Update on sudden infant death syndrome

Update on sudden infant death syndrome – includes related articles

Sudden infant death syndrome or SIDS shatters parents and bewilders doctors. It’s the leading cause of death in Canadian babies aged two weeks to one year, affecting one to two per 1,000 infants. The ultimate mechanism of death by SIDS in seemingly healthy babies is cardiac (heart) or respiratory failure of unknown cause. The typical pattern of SIDS is that babies are found lifeless for no discernible reason. A century ago, such “crib deaths” were attributed mainly to carelessness or drunken mothers who rolled onto their children and smothered them while asleep. Later, when separate beds for babies became popular but brought no reduction in crib deaths, these infants were believed to have suffocated in their bedding or choked on their vomit. Only in the 1940s did investigators stop accusing parents of misconduct and begin to explore other reasons for these mysterious deaths. Many theories have been proposed to explain SIDS, only to be discarded later as false leads. There may in fact be several contributing factors. Recent evidence suggests that, despite the outward appearance of good health before death, SIDS babies probably have “something wrong”- some as yet unidentified abnormalities – which predispose them to sudden death. Piecing the puzzle together is an ongoing detective story.

What exactly is SIDS?

The definition of SIDS has now been updated to discard the idea of SIDS babies as “perfectly healthy.” In 1989 the National Institute of Child Health and Human Development modified the previous definition of SIDS to read: “the sudden death of an infant under one year of age which remains unexplained after the performance of a complete postmortem investigation, including an autopsy, an examination of the death scene and full review of the case history.” Experts strongly advise a thorough on site investigation of all sudden infant deaths – all too often neglected. Thorough postmortems are crucial to rule out disease, birth defects, environmental causes and criminal abuse as causes of death.

The new definition excludes identifiable reasons for sudden infant death, numbering as SIDS only those where exhaustive investigation tums up no known reason for death. Infant deaths due to food poisoning, allergies (for instance to cow’s milk or dust mites), child neglect or infanticide – formerly blamed for crib deaths – do not qualify as SIDS since there is a known cause of death. Nor are babies who suffocate on bedding or have inborn errors of metabolism (metabolic abnormalities) or any cases not thoroughly investigated classed as SIDS. About 10 per cent of cases suspected of SIDS before autopsy later turn out to stem from other conditions that are easily confused with or mimic SIDS such as fulminant (galloping) meningitis, encephalitis (brain inflammation) and overlooked congenital flaws such as serious heart defects.

Some common features in SIDS deaths

Epidemiological (population) studies reveal a common pattern in SIDS deaths. The majority occur in babies under six months of age, mostly in those between one and four months old. SIDS is more common in males (about 60 per cent of cases) than in females, more frequent in blacks and natives than whites and least common among Orientals. There is also a distinct seasonal link: two thirds of SIDS deaths occur in winter. Some experts link the seasonality of SIDS to possible over-swaddling and over-heating of vulnerable babies in winter time. Poor infant temperature control is believed to be one possible contributor to crib deaths. (When discovered, SIDS babies are often very hot.) Researchers also speculate about the possible triggering role of winter viruses, with nothing definite proven.

The fact that SIDS babies die during sleep has prompted researchers to focus on sleep patterns and to speculate that SIDS babies have some flaw in respiratory rhythms and the arousal mechanisms that fine-tune breathing control. Although SIDS isn’t yet traceable to any specific disorder, many scientists believe that these babies may have delayed brain maturation which subtly undermines normal breathing, making them prone to SIDS. Recent work at the University of Toronto’s Hospital for Sick Children indicates that SIDS babies may be born with borderline abnormalities in pans of the brain that regulate breathing. The studies suggest that bouts of hypoxia (oxygen shortage) before or soon after birth may delay maturation of those parts of the nervous system (brain stem) which control breathing, disrupting respiratory rhythms during the early postbirth months. Although not readily detectable, the maturational lag could make these infants extra-susceptible to respiratory problems during sleep. Very likely, infants who die of SIDS have one or more vulnerabilities that arise in fetal life so that a minor stress or trigger, insufficient to cause death in a normal infant, may tip the balance.

The only consistent, visible abnormalities found in SIDS babies at autopsy are tiny petechial or pin-point hemorrhages (bleeding spots) on the surfaces of the thymus gland, lungs and heart. These hemorrhages may be a “terminal event” that occurs at the time of death due to increased pressure across blood vessel walls. More detailed neural (nerve) examination shows that some SIDS babies have signs of damage in areas that control breathing – traces of astrogliosis (scarring) in the brain stem; retarded myelination (fatty nerve sheathing) of the vagus (10th cranial) nerve and immature synapses (nerve connections) in the brain stem. In addition, some SIDS babies have altered neurotransmitter levels (e.g., excess dopamine) which could dampen arousal mechanisms in sleep. Finally, the risk of respiratory collapse in SIDS babies may be increased by a crowded upper . airway, especially a larger than usual tongue – a finding that remains to be confirmed.

