Crib Mattresses and SIDS; cases continue to be reported of infants placed supine (on back) and found prone (on tummy) on firm crib mattresses with evidence of suffocation/positional asphyxiation (rebreathing) and others becoming entangled and suffocating in sheets.
In fact, here are over 3,500 sleep-related deaths among U.S. babies each year, including sudden infant death syndrome (SIDS), accidental suffocation, and deaths from unknown causes according the CDC.
Crib Mattresses and SIDS – The Science
“The first few times babies who usually sleep on their backs or sides shift to the prone (lying face down) position, they have a 19-fold increased risk of sudden death,” says senior author Bradley T. Thach, M.D., a Washington University pediatrician at St. Louis Children’s Hospital. “We wondered if these babies, finding themselves face down, fail to turn their heads to breathe easier. If so, is that because their reflexes haven’t developed far enough or because they just don’t wake up?” The findings also indicate that good head-lifting ability while lying prone may not be sufficient to protect a baby from SIDS. “Many parents think that if a baby can lift its head, he or she is okay to sleep prone, but that is a false assurance,” Thach says (Paluszynska 2004)
Thach and his colleagues studied 38 healthy infants aged 3 to 37 weeks. Half of the babies usually slept prone or had a history of turning prone during sleep. The other babies had never slept prone. The study is reported in the December 2004 issue of the journal Pediatrics.
The researchers constructed a moderately asphyxiating surface, a comforter placed over a foam rubber mattress with a two-inch deep circular depression that would lie directly beneath the baby’s face. When babies sleep face down on the surface, they “rebreath” air they have exhaled, and this air can have high amounts of carbon dioxide. A catheter taped beneath the babies’ noses allowed monitoring of carbon dioxide levels.
After four to five minutes of sleeping face down on this surface all 38 babies awoke and attempted to get fresher air. The babies with experience sleeping prone generally lifted and turned their heads to either side when they sensed the air was stale, thereby increasing their supply of oxygen-rich air. In contrast, the inexperienced infants generally nuzzled the bedding or briefly lifted their heads and then resumed sleeping face down. Overall, babies inexperienced with sleeping prone spent more time fully face down than their more experienced counterparts.
Nuzzling produced only a transient lowering of carbon dioxide levels at the nose, while complete head turns produced larger, sustained decreases in carbon dioxide. Head lifts also reduced carbon dioxide levels, but the decreases lasted only as long as the baby’s head was raised.
The researchers suggest that babies learn through experience which head movements decrease the discomfort associated with breathing high carbon dioxide levels. Therefore, babies with experience sleeping prone are better able to avoid conditions that may trigger SIDS. The research results support the hypothesis, advanced by others, that SIDS may result from insufficiently learned airway protective responses.
The findings also indicate that good head-lifting ability while lying prone may not be sufficient to protect a baby from SIDS. “Many parents think that if a baby can lift its head, he or she is okay to sleep prone, but that is a false assurance,” Thach says. “Parents and other caregivers should never place an infant in the prone position until he or she shows the ability to spontaneously turn all the way over. Back-sleeping should continue to be strongly encouraged to protect against SIDS.”
Crib Mattress and SIDS – The Prone Position
Research on infants who are novice at prone sleep has demonstrated they are less likely to respond effectively to CO2 accumulation making them especially vulnerable (Paluszynska 2004). Researchers out of New Zealand have shown that over one quarter of the infants who died of SIDS in the prone position in their study were last placed non-prone (on their back). These researchers suggested that an infant’s competence in escaping from potentially lethal situations during prone sleep may be impaired by inexperience in prone sleeping (Thatch1999). Their findings were later supported by Dr. Moon and colleagues in their review of infant sleep related deaths in child care settings (Moon 2000). Unfortunately this infant inexperience in prone sleep is now a common unintended consequence of the successful back to sleep campaign.
Babies who never sleep on their stomachs don’t learn behaviors that may lessen their risk of SIDS, researchers at Washington University School of Medicine in St. Louis have found. Even so, the researchers caution that infants should always be placed on their backs to sleep.
