CHICAGO-- Although the incidence of sudden infant death syndrome (SIDS) has dropped more than 40% since 1992, when the American Academy of Pediatrics (AAP) began to recommend placing infants in the supine sleep position, the decline in the death rate has leveled off. Furthermore, SIDS remains the leading cause of infant death in the United States.

These findings were released by the AAP's Task Force on Infant Sleep Position and Sudden Infant Death Syndrome, which recently published an update on SIDS prevention.[1] With its report, the AAP Task Force seeks to help physicians further reduce the incidence of SIDS by expanding its earlier infant sleep recommendations, urging more intense education for high-risk populations, and reviewing the factors that put infants at risk for SIDS.

HIGH RATE AMONG BLACK INFANTS

One reason the decline in the SIDS death rate may have ceased is that some segments of the population aren't getting adequate information about prevention--"particularly blacks, who have three times the SIDS rate of whites," explained AAP Task Force chair John Kattwinkel, MD, in an interview with RESPIRATORY REVIEWS. He recommends that the national Back to Sleep campaign and other SIDS prevention efforts be targeted more toward blacks, one third of whom still put their infants to sleep in the prone position.[2]

"The rate of prone placement in the overall population is now a little bit less than 20%," reported Michael Malloy, MD, who is an AAP Task Force member and a professor of pediatrics at the University of Texas Medical Branch in Galveston.

Of course, physicians should continue to inform parents about the importance of the supine sleep position in SIDS prevention. Whenever possible, they should also educate daycare providers, grandparents, and others who care for infants.

"Some mothers are so concerned about SIDS that they never put their babies on their stomach," said Dr. Kattwinkel, a professor of pediatrics at the University of Virginia in Charlottesville. However, some prone positioning is important for infants to develop shoulder-girdle strength and avoid occipital plagiocephaly. Prone positioning is appropriate when infants are awake and observed.

No evidence exists that nonprone sleep positions increase infants' risk of death from aspiration, as some physicians initially feared. However, these sleep positions may be associated with a greater incidence of gastroesophageal reflux and a slight delay in the attainment of gross motor milestones. The latter difference is undetectable by 18 months of age, however.

REBREATHING AND PRONE SLEEP

The mechanism underlying SIDS is unknown, explained Dr. Kattwinkel. "However, there are data suggesting that rebreathing may be a factor," he said.[3] These data include pathologic evidence of arcuate nucleus immaturity in SIDS cases. The arcuate nucleus is a brainstem region believed to be responsible for respiratory control and arousal from sleep.

"The theory is that if babies with an immature arcuate nucleus get in a compromising position, such as having their faces burrowed in soft mattresses or pillows, they keep rebreathing and die rather than wake up positions," said Dr. Kattwinkel. Prone positioning on soft sleeping surfaces and covering the head are thought to facilitate rebreathing, which leads to hypoxia and hypercapnia.

Devices to prevent rebreathing and maintain a nonprone sleep position are available. They are not recommended, however, because they have not been tested sufficiently to demonstrate safety or efficacy.

Prone sleep--perhaps the most notorious SIDS risk factor--multiplies the likelihood of SIDS 1.7 to 12.9 times. However, even side sleeping carries a slightly higher SIDS risk than supine sleep does, perhaps because infants can more easily roll into the prone position. Thus, in a revision to its 1992 recommendation to put infants to sleep in any nonprone position, the AAP now advises the supine sleep position for optimum risk reduction.

About 20% of caregivers switch their infants from nonprone to prone sleep positions at 1 to 3 months of age. This is dangerous because SIDS is most likely to occur between those ages. Evidence also exists that infants accustomed to supine sleep are at especially high risk for SIDS when switched to prone sleep positions.[4]

OTHER SIDS RISK FACTORS

Pillows, quilts, comforters, sheepskins, waterbeds, sofas, and other types of soft bedding and sleeping surfaces markedly increase SIDS risk; this is most likely because of their association with rebreathing. Stuffed toys and other soft objects also raise the risk of SIDS. For optimum safety, parents should not put these things in their infant's sleep environment. If parents insist on providing some type of covering, they should tuck in a blanket around the crib mattress to prevent the infant's face from being covered. Or they can dress the infant in bed clothing. Any cribs that are used should conform to the safety standards of the Consumer Product Safety Commission and the American Society for Testing and Materials.

Bed sharing may be hazardous under certain conditions, especially if the adult is sedated from drug or alcohol use. "Adult beds may also be dangerous because the infant could roll between the headboard and the mattress and become entrapped," Dr. Malloy added. An alternative to bed sharing may be to place the infant's crib near the caregiver's bed to facilitate breast-feeding and other types of contact.

"Smoking has been observed to increase the risk of SIDS by about twofold in studies from the mid-1980s to the present," Dr. Malloy told RESPIRATORY REVIEWS. "The mechanism by which smoking contributes to SIDS remains unknown. But we certainly encourage parents not to smoke in an infant's immediate environment."

Overheating is a SIDS risk factor associated with too much bed clothing or coverings and a high room temperature. To minimize this risk, parents should put their infant to sleep in light clothing, keep the room temperature comfortable for a lightly clothed adult, and make sure the infant doesn't feel hot to the touch.

Premature and low-birth-weight infants are at increased risk of SIDS, although the mechanisms in these infants are unclear. These infants should receive the same SIDS prevention strategies as full-term infants.

Electronic respiratory and cardiac monitors for home use may be of value for infants with extreme cardiorespiratory instability. However, there are no data showing that home monitoring lowers SIDS incidence, the Task Force acknowledged.

--Timothy Begany

References
1. Task Force on Infant Sleep Position and Sudden Infant Death Syndrome. Changing concepts of sudden infant death syndrome: implications for infant sleeping environment and sleep position (RE9946). Pediatrics. 2000;105:650-656.
2. Willinger M, Ko CW, Hoffman HJ, et al. Factors associated with caregivers' choice of infant sleep position, 1994-1998: the National Infant Sleep Position Study. JAMA. 2000;283:2135-2142.
3. Kinney HC, Filiano JJ, Sleeper LA, et al. Decreased muscarinic receptor binding in the arcuate nucleus in sudden infant death syndrome. Science. 1995;269:1446-1450.
4. Mitchell EA, Thach BT, Thompson JM, Williams S. Changing infant's sleep position increases risk of sudden infant death syndrome. New Zealand Cot Death Study. Arch Pediatr Adolesc Med. 1999;153:1136-1141.