Leading Medical Theories

Baby Will

Leading SIDS Medical Theories

Based on what we have read, a medical theory called the Triple Risk Model offers the best understanding for why SIDS occurs.  Notice we said SIDS and not SUID.  There are a number of known factors that cause or contribute to a SUID death, but the Triple Risk Model speaks specifically to SIDS.

The model states there are three things that come together to essentially cause SIDS:

  1. An underlying vulnerability in the infant
  2. A critical development period
  3. The introduction of an exogenous stressor

Below is a summary of the model as we understand it.  Keep in mind we are not medical experts.  After losing our baby Will, learning more about this model helped us.  Our goal is to make it easy for others to understand.  While we believe we understand the medical literature enough to summarize it, we may overly simplify certain concepts.  If we have made any mistakes or omission, please let us know (contact-us@babywill.org).   At the very bottom of this page we link to medical journals and other credible experts for those who would like more official explanations of Triple Risk Model.

Triple Risk Model Summary

Underlying Vulnerability
The Triple Risk model is predicated on the idea that some children have an underlying vulnerability.  We think this is the most important factor in explaining SIDS.  As we understand it, there is a part in the human brain located in the brainstem that regulates how we breathe, how we are aroused from sleep, and how we respond to things that threaten our ability to breathe properly.

This underlying vulnerability is actually more of a developmental delay, meaning that in some infants this part of their brainstem develops slower than normal.  As a result, there is a period of time when this child is vulnerable to certain things that would not be life threatening to a baby whose brainstem develops at a normal rate.  For instance, if a baby is sleeping on their stomach and not getting enough oxygen because their face is pressed too closely to the mattress, a normally developed baby will be aroused from sleep enough to lift and turn their head or even wake up and cry.  A SIDS baby does not respond normally because that part of their brain has not developed yet.

At this point there is no known way to test for which babies have this underlying vulnerability.  Researchers have found chemical differences in the brainstems of SIDS babies after they die, but do not yet know how to test for this when the child is alive.1  As such, there is no way of preventing SIDS.  The best anyone can do at this point is to keep known risk factors away from all babies until they make it through their critical development period.  But even then, even when a family does everything right, SIDS can still happen.   We have read accounts of babies who just quietly passed away even when there was no known risk factor present.

Critical Development Period
In addition to the presence of an underlying vulnerability, the Triple Risk Model calls for the presence of a critical development period.  The data suggests this is most often during the first six months of life, as 90% of all SIDS deaths occur during the first six months.

This is an important fact because it implies that the underlying vulnerability in some infants is only temporary.  Essentially, it can be out grown once the child makes it through the development of that part of their brain.

Introduction of Exogenous Stressor
An exogenous stressor is simply an external factor that somehow interferes with the baby’s normal state.  We observe that medical literature typically lists known risk factors for SIDS as such exogenous stressors.  For instance, these external factors could include, but are not limited to sleeping on stomach, soft bedding, bed sharing, etc.

SIDS vs. Suffocation
Early on when trying to understand the Triple Risk Model we struggled.  We remember asking, if a SIDS baby is exposed to some kind of external factor that causes them to rebreathe carbon dioxide to the point where they die, isn’t it really the external factor that caused the baby to die?  Isn’t the real cause of death something like suffocation?  The answer is no.  It is the underlying developmental delay in the brainstem of some children that does not allow the baby to wake up enough to find fresh air.  A baby without this underlying vulnerability would have survived.

Some children clearly do die from accidental suffocation, and these deaths are obviously tragic.  We will use two extreme scenarios to illustrate the difference between SIDS and suffocation as we understand it.  

Scenario one, the baby was sleeping alone, on their back, in an empty crib with no loose bedding.  After an autopsy, review of family medical history, and thorough death scene investigation no other cause of death is apparent.  This child is likely to have had an underlying vulnerability in the part of the brain that regulates arousal from sleep and breathing.  Then something as yet unknown disrupted the baby’s normal state to the point where the baby did not respond normally and the child quietly passed away.  

Scenario two, the baby was sleeping on an adult bed and found pinned between the mattress and the wall.  In this case, there was probably not an underlying vulnerability in the child.  The difference is few if any children could have survived this second scenario.

These are two extreme examples for the sake of trying to draw a clear distinction.  The reality is SIDS deaths are quite often more difficult for investigators to discern.  Take for instance a baby who was found sleeping alone, on their back, in a crib but with a small lightweight blanket covering their face.  Note that this is different than Scenario One above because in this case, in the baby’s crib is a small lightweight blanket.  Thus the crib was not empty.  It might seem inconceivable that a simple small blanket inside the crib caused the baby to rebreathe enough carbon dioxide to cause death.  But this blanket would constitute loose bedding, a known risk factor for SIDS.  For a child whose arousal response system has not yet developed (i.e. an underlying vulnerability during a critical development period) this little blanket could have been enough of an Exogenous Stressor to be fatal.  According to the Triple Risk Model, a child who did not have an underlying vulnerability would have awoken enough to knock the blanket aside so they could get fresh air.

The Triple Risk model says that when a baby has an underlying vulnerability, at a time when the part of the brain that regulates breathing and arousal is still developing, and they are introduced to certain external factors while sleeping, these babies do not respond normally and can die.

More Official Explanations of Triple Risk Model
Do a Google search for Triple Risk Model and it will return over 2.8 million results.  However, here are the three sources we found give the best most credible explanations.

Boston Children’s Hospital
Boston Children’s offers one of the shorter and easier to understand explanations.  This is not surprising given this is the Hospital of Dr. Hannah Kinney who is a leading SIDS researcher.  Here is a link to a page which talks specifically about the Triple Risk model.  And here is a link that talks briefly about Dr. Kinney.

2011 AAP Recommendations
The American Academy of Pediatrics (AAP) recent recommendations on SIDS includes a good summary of the Triple Risk Model as well as SIDS in general.  It is definitely written for an audience with a medical background, but it offers some of the best information.  Here is a link to the 2011 AAP Recommendations, look specifically to page 7 for the part about the Triple Risk Model.

New England Journal of Medicine (NEJM)
A medical progress article entitled The Sudden Infant Death Syndrome written by Dr. Hannah Kinney and Dr. Bradley Thach was published in the New England Journal of Medicine in August of 2009.  Though it is now slightly dated, the article remains in our opinion one of the best summaries on SIDS.  Among other things, there is a whole section on the Triple Risk Model.  The article is written for a medical audience, but even without having a medical background we were able to follow it (albeit, sometimes with the help of a dictionary).



1 Source:  http://www.childrenshospital.org/az/Site1654/mainpageS1654P5.html