Crib Mattresses and SiDS – The Introduction of Air Permeable/Breathable Crib Mattresses
Air permeable/breathe-through crib mattresses are the best defense for a baby that rolls in the middle of the night and ends up sleeping face down. This is the most successful approach to preventing the tragedies we see relating to crib mattresses and SIDS. A breathe-through crib mattress is designed to prevent the accidental suffocation/positional asphyxiation (rebreathing) when baby rolls in the middle of the night.
Crib Mattresses and SIDS – Published Relevant Scientific Case Controlled Studies Supporting the Recommended Use of Air Permeable Crib Mattresses:
Dr. James Kemp and colleagues were some of the first to study the potential for various sleep surfaces to prevent infant rebreathing. They found that the firm crib mattress and four of the five surfaces designed to prevent rebreathing consistently allowed lethal rebreathing of CO2. Only one product—an air permeable crib mattress—was able to maintain CO2 levels below this threshold. The authors go on to say that “even firm crib mattresses could pose a rebreathing threat when vulnerable infants sleep prone.”
Crib Mattress and SIDS – The Novice Tummy Sleeper
Studies show that unaccustomed prone sleepers, including infants who are placed supine and roll prone have an increased risk of SIDS (O’Hoir 1998 and Mitchell EA 1999). These studies and others have shown that nearly half of SIDS victims unaccustomed to prone sleep, were discovered in the face-straight-down position. Many of these infants were found on a firm crib mattress. Dr. Kemp’s data supports that if vulnerable infants were placed on an air permeable surface, they would experience less risk of rebreathing should they inadvertently roll prone.
Crib Mattress and SIDS – Breathe-Through Crib Mattress Testing
In 2011, Dr Ephraim Bar-Yishay and colleagues provided the second study on CO2 accumulation and rebreathing on six infant sleep surfaces—an air permeable crib mattress, two conventional firm crib mattresses and three mattresses with an additional layer or topper designed to improve air flow (Bar-Yishay 2011). The breathe-through crib mattress had a significantly faster rate of CO2 elimination and only the air permeable mattress was able to prevent CO2 accumulation with maximal CO2 levels significantly lower than that of the other mattresses. They concluded that the breathe-through crib mattress exhibited significantly better aeration properties compared to the other five mattresses including the firm mattresses with tight sheet.
A representative of SafeSleep®, a U.S. manufacturer of a breathe-through crib mattress, contacted the CPSC for recommendations on an accredited independent lab to conduct similar tests on aeration properties on their product. Intertek was recommended because they use a similar mechanical model and methods as designed by Dr. Kemp. The lab compared CO2 elimination on four different surfaces—our air permeable crib mattress, a firm mattress with tight fitting sheet, sheepskin, and a bean bag chair. The latter two are known high risk hazards for rebreathing (Kemp 1991, Kemp 1993) and have been implicated in a significant number of SIDS fatalities. Just as in the studies by Kemp and Bar-Yishay, showed significantly less CO2 retention than the firm crib mattress and the high hazard comparators. Intertek concluded that the the breathe-through crib mattress represents a significantly lower risk hazard for rebreathing than the firm crib mattress. Intertek also compared the air permeability of the breathe-through crib mattress to a firm crib mattress using the ASTM-D737-04 standard test method of air permeability of textiles. Based on the test data, the air permeable crib mattress has an air permeability rate over 330 times greater than the firm crib mattress with tight sheet.
These two well-designed, well-conducted case controlled studies along with the independent CPSC testing lab results strongly support a recommendation for the use of air permeable/breathe-through crib mattresses.
Crib Mattress and SIDS – CO2 Retention and Risk of Rebreathing
The studies outlined above clearly demonstrated that the risk of rebreathing of exhaled air (CO2) is lowest on air permeable surfaces (Kemp 2000, Bar-Yishay 2011). And data from Intertek, a CPSC accredited and recommended lab, shows significantly low risk hazard of rebreathing of an air permeable mattress (lower than the firm mattress with tight fitting sheet). These data demonstrate that the breathe-through crib mattress has significantly lower CO2 retention. All three reports use similar test methods and have similar results.
