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SIDS and Apnea: Difference of Opinion

Date: Tue, 22 Apr 1997

The truth is that how SIDS and apnea are related is
controversial. Part of the problem, I think, centers around the
use of words, as I mentioned in a pervious E-Mail. It is
certainly possible that a baby can die if he/she stops breathing
and does not start again. Since not breathing is defined as
"apnea", it would be true to say that apnea can cause death. It
is likely that this would not show up on autopsy, and thus, in
most places, the cause of death would likely be called "SIDS".

Much of the time that people ask if apnea and SIDS are the same,
they are asking if "apnea babies" are the same as those who die
from SIDS. In this respect, I do think there are some
differences. First, for the vast majority of SIDS victims, the
first sign of a "problem" was finding them dead. For babies who
are found blue, limp, and not breathing, but can be resuscitated
(Apnea babies, or apparent life-threatening events [ALTE]), they
have often had a number of episodes, and yet managed to survive
them all. This seems to be a major difference. Thus, it is
unclear whether apnea babies and SIDS babies are the same. I
believe that most SIDS researchers think they are not identical.

The last issue is how often is apnea (not breathing) the cause of
SIDS. This is not known either. Dorothy Kelly, now from Texas,
has reported from recordings of babies who died from "SIDS" while
on recording home monitors. She finds that the heart may stop or
abruptly slow, even though babies are still breathing. Thus, it
is not certain whether SIDS is primarily a respiratory or cardiac

I hope this helps. On the other hand, if you are more confused,
then you can join the rest of us. It seems like the more we
learn about SIDS, the more confusing the picture becomes. Thanks.

---Tom Keens
Children's Hospital Los Angeles

Date: Sun, 13 Apr 1997

>IT seems there is a clear difference of opinion between scientists in the
>United States and in Britain about SIDS and apnea.

[parts snipped...]
>But the senior consultants and researchers I have approached here in the UK
>all seem to agree that SIDS is self-evidently a form of apnea, and that
>SIDS and apnea do not need to be differentiated. Dr. Richard Wilson,
>Consultant Paediatrician at Kingston Hospital and Vice Chairman of FSID's
>Information and Support Committee explained that "this may be a confusion of
>words"; apnea simply describes the fact that SIDS babies stop breathing.
>And Dr. Iona Jeffrey, Consultant in Paediatric Pathology at St. George's in
>London, was clear that "of primary importance, we think, is that the baby
>stops breathing". Her confidence about this is based on the supposition
>that if something had gone wrong in the brain it would show up clearly in a
>postmortem examination (as a swelling or haemmorage, for example) whereas
>infact only tiny changes are observed in the brain of a SIDS victim, and
>these are consistent with the failure of respiratory mechanisms.

The confusion surrounding the "apnea issue" is understandable in view of the widely differing opinions and beliefs about "apnea and SIDS" held by health professionals. However, within the scientific community of researchers who study SIDS, control of cardiovascular and respiratory development, and developmental physiology, there is very little disagreement and a reasonably clear consensus.

To understand the source of the confusion one must understand how "apnea" got to be so closely associated with SIDS in the first place. The term "apnea" simply means "not respiring" in the sense of not moving air into and out of the lungs. There are only 2 ways this can happen: 1) cessation of breathing efforts and 2) blockage of the upper airway, so that no air can be taken in, in spite of continued breathing efforts. The first (#1) is called "central apnea", defined as cessation of respiratory effort (breathing) due to lack of breathing signals (drive) from the brain respiratory control centers. It is called "central" because the apnea is caused by a momentary lack of nerve impulses from the CENTRAL nervous system to the diaphragm. This is the type of apnea that has, in the past, been associated with SIDS. We now know that all normal infants have central apnea; most central apnea reflects normal developmental physiology. The second type of apnea (#2 above) is called obstructive apnea, because the "not breathing" is actually caused by blockage of air entry into the lungs because it cannot pass through the upper airway. In the case of obstructive apnea, the person continues to make breathing efforts, but no oxygen can be taken in because the airway is blocked.

The excessive focus on central apnea started 15-20 years ago when it was reported (by Dr. Steinschneider) that central apnea might be associated with SIDS. This lead to the so-called "apnea hypothesis" of SIDS, in which it was postulated that SIDS infants, for unknown reasons, simply stopped breathing and died. It was assumed that the "central apnea" recorded on overnight recordings of breathing/heart rate was a sign of a breathing disorder that, in some cases, manifested as prolonged fatal apnea. An additional assumption was made, at that time, that if central apnea was correlated with SIDS, then central apnea could be used as a *predictor* of SIDS. Within a relatively short time frame, physicians were performing overnight breathing recordings the a baby's of breathing/heart rate (the "pneumogram"), and using these to "predict" which infants might be at increased risk of SIDS and, therefore, to select those infants that should receive a home monitor. At least in the U.S., the heavy focus on "central apnea" and the use of pneumograms and monitors in this way became standard practice for many many years. However, the foundations of these associations and practices were shaky, and under the weight of new scientific evidence, these assumptions and practices would later collapse and be shown to be invalid.

