Episodes of prolonged cessation of breathing or prolonged slowing of heart rate in infants-- believed to be potential signs of risk for SIDS--primarily occur before the developmental age when most SIDS deaths occur, according to a study funded by the National Institute of Child Health and Human Development (NICHD). The findings, appearing in the May 2, 2001, Journal of the American Medical Association, suggest that these events are not necessarily signs of impending SIDS.
"These findings are an important step in understanding SIDS, a mystery that continues to claim children every year," said Duane Alexander, M.D., director of the NICHD. "The NICHD remains committed to solving the mystery of SIDS, and this study helps us to narrow our research focus."
Breathing stoppage, called apnea, and slowed heart rate, called bradycardia, have long been observed in infants at increased risk for SIDS. Researchers have assumed that if such events can be detected, they can also be interrupted, thereby preventing SIDS. The Collaborative Home Infant Monitoring Evaluation (CHIME) study, which used specially designed electronic monitors in the home to detect such cardiorespiratory events in infants, revealed that this assumption might not be true.
"The difference in when extreme events most commonly occur and when SIDS is most likely to occur suggests that these events are not immediate precursors to SIDS, as was once thought," said George Lister, M.D., study group chairman and one of the authors of the JAMA article. "These events might be markers of vulnerability, rather than immediate indicators of SIDS."
The CHIME study followed 1,079 infants during their first six months after birth using electronic home monitors to detect cardiorespiratory events. The infants were classified as either healthy (born at full-term, clinically well, no family history of SIDS in siblings or relatives), or at increased risk of SIDS. The latter group included babies whose risk of SIDS was more than twice their healthy counterparts: preterm or premature babies; siblings of SIDS victims; and those who experienced an apparent life-threatening event (ALTE), defined as an event that required mouth-to-mouth resuscitation or vigorous stimulation.
The home monitors were designed to measure heart rate and breathing patterns including rib cage and abdominal movement and the volume of a breath. Parents were instructed to use the monitors when the baby was sleeping or was not being observed. During 718,358 hours of home monitoring, researchers in the CHIME study found that apnea and bradycardia occurred frequently, even in healthy babies who were born at full-term. However, the most extreme events, those that lasted a very long time by usual medical standards, were common only in infants born prematurely and were found to be associated with significant decreases in blood oxygenation. Moreover, most of these extreme events occurred prior to the age when SIDS is most common (between 2 and 6 months of age for full term infants). Therefore, these results cast serious doubt on the idea that extreme cardiorespiratory events are immediate precursors of SIDS.
In addition, the extreme events were frequently associated with airway obstruction. Home monitors that are currently available for use by parents use methods that would not detect obstructed breathing, which means many of these extreme events might have gone unnoticed.
"Recognizing that there will still be infants who some clinicians wish to have monitored at home, these study results have important implications for future design of such devices," noted Dr. Lister. The findings will also help to determine which infants are at greater risk for extreme events," he added.
Researchers stressed that the CHIME study did not address whether home monitoring decreases the incidence of SIDS, nor did it explore whether extreme cardiorespiratory events are markers of vulnerability to SIDS.
The NICHD is part of the National Institutes of Health, the biomedical research arm of the federal government. The Institute sponsors research on development before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. NICHD publications, as well as information about the Institute, are available from the NICHD Web site, http://www.nichd.nih.gov, or from the NICHD Information Resource Center, 1-800-370-2943;