Crib Mattress and SIDS – Direct Prevention of SIDS and CO2 Hypothesis by AAP
While the studies do not demonstrate a direct prevention of SIDS or suffocation, they rely on the hypothesis of rebreathing of CO2 as a potential contributor for these unexpected infant deaths. A basic pathophysiological principle is the hypothesis that rebreathing C02 is associated with ALTE/SIDS/asphyxia. Indeed no studies have substantiated this hypothesis; however, this is the same hypothesis used by the AAP Task Force to support the majority of their recommendations including the following with quotes taken from the AAP Task Force report (AAP 2011):
1. Supine sleep position: “The prone or side sleep position can increase the risk of rebreathing expired gases, resulting in hypercapnia and hypoxia.”
2. Room-Sharing Without Bed-Sharing Is Recommended: “Bed-sharing might increase the risk of overheating, rebreathing or airway obstruction, head covering, and exposure to tobacco smoke, which are all risk factors for SIDS.”
3. It Is Prudent to Provide Separate Sleep Areas and Avoid Cobedding for Twins and Higher-Order Multiples in the Hospital and at Home: “Furthermore, there is increased potential for overheating and rebreathing while cobedding, and size discordance might increase the risk of accidental suffocation.”
4. Pillows, Quilts, Comforters, Sheepskins, and Other Soft Surfaces Are Hazardous When Placed Under the Infant or Loose in the Sleep Environment: “However, such soft bedding can increase the potential of suffocation and rebreathing.”
5. Avoid Overheating and Head Covering in Infants: “It is not known whether the risk associated with head covering is attributable to overheating, hypoxia, or rebreathing.”
Crib Mattress and SIDS – AAP Recommends Air Permeable Sides in Bassinets and Play Yards
Further, the Task Force recommends air permeable sides when bassinets are used. This recommendation is based on a retrospective review and analysis of infant deaths occurring in bassinets between June 1990 and November 2004 that were reported to the CPSC (Pike/Moon 2008). The authors identified at least six infants who were found with their “face wedged against the side of the bassinet.” While there is no mention of any bassinets having air permeable sides in the study, the study authors (including R Moon who is on the AAP Task Force) recommends “a bassinet with vertical sides of air-permeable material, such as mesh, may be preferable to one with air-impermeable sides.” The Task Force makes the recommendation for air permeable sides based on infants with face wedged against side of sleep environment. Logic would dictate that air permeable/breathe-through crib mattresses as being preferable to air impermeable mattresses to address infants face-straight-down on firm crib mattresses.
Crib Mattress and SIDS – Suffocation/Entanglement in Bedding and Crib Sheets
The AAP Task Force concurs with the CPSC that all loose bedding should be removed from the infant’s sleep environment. The CPSC and the AAP issued an alert in 2001 warning parents and pediatricians of the “hidden hazard in babies’ cribs” of loose sheets based on death reports of infants who suffocated or strangled when they became entangled in their crib sheet. Two of the deaths involved fitted sheets (CPSC 2001). The CPSC now requires that all crib sheets carry a warning that the sheet should not be used if it doesn’t fit properly. CPSC pushed the sheet-making industry to improve the fit of crib sheets on mattresses. However deaths from sheet entanglement remain a risk for infants. In the CDC’s multistate SUID Case Registry, the mechanism most frequently reported for possible and explained suffocation deaths was soft bedding which the registry defines as soft or loose bedding (Shapiro-Mendoza 2014). The loose bedding is not further defined but could be a blanket or fitted sheet that became loose.
Crib mattress manufacturers are not sheet manufacturers. The CPSC defines the industry requirements for mattress size based on ASTM standards. Their length and width requirements are consistent but their requirement for height is “less than six inches” making mattress sizes inconsistent. Because there are no crib sheets made for a given mattress, the crib sheet remains a hazard. The design of the air permeable crib mattress eliminates this risk because no sheet or other bedding is used.
