|The Sudden Infant Death Syndrome Alliance||1314 Bedford Avenue
Baltimore, MD 21208
TO: SIDS Alliance Affiliate Presidents and Executive
FROM: Phipps Cohe, National Public Affairs Director
RE: EFFECTS OF REDUCTIONS TO AN INFANT'S OXYGEN SUPPLY EXAMINED IN NEW BRITISH STUDY; SPECULATION ON A POSSIBLE LINK BETWEEN HIGH ALTITUDE AND SIDS STIRS PARENTAL TURBULENCE OVER AIR TRAVEL
In the March 21, 1998 issue of the British Medical Journal, researchers at North Staffordshire Hospital Centre, Stoke on Trent, England, reported on their examination of healthy infants' response when subjected to airway hypoxia (reduced oxygen supply). The authors based their study on the premise that "a reduction in the partial pressure of inspired oxygen may increase the risk of apparent life threatening events and sudden death in infancy" for some infants.
The research group, led by David Southall, MD, examined effects of 15% exposure to oxygen (a 6% reduction in oxygen from normal levels) among a carefully watched study group of 34 infants, 13 of whom were SIDS siblings. This reduced level was intended to simulate the oxygen levels experienced by infants during routine air travel or at mountain altitudes during vacations. Blood oxygen levels were maintained at slightly reduced rates in most of the infants and no ill effects were noted either during the challenge or for the two days the infants were retained in the hospital after their oxygen levels were returned to normal. Exposure to hypoxia was, however, ended early for 6 of the infants; 4 of whom exhibited severe, potentially dangerous drops in blood oxygen levels. None of the infants died during the course of the study.
The most frequent cause of airway hypoxia in infants is respiratory infection, which has been linked scientifically to life-threatening hypoxic episodes and sudden infant death syndrome in a small proportion of infants. The degree of airway hypoxia that is safe for infants to be exposed to is unknown, although one U.S. scientist reported no ill effects in his studies on infants with airway hypoxia at 25% exposure to oxygen--a reduction in oxygen levels beyond that which Dr. Southall has examined.
Dr. Southall became interested in studying the effects of airway hypoxia on infants after two families attending their outpatient clinic said their babies had died of SIDS within 24 hours following intercontinental flights. The families of the 4 infants who experienced severe drops in blood oxygen levels and were taken off the study early were advised against taking their infants on an airplane or to high altitude until the infants were older.
According to Carl E. Hunt, MD, "There has never been any evidence of an association between high altitude and risk for SIDS. There are no reported cases of SIDS occurring during flights. Although there have been some cases of SIDS in the 1 to 2 days following a flight, there is no physiologic reason to make a connection between these two occurrences. Whatever problem might exist in flight would progressively improve as soon as descent begins. Accordingly, this study does not provide any new information that should change any established recommendations regarding infant care in general or air traffic in specific. Also of importance, the risk of SIDS for infants living at higher altitude has been studied, and no relationship has been found."
The findings by Dr. Southall are consistent with numerous prior studies over the past 10 to 15 years indicating that babies at increased risk for SIDS, as a group, have decreased ability during sleep to arouse to a low oxygen challenge. Dr. Hunt concludes that the hypothesis that failure to recognize and respond to low oxygen levels may be an important risk factor for SIDS.
1.) While it is meaningful to study research topics such as airway hypoxia, it is important to keep in mind that the cause(s) of SIDS remain unknown. Airway hypoxia has not yet been established as a risk factor, however, an infant's failure to recognize and respond to low oxygen levels appears to be a significant consideration for SIDS.
2.) The degree of airway hypoxia that is safe for infants to be exposed to is unknown. While the finding that some babies react more dramatically than others to a drop in oxygen seems significant, the sample size is small and additional research is needed before any conclusions can be drawn. Therefore, it is presumptive to suggest that there may be any danger to infants presented by oxygen levels associated with either air travel or visits to mountain areas.
3.) In his study, Dr. Southall mentions his concern regarding two cases of SIDS following air travel, yet the 4 infants suffering severe drops in blood oxygen levels during his study were released from the hospital within 2 days and no information was provided regarding any possible lingering effects. There is some information available through the Colorado SIDS Program on infants who died following flights while on vacation at mountain altitudes to which they may not have been accustomed--however, these cases are few, with 0 to 2 SIDS deaths recorded for out-of-state visitors to Colorado each year over the past 7 years.
4.) British Airways, which transports over 34 million passengers a year, reports that no cases of SIDS have been recorded during flight. The Air Medical Research Division of the Federal Aviation Administration also reports no cases of SIDS deaths on board domestic or transcontinental carriers, albeit estimates that 40,000 children under the age of 2 travel by airplane in the U.S. each day (20,000 flights per day, 2 children per flight). Given the thousands of infants who fly every year and thrive, parents should refrain from concluding that air travel with their baby may have caused or contributed to their infant's SIDS death.
Ronald M. Harper, PhD
UCLA Brain Research Institute
Thomas Keens, MD
Childrens Hospital of Los Angeles
Carl E. Hunt, MD
Bradley Thach, MD
Medical College of Ohio
Washington University School of Medicine
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