SIDS and Infant Apnea

11 Jul 1998

There are now published studies, mostly from Dorothy Kelly and her colleagues, where recordings from infants who were on home monitors, but who died, were analyzed. These infants died suddenly and unexpectedly, and the autopsy findings were negative, so the diagnosis of SIDS was used. The recordings generally show an abrupt slowing and stopping of the heart, followed by change in the breathing pattern. These are only two-channel recordings. That is, ECG (heart beat) and breathing pattern (chest wall motion). Thus, we do not know what happened to oxygenation, if there was airway obstruction, etc.

These recordings are very interesting and extremely important. However, there are a few qualifications. These infants were on home monitors for medical reasons, thus they were not entirely normal infants prior to death. The information from two channels is limited, and does not include some other things we would like to know, like oxygenation. The recordings begin only 30-seconds before the "alarm condition". Thus, we do not know if other things happened before the recording started. Therefore, it would not be fair to conclude from these that SIDS is due to the heart stopping as a primary event. However, it certainly supports continued research into possible cardiac mechanisms of infant death.

I hope this helps. Thanks,

Tom Keens

Sudden infant death syndrome (SIDS, cot death) is the sudden, unexpected death of an apparently healthy infant, under one year of age, which remains unexplained after a thorough post-mortem investigation. We do not know the cause of SIDS. Based on our current knowledge, there is nothing which parents or caregivers of these babies did to cause their deaths, and there is nothing they could have done to prevent them. We can not predict which babies will die from SIDS before it occurs. It is very common for SIDS parents and other caregivers (baby sitters, child care providers, etc.) to feel guilty about their baby's death. Since medicine and science can not tell you why your baby died, most parents review the pregnancy and life of the baby before death looking for something the parent/caregiver did to cause the death. However, let me reassure you based on the latest research information, that SIDS parents and caregivers did not cause the deaths of their babies.

Infant apnea is a different situation. Infant apnea is diagnosed in an infant who was found limp, blue, and not breathing, but who was able to be revived. This is the major difference between SIDS and apnea. Apnea babies are successfully resuscitated. It is true that they have a statistically increased risk of subsequently dying from SIDS, however, apnea is not the same as SIDS. It is tempting to believe that if you find a limp, blue baby who is not breathing, and you revive that baby, that you have prevented him from dying of SIDS. However, it does not appear to be that simple. Apnea babies usually have survived several such episodes before they get to medical attention. This is very different from the typical SIDS victim who was found dead as the first sign of any potential problem.

I hope this is helpful. Thank you.

Tom Keens
Children's Hospital Los Angeles

Why are apnea babies monitored if apnea is different from SIDS?

Infants who have an apparent life threatening event (ALTE; baby found blue, limp, not breathing, and required resuscitation) have a high risk for subsequent events, and a statistically increased risk for SIDS. These babies are monitored because we can not find a cause of the apnea, can not stop the apneas, and thus monitor infants as the best available management technique. This, at least, allows parents to reach their infant and intervene if necessary to terminate the apnea. Most of these babies probably would not have died, even if they were not on the monitor, but we can not be sure of that. Therefore, home monitoring is prescribed.

Babies who died from SIDS, by definition, could not be revived. Usually, the first time a SIDS baby has a problem is when he/she is found dead. In contrast, many apnea babies have had a number of episodes, even before they are monitored, which they managed to survive. I think this is a significant difference, and it is why I believe that, in general, SIDS and apnea may have some small overlap, but the majority of SIDS victims are different from the majority of apnea babies.

One THEORY about SIDS is that all babies have respiratory pauses during sleep, which can last up to 15-20 seconds. This appears to be normal. The question arises how babies 'rescue' themselves from these breathing pauses. One hypothesis is that waking up, or arousal from sleep, is an important defense mechanism we all have to protect us from potentially dangerous situations during sleep. The THEORY would suggest that babies have many breathing pauses. However, if they do not arouse in response to one of them, they might not be able to get out of the apnea, and this could cause death.

Personally, our group has done a fair amount of research on arousal in infants, and I BELIEVE that it might be important with respect to SIDS. However, this has not been proven.

I hope this is helpful. Thank you.

