaps we can contribute further to the decline of SIDS.
References
1. Byard RW, Krous HF: Sudden Infant Death Syndrome: Overview and Update. Pediatr Dev Pathol. 2003, 6(2):112-27.
2. Daley KC: Update on sudden infant death syndrome. Curr Opin Pediatr. 2004, 16:227-232.
3. Guntheroth WG, Spiers PS: Infant sleeping position and sudden infant death syndrome: a systematic review. Int J Epidemiol. 2005, 34(5):1165-6.
4. Shoemaker M, Ellis M et al: Should home apnea monitoring be recommended to prevent SIDS? J Fam Pract. 2004, 53(5): 418-419.
5. Spitzer AR: Current controversies in the pathophysiology and prevention of the sudden infant death syndrome. Curr Opin Pediatr. 2005, 17:181-185.
This information provided by Eric Zee, M.D.
Division of Pediatric Pulmonary & Cystic Fibrosis
(510) 428-3305