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How can I know that my baby did not suffocate?

This painful question is asked occasionally by parents and relatives surviving the tragedy of Sudden Infant Death Syndrome (SIDS). The answer is complex and often relies upon circumstantial evidence.


Suffocation causes death as a result of insufficient oxygen reaching the blood. Consequently the cells of the body are unable to function properly and the vital organs fail. Suffocation is generally divided into the following categories: smothering, choking, mechanical and environmental. Smothering is defined as mechanical obstruction of the nose and mouth whereas choking is characterized by an obstruction within the airways. External pressure on the body preventing chest movement and, therefore, respiration, leads to mechanical suffocation. Environmental suffocation occurs when oxygen is displaced from the atmosphere being breathed by the individual.

Many factors argue persuasively that SIDS is not a result of suffocation. The epidemiological profile of SIDS makes it impossible to believe that accidental (or homicidal) suffocation is the mechanism of death in the overwhelming majority of these babies. Infants who die of SIDS generally are between two and five months of age, die more commonly in winter than other months, and are healthy, fed, placed in bed, and then found dead during a period when sleeping was thought to be occurring. When the death scene is investigated, evidence suggesting suffocation is not seen. For example, circumstances which might cause suffocation, such as items in the crib or finding baby's nose and mouth compressed against another surface when discovered lifeless, are not identified. Further, postmortem examination of babies dying of SIDS does not reveal physical signs of occlusion of the nose and mouth, and foreign bodies are not identified in the upper airway. Finally, experienced forensic pathologists are able to discern quite easily the signs of resuscitation as opposed to suffocation.

The epidemiology of a population of babies proven to have died of suffocation stands in striking contrast to the highly repetitious profile of SIDS babies. Among suffocated babies, the age range is wider, occurrence of winter predominance and consistent relationship to sleep are lacking, and a history or recurrent, life threatening apnea is often obtained. Also, circumstances at the death scene and postmortem findings will often suggest suffocation. Another related question is "did my baby die from 'positional asphyxia?'" This diagnosis is sometimes used when the baby is found lifeless in a position which precluded breathing movements of the chest, or the baby was in a position that resulted in its nose and mouth being obstructed. Unfortunately, this diagnosis has been used by some pathologists when the baby was found in the prone sleep position, yet has other findings characteristic of SIDS. The Pathology Working Group discussed this issue at length at the Third SIDS International Research and Global Strategy Workshop Meeting in Scavenger, Norway in August, 1994. They concluded that the exact mechanism of death in SIDS infants found in the prone sleeping position (on their stomachs) remains unknown, and the postmortem findings are not significantly different than those found in SIDS cases found in the supine position (on their back). Therefore, the Pathology Working Group issued the following statement: "In the absence of evidence to the contrary these deaths should be certified as SIDS. Diagnoses such as 'positional asphyxia' are speculative and should not be used in this context."

Article by: Henry F. Krous, M.D., Director of Pathology, Children's Hospital-San Diego Adjunct Professor of Pathology and Pediatrics UCSD School of Medicine, and Vice Chairperson of the California SIDS Advisory Council.

Reprinted with permission from Horizons,
Vol. 1, No. 3, Fall/Winter 1994, California SIDS Program

2/9/97

Dear Doctors:

It is so very hard to write this, because these questions come from the deepest part of my conscious, and the answers might really, really hurt, but I have to know...

My baby died on her stomach and I found her face down. Shortly afterward I read about the "rebreathing theory" or "carbon dioxide poisoning" theory. They are one and the same, correct? This theory haunts me since my baby was indeed face down. At first I was convinced that she had suffocated but the coroner told me that would have been detected in an autopsy. Is this true? So then I became convinced that she had rebreathed her own exhaled air, and therefore didn't realize she was in trouble (because she was in actuality still breathing), hence she didn't know she was in a "bind" and so she didn't attempt to get herself out of that "bind". You see, my baby was only two months and six days old but she could move her head quite well from side to side and could lift her head up and rest on her forearms. I have her on video doing this. Am I pretty much correct on how this theory goes? If so, I have more questions.

Can this carbon dioxide poisoning be detected in an autopsy? My pediatrician said no, but since he also admitted that he was not a SIDS expert and certainly not an expert on autopsies as he worked with live babies, I would like a second opinion on this.

Another question on this theory. How much of an indention would have to be made for this to theoretically occur? I ask because my baby did have a slight indention in her bedding, not soft bedding, but she was not in her crib so not on her crib mattress. She had a slight indention no deeper than a half an inch to an inch. This haunts me. I have been told that it would have to have been an indention of 2 to 4 inches for enough of a pocket to form and "trap" this rebreathed air. I have been told that the slight indention very well could have been made by the investigating officer. That one's probably just reaching by well meaning family members trying to ease my guilt.

I guess what I want is a pretty clear (in layman's terms) explanation of this "rebreathing theory" and whether or not it could be determined as a cause of death after a thorough autopsy by a reputable pathologist (I am sure that I did have a very qualified pathologist).

Your questions are very good ones. "Suffocation" is a term used in many different ways and sometimes meant to imply struggling but unable to breath. In a general sense, the word should just mean: unable to get in enough oxygen and to get out enough of the carbon dioxide. Used in this way, we do think that low oxygen/high carbon dioxide levels in the body are an important part of the risk that is being associated with sleeping on the stomach on a soft surface or sleeping in any position with thick layers of blankets/quilts/comforter that could limit access to fresh air. It appears that the babies who do not tolerate such conditions may be less able to "recognize" that the oxygen/carbon dioxide levels are getting worse and to then arouse in some way to correct the problem or to tell you that there is a problem. This is a very important part of SIDS research today.

I know it is easy to say, but please do not feel guilty about information you could not have known at that time, and that we did not understand well enough to tell you about. It is hard to say how soft is "soft enough" so the preferred strategy now is avoid the stomach or side position for sleeping. The kind of "suffocation" that I am referring to is impossible to recognize at autopsy, thus leading to the appropriate conclusion of SIDS.

I hope these comments are helpful.

Dr. Carl Hunt
Washington, DC/Toledo

2/10/97

Would most babies recognize the condition of low oxygen (rebreathing) and then struggle or cry?

Yes, most babies automatically sense (as most of us adults also do) when the oxygen level is too low and/or the carbon dioxide level is too high (this is why those of us used to sea level do not sleep as well when at high altitude). The normal response is to arouse from sleep at least long enough to correct whatever was causing the problem. An important hypothesis to explain at least some SIDS is that the ability to sense an abnormal oxygen/carbon dioxide level and to arouse from sleep is impaired. Problems associated with prone sleep position and/or soft bedding may at least in part be related to this arousal problem.

I hope this answers your questions.

Dr. Carl Hunt
Washington, DC/Toledo

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