What continues to amaze me is that this "debate" is still going on in 1997. It has been known for over 10 years that the so-called "pneumogram" has no predictive value for SIDS. This was CLEARLY spelled out in the 1987 NIH Consensus Conference on Infantile Apnea and Home Monitoring. In addition, those involved in the field, back in 1987, were quite clear on the point that the heavy focus on central apnea was erroneous. Dr. Hunt, in a 1987 article on the possible causes of SIDS, went into this history in some detail, explaining how the excessive emphasis on central apnea was erroneous and that scientists should be studying other aspects of cardiorespiratory control and other possible causes of SIDS. So, within the SIDS and cardiorespiratory control research community, this issue has been settled and clear for many many years. Dr. Tomares, who you mentioned in your posting, trained in my laboratory during 1992-1995 and his views on the subject largely reflect what the cardiorespiratory control research community has been saying for a decade.

Getting back to the US-ENGLAND aspect of your posting, what is even more amazing is that the research that provided the crushing blow to the "apnea hypothesis" of SIDS came from British researchers. Dr. David Southall and colleagues from several other countries performed huge studies of many thousands of babies, examining the predictive value of "central apnea". They did this sort of recording, the "pneumogram" on thousands of infants over a period of years. Some of those infants died of SIDS, allowing the researchers to go back and analyze whether the "pneumograms" contained data that would or could have predicted which infants were at increased risk for SIDS. As it turns out, pneumograms (and particularly central apnea) had *no* predictive value in determining which infants were at risk of dying. Other studies were done and, over the last 10 years it has become abundantly clear that central apnea, per se, is NOT a predictor of SIDS risk. There have also been several studies that reported infants dying while attached to home memory monitors. Again, these do not show infants simply "stopping breathing". Those studies indicate that central apnea was a final "terminal" event, as you mentioned, not a primary event.

>The position in England is that SIDS can be prevented. There is not such a
>clear-cut view as in the States that SIDS babies can not be resuscitated.

I am not aware that this is so clear in the US. Dr. Keens and I have both written about the issue of non-resuscibility (which, I believe) is posted on the SIDS Network website.

>Clearing this issue up must be of crucial importance in advising SIDS
>parents whether or not to use apnea monitors for subsequent children. The
>position in the States seems to be that you can't "prevent the
>unpreventable" and that monitors simply offer a "placebo effect" for anxious

This, to my knowledge, is not the case in the US. Monitors are used for any infant believed to be at increased risk of sudden unexpected death in the hope that a fatal event can be avoided.

>But in the UK apnea monitors are given to parents in the genuine
>hope that prevention might be possible and with the knowledge that the
>cessation of breathing is the crucial issue in SIDS.

This is another area that we could discuss much more deeply. Home monitors that record ONLY breathing and heart rate may very well be recording the wrong variables, from the standpoint of trying to avert catastrophe. There is considerable evidence suggesting that by the time a baby stops breathing, the sequence of events leading to SIDS is so far advanced that it's too late. So, in this sense, monitoring for "apnea", if indeed it is the "terminal event", is likely NOT the correct approach. This is why in England there has been such a focus on monitoring OXYGEN levels and why the CHIME study is looking very carefully at oxygen levels and other variables that could be monitored to provide an "earlier" warning.

>Does this clear difference of approach represent a fundamental disagreement
>between researchers in the United States and Britain, or is it simply a
>"confusion of words" as Dr. Wilson suggests? If it's the latter, shouldn't
>the international research community pool their understanding in order to
>form a more coherent message about the relationship between SIDS and apnea?

I don't think there is any fundamental disagreement within the international research community. As far as the "more coherent message" is concerned, the message has been out there, written and re-written about many many times and for over a decade, both in the British and US medical press.

Just one more thing, for the record, on this topic. There *is*, in my experience, a rather large gulf between the opinions/views held by many general pediatricians about SIDS versus those held by the SIDS and developmental physiology research community. For a decade or more, in the minds of nearly all pediatricians around the world, SIDS was equated with apnea. Unfortunately some pediatricians haven't kept up with the field and it is still rather common to find pediatricians and family practitioners giving out information that is outdated and now considered wrong. This leads, unfortunately, to a great deal of confusion. Some of the confusion around this topic may result from this.

Hope this is helpful,

John L. Carroll, MD
The Johns Hopkins Children's Center

April 16, 1997

>Speaking of confusion, Dr. Steischneider's web page still asserts that "Back
>to Sleep" is unproven. Do any of the doctors think his assertion has merit?