The same data used by the AAP Task Force in its recommendation against the use of soft or loose bedding, also supports a recommendation against the use of a crib mattress sheet when possible.
Crib Mattress and SIDS – Role of Bacteria in Crib Mattresses
A recent review article attempts to establish bacterial infection as having a major role in the pathophysiology of SIDS (Goldwater 2013). The authors debunk the respiratory physiology model both as being unproven and inconsistent with the most plausible physiological events that take place during a SIDS death.
A recent study showed SIDS victims, especially those found prone, are more often colonized with Staphylococcus aureus than living control subjects (Highet 2014). Studies have demonstrated colonization of traditional fiber-filled crib mattresses with Staph aureus (Jenkins 2007) suggesting a source for acquiring these bacteria. While no studies are available measuring colonization of air permeable crib mattresses, the surface is designed to be removed and laundered. The U.S. made model recommends regular cleaning of the surface in a conventional washer and dryer.
Based on the bacterial infection hypothesis, it stands to reason that breathe-through crib mattresses that allow for regular washing of infant sleeping surfaces and removal of fiber-fill from the mattress reducing exposure to these pathogens should be recommended.
Crib Mattress and SIDS – Summary
In summary, scientific data supports the recommendation for use of air permeable/breathe-through crib mattresses to reduce the risk of unexpected suffocation/entanglement and other hazards that may be associated with SIDS/SUID.
Learn more about SIDS and Crib Mattresses here.
Paluszynska DA, Harris KA, Thach BT. Influence of sleep position experience on ability of prone sleeping infants to escape from asphyxiating microenvironments by changing head position. Pediatrics, Dec. 1, 2004.
Patrick L. Carolan, MD; William B. Wheeler, MD; James D. Ross, RRT, RCP; and James S. Kemp, MD, (2000), Potential to Prevent Carbon Dioxide Rebreathing of Commercial Products Marketed to Reduce Sudden Infant Death Syndrome Risk, Pediatrics, 105:4 774-779
Edwin A. Mitchell, BSc, MBBS, DCh, FRACP, FRCPCH, DSc; Bradley T. Thach, MD; John M. D. Thompson, PhD; Sheila Williams, BSc; for the New Zealand Cot Death Study, Changing Infants’ Sleep Position Increases Risk of Sudden Infant Death Syndrome. Arch Pediatr Adolesc Med. 1999;153:1136-1141
American Academy of Pediatrics Task Force on Infant Positioning and SIDS. SIDS and Other Sleep-Related Infant Deaths: Expansion of Recommendations for a Safe Infant Sleeping Environment, Pediatrics; originally published online October 17, 2011; TASK FORCE ON SUDDEN INFANT DEATH SYNDROME DOI: 10.1542/peds.2011-2284
Carrie K. Shapiro-Mendoza, PhD, MPHa, Lena Camperlengo, DrPHa, Rebecca Ludvigsen, MPHb, Carri Cottengim, MAc, Robert N. Anderson, PhDd, Thomas Andrew, MDe, Theresa Covington, MPHf, Fern R. Hauck, MD, MSg, James Kemp, MDh, and Marian MacDorman, PhDd. Classification System for the Sudden Unexpected Infant Death Case Registry and its Application. J Pediatr. Jun 2014; DOI: 10.1542/peds.2014-0180
Paul N. Goldwater1,2 and Karl A. Bettelheim. SIDS Risk Factors: Time for New Interpretations. The Role of Bacteria. Pediatrics Research International Journal. Aug 2013; Vol. 2013, Article ID 867520; DOI: 10.5171/2013.867520
Amanda R. Highet, Anne M. Berry, Karl A. Bettelheim, Paul N. Goldwater. Gut microbiome in sudden infant death syndrome (SIDS) differs from that in healthy comparison babies and offers an explanation for the risk factor of prone position. International Journal of Medical Microbiology. Jul 2014; Volume 304, Issues 5–6, July 2014, Pages 735–741; DOI: 10.1016/j.ijmm.2014.05.007