Tom Keens
Children's Hospital Los Angeles

To respond to questions about monitoring for apnea in SIDS siblings:

The relationship between SIDS siblings and apnea goes back to Dr. Steinschneider who found irregularities in breathing patterns in some SIDS siblings and he has continued to hypothesize that prolonged apneas are associated with SIDS. In addition we know that statistically SIDS is more common in preterm infants especially the most immature ones. These are the very same infants who have apnea of prematurity. This would seem to strengthen the argument to monitor SIDS siblings with an apnea monitor.

However, as we follow more infants on monitors that have died of SIDS we see that apnea is not always the preceding event. Dr. Carroll has already written about this and has published on it in the medical journals. Additionally, we know that there is no statistical association with apnea of prematurity and SIDS. Therefore, there is growing concern among apnea program professionals that we are monitoring the wrong thing. Infants can normally have pauses in breathing. If an apnea is not accompanied by a decrease in heart rate or drop in blood oxygen of what concern are they??

What we know is important is blood and tissue oxygenation. The programs in Europe are following blood oxygen non-invasively with transcutaneous oximeters. Currently these probes need to be changed every 4 hours. The older ones were associated with skin burns. Many hospitals are re-introducing these pieces of equipment into their ICU's. Perhaps we too (USA) will start to use them at home, probably in addition to apnea monitors.

JDDeCristofaro, MD
University Medical Center
Stony Brook, NY
Infant Apnea Program

February 6, 1997

Thanks for this, but it really doesn't fully answer my question. Since many babies who go on to die of SIDS have had episodes of apnea before their death, isn't it possible or even likely that apnea events that aren't fatal are warnings of iminent (sp?) death and the event that a baby couldn't be revived from is just an apnea event that went too far so to speak?

Perhaps I can shed a bit of light on the subject. Apnea is not necessarily abnormal. In fact, it is usually a normal phenomenon that all babies and indeed all people exhibit.

All normal babies have apnea, which is to say, central apnea. The definition we use is "a cessation of respiratory effort for a duration greater than 2 breathing cycles." Therefore, in a person with a respiratory rate of 30 breaths/minute, each breath lasts 2 seconds. Therefore, by this definition, an apnea in that person would be any cessation of respiratory effort that lasted longer than 4 seconds. Apnea, of course, simply means "not breathing".

Having said that, it is well documented now that all normal babies have lots of apnea. Most of the apneas are less than 10 seconds duration but some are longer. We know that normal infants can have apneas up to 20 seconds -- and very recent data suggests that normal infants may have even longer apnea.

An important aspect of apnea is what happens to the blood oxygen level (oxyhemoglobin saturation) when the baby is not breathing. We also know from studies of normal infants that normal babies have intermittent dips or drops in oxygen level, but these are brief, self-limited, mild, and *not* associated with turning blue.

Another important aspect of apnea is what happens to heart rate during the apnea. Again, a part of normal physiology is for heart rate to slow down during apnea... this is normal physiology. From studies of normals, both full term and preemies, we know also that normal infants have dips or drops in heart rate that are brief, self-limiting, and are not a sign of something wrong. When heart rate drops to low levels (normal varies with age) and stays low for more than a few seconds (bradycardia), this may be a sign of something wrong.

So... where does this leave us? The question is not whether a child has apnea or not, they all do, the question is whether a child has abnormal apnea or, as some call it, pathological apnea. There are several ways of defining this but most experts I think would agree that apnea is potentially pathological or a sign of an abnormality when associated with cyanosis (turning blue), changes in level of consciousness (going limp or unconscious or "out of it"), sustained low heart rate for age, very prolonged, or very frequent. So, all babies have apnea - normally. We become concerned about it being a sign of abnormality when it is associated with turning blue, neurological changes, sustained low heart rates, lasts a long time, or is occurring very frequently... all of which could be signs of various possible abnormalities and need further investigation.

In the old days, pediatricians used to do a test called a "pneumogram" and pronounce kids normal or abnormal based on the results. Problem was that they didn't know very well what was normal and they also didn't really know the true predictive value of any of the measurements. Back then many children were classified as "abnormal" based on criteria that are now considered to be of questionable validity. Several studies have looked at the predictive value of pneumograms, with respect to SIDS, and found them to have no predictive value. So, this practice is no longer recommended.

Instead, today, when a child is suspected of being at increased risk of sudden death, we recommend home monitoring with a memory monitor. This yields MUCH more information that is sometimes of great diagnostic value. Dr. Keens and/or Dr. Hunt may wish to comment on the CHIME monitor, which is more sophisticated than the usual home monitor, but even the conventional memory monitor can be a very useful tool when used properly.

