Bruce Beckwith, MD
What is the Cause of SIDS?
It is common to read in newspapers that the cause for SIDS has been discovered. Some recent examples are elevated T-3, maternal smoking, prematurity, poverty or viral infection. I believe that SIDS is not a disease, but a way of dying. It’s an episode that occurs over a very brief span of moments that results in the death of a baby. Things which preceded that episode may or may not be relevant to SIDS. There are lots of so-called predisposing factors such as prematurity, but being a preemie is not the cause of SIDS. So many of the causes that we read about are really factors which describe a population of SIDS victims, but do not explain the cause of death.
In approaching SIDS, the thing that happened last is most important, namely how did the baby die? In other words, what was the mechanism of death? Perhaps the most significant original observation I have made on SIDS bears on that specific point – how they die. It is my belief, based upon many research findings, that at the end of a breath, as a baby lets out air and is ready to take a new breath during sleep, the airway closes off in the back of the throat. That closure makes it impossible for the baby to take a next breath. As a result, the baby may change position.
The face may come to be straight down into the bedding, or might get wedged in a corner of the crib, or a blanket may be pulled over the head. These conditions may suggest the baby suffocated, but in fact, specific research has been done proving that even tucking the blankets on all four sides of the crib mattress does not cause blood oxygen levels to drop. So even when appearances may suggest the baby might have suffocated in its bedding, these appearances are misleading, and are the result of the way they die, not the cause of death.
If there is evidence of airway obstruction, how can we so confidently rule out suffocation? I emphasized earlier that the obstruction occurred at the end of a breath. One of the findings in the examinations of the SIDS babies are little pinpoint hemorrhages found in the chest organs of 87% of the cases. These hemorrhages result from instantaneous and complete closure of the upper respiratory tract at the end of a breath.
How Can a Healthy Baby Die so Suddenly?
Why would the airway become obstructed during sleep in a healthy and thriving baby? Nobody knows for sure. If one accepts that we understand how they die, the next question is, “Why do they die?” A concept that I have found appealing for many years is that this stoppage, or obstruction of the airway is not due to a disease process or an abnormality of the baby. However, it is a reflection of the fact that babies at this time of life are undergoing an incredibly rapid state of growth and maturation.
Many important changes are occurring at the age when most SIDS occurs. The infant is, among other things, coming into an age where he is beginning to sleep through the night. That is not just a simple change in habit pattern, but a change that is very fundamental and has to do with control mechanisms in the brain. Centers that are beginning to be active in the baby’s brain did not even exist when that infant was born.
Virtually all of brain growth occurs in the first two years of life, and the growth rate in the first six months is the most rapid of any time in life. During the time when these important control centers are in a period of transition, abnormal messages might come down to the organs of respiration, one of which is to “close off’ rather than “open up.” Normally, at the end of a breath, the throat collapses or closes, then opens up prior to a new breath being taken. However, if the wrong message comes down from the brain, the throat may stay closed instead of opening. That wrong message is not necessarily a result of this baby being abnormal, but occurs in a normal baby whose brain is growing at a tremendously rapid pace.
This view of SIDS is certainly one person’s view and is not shared by everybody who works in SIDS. It is a view which I find very reasonable and helpful; the concept is that the baby was normal when it dies, not abnormal. There is no way for anyone to predict that a normal baby is going to have this kind of abnormal event. Many factors may contribute to that event. Minor irritation of the airway may, by increasing the sensory input coming up the nerve from the throat to the brain, increase the likelihood of abnormal messages to come down. Thus, perhaps we have a connection with the minor respiratory infections, which are present in many cases.
How is the SIDS Diagnosis Made?
In doing a postmortem examination, we do not see the lethal mechanism directly. After death, muscles relax, so the pathologists do not find the throat muscles clamped shut. There are little things that we find consistently, such as the pinpoint hemorrhages I mentioned earlier, but none of those things account directly for death. They are only clues to the way they die, and helpful to the pathologist in diagnosing the case as SIDS.
The SIDS victim did not die without diagnosis. The baby died of a very distinctive entity. Any of you who are familiar with sudden infant death will know that the typical case falls into a narrow age range, and seemed to be okay except maybe for a cold, ate his last meal normally, was put to bed and was later found dead.
You know when you hear that story what the pathologist is going to say. However, when the story is different, then you really want to know what the pathologist found. When there are some unusual features to the case, the postmortem becomes especially important, as there are many conditions other than SIDS, which can kill infants and young children suddenly.
