Tuesday October 7 2008
New research suggests, “keeping a fan on while a baby sleeps could dramatically cut the risk of cot death”, the Daily Mail reports. It said that the study looked at the sleeping conditions of babies who had died from Sudden Infant Death Syndrome (SIDS) and found that keeping a fan on reduced the risk of SIDS by 72% compared to not doing so. Specific risk factors for SIDS were also reduced, with a 94% reduction in rooms with temperatures over 21°C, 85% in rooms with the windows shut, and 88% in babies who didn’t use pacifiers while sleeping.
This study was well-conducted, but does have some limitations. It is also important to note that fans had little or no effect when other sleeping conditions were good, such as in cooler rooms (21°C or lower), where there was already a window open, where the infant was sleeping on their back, had a pacifier, or was not sharing a bed with a non-parent. As The Foundation for the Study of Infant Deaths suggests, if these conditions are adhered to, using a fan may not bring additional benefit. Parents who are concerned about the risk of SIDS could consider using a fan in warm rooms, but this should be used together with other steps known to reduce risk.
Where did the story come from?
Dr Kimberley Coleman-Phox and colleagues from Kaiser Permanente and the University of California carried out this research. The study was funded by the National Institute of Child Health and Human Development, the National Institute on Deafness and Other Communication Disorders, and a Kaiser CHR Fellowship. The study was published in the peer-reviewed medical journal, Archives of Pediatric and Adolescent Medicine.
What kind of scientific study was this?
The aim of this case control study was to investigate whether the ventilation (fans or open windows) in babies’ rooms is related to the risk of Sudden Infant Death Syndrome (SIDS). The researchers were interested in investigating this because some studies have suggested that one way SIDS might occur is by babies rebreathing exhaled air (which contains high levels of carbon dioxide) trapped in bedding. If this is the case, ventilation might increase air circulation around the baby’s nose and mouth, reducing the risk of rebreathing.
Using medical records, the researchers identified all babies who had died from SIDS (cases) in 11 counties in California between May 1997 and April 2000. Mothers who spoke English or Spanish were sent letters to explain the study, and asked if they would like to participate. Those who agreed to participate were then interviewed on the phone or in person. Of the 396 eligible cases, 185 had contactable biological mothers who agreed to participate and give a complete interview.
The researchers also identified possible controls using birth certificates, and matched them to cases in terms of age, maternal ethnicity/race, and which county they lived in. The controls were then randomly compared to those cases with completed maternal interviews. Mothers of 312 control infants completed interviews.
Mothers of cases completed the interview an average (median) of 3.8 months after their baby died. All maternal interviews were conducted by people trained in SIDS grief counselling. Mothers of cases and controls were asked about possible confounding factors such as sociodemographic features, maternal prenatal medical history, and infant medical history. They were also asked about their infant’s sleeping conditions at the ‘last sleep’, including whether there was a fan in the room or a window was left open, sleep surface, room temperature, and type of bedding used.
The researchers then looked at whether ventilation was more or less common among babies who had died of SIDS than those who had not. They took into account (adjusted for)potential confounding factors in their analyses. They also looked at whether the effect of room ventilation differed in different sleep conditions (e.g. different room temperatures, sleep positions, etc.)
What were the results of the study?
The researchers found that cases and controls differed in certain characteristics. The mothers of cases were more likely than the mothers of controls to be smokers, to have started their prenatal care after the first three months of their pregnancy, to have had more than one child, to be unmarried, and to be under the age of 25.
The cases were more likely than controls to have been preterm births, to have had a low birth weight (less than 2500g), to have lived in a home where there was regular smoking inside the house, and to have had a fever in the 48 hours before their last sleep. In their last sleep, cases were more likely than controls to be placed on their sides or stomachs, to have not used a pacifier, to have slept on a soft surface, to have shared their bed with someone other than their parent, and to have ended up with bedding or clothing covering their heads.
Although sleeping in a room with the window open was less common in cases than controls, this difference did not reach statistical significance (16% of cases compared to 24.9% of controls, adjusted odds ratio 0.64, 95% CI 0.33 to 1.21).
Among the 185 cases, six had slept with a fan on in their room (3.6%) compared to 36 of the 312 controls (11.7%). Sleeping with a fan on was associated with a 72% reduction in the odds of having SIDS after adjustment (taking into account potential confounding factors - odds ratio 0.28, 95% confidence interval [CI] 0.10 to 0.77). The effect of having a fan on was significantly greater in warmer rooms (above 21°C) than in colder rooms. There was a trend for a greater effect of fans in rooms where windows were kept closed, for infants who slept on their stomach or side, shared a bed with someone other than a parent, and who did not use a pacifier. However, these differences were not statistically significant.
What interpretations did the researchers draw from these results?
The researchers concluded that fans may reduce the risk of SIDS in children who sleep in environments in which the rebreathing of exhaled air is easier.
What does the NHS Knowledge Service make of this study?
There are a few points to note when interpreting this study:
- As with all studies of this type, there may be differences between cases and controls other than the factor of interest that may be responsible for the results. There were differences between cases and controls in known risk factors for SIDS, such as smoking in the home, and the researchers attempted to control for these factors in their analyses, which increases the confidence that can be had in the results. However, there may still be some residual effect of these or other factors.
- This type of study relies on the participants recalling past situations, and these memories may not be accurate. The mothers of infants who died of SIDS were recalling events that had occurred between one and 20 months previously (median 3.8 months), while mothers of controls were recalling their child’s sleeping environment on the previous night. This may have lead to systematic differences in the accuracy of their recall. The authors felt that this was unlikely, as mothers of cases reported similar levels of fan use regardless of the time since their child’s death. In addition, the trauma associated with their infant’s death may have affected the mothers’ memories of the events. Ideally, the benefits of fans should be assessed in a prospective study, which would avoid these problems.
- In addition, quite a large number of those who were asked to participate declined (50% of eligible cases and 59% of eligible controls). If those who chose to participate differed from those who did not, this could have led to inaccurate results. However, the authors suggested this had not happened, and said that by comparing those who chose to participate to the entire eligible population (using birth certificate data), they found estimates of SIDS risk with factors such as maternal age to be similar.
- Parents should note that the effect of a fan was smaller when children were in “lower risk” sleep environments, for example, when the room was cooler (21°C or lower), where there was already a window open, where the infant was sleeping on their back, had a pacifier, or was not sharing a bed with a non-parent. If these conditions are adhered to (e.g. by keeping rooms below 21°C), adding a fan may not bring additional benefit.
- The researchers did not analyse the effect of fan use according to whether the mother smoked in pregnancy, or whether there was regular smoking in the home after the birth. Compared to the controls, almost twice as many mothers of SIDS cases smoked during pregnancy, suggesting that this was an important factor.
SIDS is a very rare event, but obviously one that causes extreme distress for parents and families. This study suggests another way in which the risk of SIDS may be reduced, and it will undoubtedly prompt more research into the use of fans or other forms of ventilation.
Parents who are concerned about the risk of SIDS could consider using a fan in warm rooms, but this step should be used together with other steps known to reduce risk. These include not smoking in pregnancy or in the home after the birth, placing the infant on their back to sleep, using a pacifier, not allowing bedding to cover the baby’s head, and keeping the room at a comfortable temperature below 21°C.