Why when babies have had apnea previous to dying and then died, is apnea not considered to have been the cause?

Not in my opinion. To my knowledge, the presence of apnea in an infant has no predictive value with respect to SIDS.

Now... if a baby has 30 second long apnea or turns blue or goes limp... that's another matter. But the presence of apnea per se is not predictive and is not usually a sign of abnormality. It's really necessary to specify whether one is talking about normal apnea or abnormal apnea.

It is known that adults with apnea have died in their sleep in exactly the same way that babies with apnea do - in fact, it's one of the reasons why we still worry about my son dying in his sleep despite the fact that he is almost 8 years old.

Adults also have central apnea normally. Adults and children also have obstructive sleep apnea, caused by upper airway obstruction during sleep. This condition is associated with labored breathing during sleep, snoring, and repetitive drops in oxygen level, and has been suspected to contribute to or cause sudden death in adults.

I just don't think that this issue has been addressed satisfactorily. From the parents that I've spoken with who have lost babies, some of them (not all) have had babies that have had a certain number of episodes of apnea before dying. It just seems too much of a coincidence to think that there's no connection.

Because all babies have apnea normally, one would expect infants dying of SIDS to have had it too, before they died. Perhaps there is a semantic issue here. Maybe when you say apnea you mean something more than stopping breathing.

As Dr. DeCristofaro or Dr. Hunt said recently, the large NICHD study on SIDS revealed that 93% of parents of SIDS victims had *not* seen their baby "turn blue or stop breathing" before the SIDS death occurred.

I realize that this is a bit confusing. I hope I'm being more helpful than confusing.

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

Since many babies who go on to die of SIDS have had episodes of apnea before their death, isn't it possible or even likely that apnea events that aren't fatal are warnings of iminent (sp?) death and the event that a baby couldn't be revived from is just an apnea event that went too far so to speak? Why when babies have had apnea previous to dying and then died, is apnea not considered to have been the cause? It is known that adults with apnea have died in their sleep in exactly the same way that babies with apnea do - in fact, it's one of the reasons why we still worry about my son dying in his sleep despite the fact that he is almost 8 years old. I just don't think that this issue has been addressed satisfactorily. From the parents that I've spoken with who have lost babies, some of them (not all) have had babies that have had a certain number of episodes of apnea before dying. It just seems too much of a coincidence to think that there's no connection.

Actually, at most about 5% of SIDS infants have had 1 or more prior episodes of prolonged apnea. In these few infants, the apnea may be very significant, but the fact is that it generally is not a problem.

I hope this is helpful.

Dr. Carl Hunt
Washington, DC/Toledo

Date: Tue, 19 May 1998
From: Tom Keens tkeens@chla.usc.edu

In reply to a question about the use of a home apnea-bradycardia monitor to detect apnea:

Infant apnea and SIDS are two different entities, though there may be some relationship. A few studies have asked SIDS parents if their baby ever had a frightening apnea (not breathing) spell prior to death. Only a few percent answered that question "yes". Similarly, only a few percent of babies diagnosed with "apnea of infancy" subsequently die from "SIDS". Home apnea monitors were actually originally designed for use in babies who had serious apnea spells (apparent life-threatening events [ALTE]), but who were revived from them. These babies will have more such episodes, and thus a monitor to alert parents to these episodes, so they have a chance to intervene, makes sense. However, many babies with apnea of infancy had many episodes before coming to medical attention and being placed on a monitor, yet they all survived. This is very different from the baby who dies from SIDS. Generally, the SIDS death is the first sign of any problem with this infant, and these infants do not survive.

When a baby is diagnosed with apnea, he/she is likely to have more events, and a home monitor makes sense. It is not so clear whether these monitors have any role in preventing a baby from dying. However, to answer your question, a home monitor should pick up one type of apnea, "central apneas", where a baby simply stops breathing. They will not detect obstructive apneas, where the baby attempts to breathe against an occluded airway. There is no way to diagnose apnea before it occurs. The monitor will tell you when a central apnea occurs (assuming the baby is attached to the monitor), but it can not predict apnea ahead of time.

I hope this helps. Thank you.
---Tom Keens
Childrens Hospital Los Angeles