If we take all babies under one year, who have 1) died unexpectedly, 2) during sleep, with 3) no history of alarming symptoms, such as seizures, temperature over 105 degrees, and 4) no external findings to allow one to suspect a cause of death (like a fractured skull or a skin rash), 92% of cases will be diagnosed as SIDS after-autopsy.
If the infant is two or three months old, it would be more like a 95% certainty. In some communities it is not possible to get an autopsy, but one can usually do an x-ray examination to add to these four criteria. With the presence of a normal full body x-ray, the chances the death was due to SIDS goes from 92% to 98.2%.
My Baby was not a Typical SIDS Case
Each of you who have personally experienced SIDS probably feels that your baby in some ways does not fit the classical profile. You read about “high risk” babies and it’s very easy to confuse the concept of “high risk” with “typical.” For example, a “high risk” baby might be born weighing less than three pounds to a disadvantaged family in the winter months. The risk to that baby is perhaps one in 50. If your baby was a fullterm, 8-lb. baby who died in the summertime, and was a girl, it does not sound typical of the “high risk” baby that you hear about.
However, in fact, most SIDS babies are not drawn form the “high risk” population. There are many more babies in our society who are in the “low risk” population, and the majority of SIDS babies are from this “low risk” population. Thus, the 8-lb. baby is a more “typical” SIDS victim than is a 3-lb. preemie, even though that preemie had a higher individual risk of dying.
Because there are so many full-term babies, they constitute the majority of SIDS babies. The same principal applies to the other so-called “high risk” factors. Therefore, these things you read about “high risk” SIDS babies often lead to confusion and it is important to understand that “high risk” and “typical” are very different concepts.
Any one case is a single dot on the bell-shaped curve, and it could fall anywhere on that curve. The description of a population as a whole does not describe each individual member of that population. That is an idea that is often difficult to get across. I do not know if the totally typical case of SIDS ever has occurred.
Every baby that ever died was an individual, and every person who has lost a baby identifies SIDS with that particular individual – the hair color, behavioral patterns, and the medical history of the baby is the profile of SIDS to that parent and family.
It is important for families to be able to appreciate that because that baby seemed different than the other children in that family, it does not mean that difference was in any way related to the death. My experience has made it very clear that there is no typical pattern of behavior, for example, in babies who later die of SIDS.
My Baby Cried Out the Night He Died and I Feel so Guilty Because I Did Not Respond
This was a death caused by airway obstruction and babies cannot cry when their airway is obstructed. Therefore, when that baby was crying, he could not have been dying. He cried, went to sleep, and then died later. Not responding to that cry had nothing to do with the fact that the baby died. Babies do not die from crying.
Since SIDS Only Occurs During Sleep, If I Had Awakened My Baby Would He Have Died?
My answer has to be “no, he wouldn’t have died then.” However, how in the world could anybody know at what moment it was going to happen? The way to prevent SIDS would be never to let a baby sleep, and that is obviously impossible.
Is SIDS Contagious?
Again, the answer is “no.” My personal experience with over 1,200 cases includes not one example where a SIDS victim was closely in contact with another SIDS victim (except for three cases of twin SIDS cases). There are times in every community when there are more SIDS than other times. When viral diseases of certain kinds are sweeping through the community, the incidents of SIDS will climb. Nevertheless, there is no “crib death virus.”
Will It Happen Again In My Family?
SIDS is not a hereditary disease. There are two widely quoted articles in the research literature that says that it may be familiar to genetics. Each of those came up with a risk figure that scares everybody – of 1 in 50. Each of those two papers contains some important errors, so that the true figure is more like 1 in 125. Even these figures exaggerate the risk to siblings. There are two reasons for this.
One reason is the familial aggregation of risk factors, such as prematurity. For some mothers prematurity tends to occur repeatedly because of a relaxed cervix or other factors that make it difficult for her body to retain a baby in utero for nine months. Since 20% – 30% of any SIDS series will be preemies, any large SIDS series is going to include lots of subsequent preemies. Therefore, we would expect that higher risk figures are not shared by the entire population of subsequent siblings, but only by the subsequent preemies.
The other reason is that there are some hereditary diseases that can kill babies suddenly and unexpectedly: heart disease, brain disease and a variety of biochemical disease that require some special studies to diagnose. If you take a large population of SIDS cases, it is likely to be contaminated by a few rare examples of these diseases. One of the most common that we know about is something that we now call familial infantile apnea, and that is a strongly hereditary disorder.