Depends on what Dr. Steinschneider's web page means by "unproven". There is no question that many countries around the world have instituted risk-reduction campaigns and seen a subsequent drop in the SIDS rate. In some countries the decline in the SIDS rate of occurrence has exceeded 50%. The "switch" from prone to supine sleeping position is widely believed, based on many studies, to account for much of the recent decline in the SIDS rate. However, the link between SIDS rates declining and the switch to supine sleeping is not *conclusively proven*, nor are the mechanisms understood. Although the cause/causes of SIDS are still unknown, there seems to be no question at this point that risk-reduction interventions in a society do lead to a reduction in the SIDS incidence.

Dr. Steinschneider knows a great deal about SIDS and has made several important contributions to research in the area. Perhaps someone should ask him to explain his position.

I had seen the website of the American SIDS Institute a while ago and had read their 'position' on sleeping position. Now they appear to have more information, including a lengthy explanation of their position.

Most of what it says is just restatement of the obvious. Yes, we need more research studies in the US. Yes, we don't yet KNOW with confidence that sleeping position changes are the cause of recent declines in the SIDS rate. Yes, the NCHS statistics are still open to question. However... we do know that in many many countries around the world, SIDS rates have dropped when back-to-sleep campaigns have been introduced. At the same time, in most of the countries, there has been little headway with reducing smoking. Some of these countries also had problems with specific bedding materials, like sheepskins, or other bedtime practices that likely played a role. In my opinion the total body of world literature on the subject is strongly suggestive that switching from the prone to the supine sleeping position has had a significant impact. Do we know that for certain... absolutely not. Certainly, more research is needed and validation of US statistics is needed before concluding further. In fact, NICHD has been and is proceeding with more research on the topic.

On the other hand, there is no evidence so far in the last 7-8 years of 'back to sleep' campaigns around the world that sleeping supine is harmful for healthy infants. So, AAP and NICHD have chosen to go forward based on the 'likelihood' that sleeping position is important. This is explicit in the NIH and AAP statements. The American SIDS Institute, it seems, prefers to hang back, dig in, and wait for more data. In my opinion, the NICHD/AAP approach is the most reasonable. It seems 1) to do no harm, while 2) opening the possibility of reducing the SIDS rate and saving lives IF supine sleeping is associated with a lower SIDS risk in the US (research from other countries strongly supports that it likely is), and 3) in the mean time additional research IS being conducted.

Hope this is helpful,
John L. Carroll, MD
The Johns Hopkins Children's Center

Date: Fri, 18 Apr 1997 13:13:59 -0700

Let me attempt to respond to the comments about differences between SIDS research in the U.S. and in the U.K.

I personally know a number of prominent SIDS researchers both in the U.S. and in the U.K. I do not believe that there are fundamental differences between the GROUPS of researchers in those countries (or elsewhere). However, each individual researcher, or research group, probably does favor a particular theory or view, and the research of that group will be guided by those beliefs.

In general, the majority of SIDS researchers "believe" that the origins of SIDS lie in dysfunction of the brainstem, which is responsible for the neurologic control of breathing, heart rate, sleep/wakefulness, and physiologic (protective) responses to changes in the environment. Presently, there is more circumstantial evidence to favor that SIDS is somehow related to failure of the respiratory system. Thus, it is reasonable to search the parts of the brain which control breathing, the muscles of breathing (diaphragm), and the lungs for clues. On the other hand, much SIDS research also concentrates on sleep and arousal from sleep. Many investigators study the interaction between how sleep or wakefulness influences breathing, and influences potential "rescue" responses. Finally, there is increasing research into possible cardiac responses, and specifically in how the brain controls or influences heart rate and heart rate responses to changes in the environment. To date, all of these lines of research have resulted in progress in our understanding about infants and what might go wrong to cause SIDS. Obviously, however, until the cause(s) of SIDS is known, we will not be able to say which of the above was the most productive. Other areas of research should also be encouraged.

With respect to the "apnea" debate. Strictly speaking, "apnea" means not breathing. Therefore, many of the researchers investigating the role of the respiratory system in SIDS might say that "apnea" is related to SIDS. That is, SIDS occurs when an infant stops breathing, or can not get breathing started again. Technically speaking, this would be a correct use of the word. In the U.S., however, the term "apnea" is often associated with babies who are found blue, limp, and not breathing, but who are able to be resuscitated. These are often called "apnea babies" or "apnea of infancy". I think that most SIDS researchers, though not all, do not believe that babies who die from SIDS and babies who have apnea are the same. In that sense, it would be correct to say that SIDS and "apnea" are different.

A major goal of SIDS research is to be able to stop this and prevent it from ever occurring again. We are obviously not yet there. Certainly "Back to Sleep" recommendations have reduced the numbers of SIDS deaths in many places. Some investigators may still believe that apnea monitors might also reduce the number of SIDS. All of us who use apnea monitors in infants at high risk for a recurrent apnea episode or at statistically increased risk for SIDS "hope" that a monitor will make a difference for that particular child. However, there is no scientific proof that home monitors either do, or do not, reduce a child's risk of SIDS.

I hope this helps. Thank you.

---Tom Keens
Children's Hospital Los Angeles

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