Looking for links: who’s most at risk for SIDS?

No available tests can predict which infants will succumb to SIDS. Most babies with known risk factors, such as low birth weight or minor congenital flaws, do not die of SIDS. There’s no known way to prevent SIDS. There is no genetic basis for the disorder nor any specific enough characteristics to spell out the danger. The majority of SIDS infants don’t have any noticeable breathing difficulties or warning signs of impending catastrophe.

However, premature and low birth-weight babies and those with slower than normal growth rates are at above-average risk of SIDS. In one California study, babies weighing 1,500-2,000 grams were far more likely to die of SIDS (6.5 per 1,000 births) than those weighing over 4,500 grams at birth (0.87 per 1,000 births). About 50 per cent of SIDS babies had a mild illness shortly before death, usually an upper respiratory (cold virus) or gastrointestinal infection. Minor congenital defects such as club feet, hernias and small heart defects are also slightly more frequent than average among SIDS babies.

Profiles of the mothers of SIDS infants support the idea that problems during pregnancy may predispose these babies to unexpected death. For example, women who smoke, are anemic, undernourished, prone to bladder infections or are very young (especially teenagers) are at above average risk of having SIDS babies. Such women often receive scanty prenatal health care, which could disturb fetal health. One Florida study showed a SIDS risk of 3.2 per 1,000 for mothers under age 19 compared with 1 per 1,000 for mothers aged 25-29. However, babies of any parents can die of SIDS.

Infant sleeping position one possible factor in SIDS

Very recent evidence, given much media attention, suggests that some crib deaths may be related to sleeping “prone” or face down on the stomach. Several studies, particularly those from Australia (Tasmania) and New Zealand, have linked the prone sleeping position to elevated SIDS risks. Based on the careful evaluation of numerous studies, the American Academy of Pediatrics issued a 1992 recommendation that normal infants be put to bed on their sides or backs rather than on their stomachs (a change from the currently popular North American baby sleeping position). European studies have also linked the prone sleeping position to higher SIDS rates. For example, in Holland during the 1970s – when infant sleeping positions were changed from the back to the stomach on the advice of pediatricians there was a coincident rise in SIDS deaths. But when the advice switched back to a recommendation for placing babies on their sides or backs, Dutch SIDS cases declined dramatically. In Britain, a change in baby sleeping position from prone to supine (on the back) was also associated with a 50 per cent decrease in crib deaths – preliminary findings only.

It’s not clear why sleeping on the stomach might increase crib deaths. Possibly the baby’s face and nose become obstructed and hinder breathing or reduce thermo (heat) regulation. Since heat escaping from the infant’s face is an important cooling mechanism, the baby might become overheated if placed face down. (Around three months of age, a temperature rise is known to destabilize breathing, while lower temperatures produce steadier breathing rhythms.) There are no data suggesting that sleeping on the side or the back harms normal infants. However, sleeping prone is still recommended for certain babies, namely, those who are extremely premature and infants with gastroesophageal reflux (frequent regurgitation).

One University of Toronto expert cautions against placing too much faith in sleeping position as a risk factor until more results come in. The proposed link between sleeping prone and SIDS still begs the question of why its prevalence is so low in the U.S. where so many babies sleep on their stomachs. Some argue that the studies – many done in Australia and New Zealand – didn’t allow for the popular Antipodean habit of putting babies to sleep on sheepskin bedding to keep them warm in the absence of central heating. The high SIDS rate may have gone down when infants slept on their backs because they no longer breathed in bits of sheepskin.

The apnea or breathing lapse link

One condition that’s received much coverage as a possible forerunner of SIDS is apnea, where a child’s breathing momentarily stops and the baby becomes bluish. Tiny infants often temporarily stop breathing for a few seconds, especially after a deep sigh. Breathing stoppage lasting less than 20 seconds is not considered hazardous. But if the lapses last more than 20 seconds they can signal danger. Such Apparent Life-Threatening Episodes (ALTEs) – to give them their scientific name – often happen in the same age range as SIDS, also more commonly in males than females. One third to two thirds of ALTE survivors have another episode of breathing stoppage and one to two per cent of these infants eventually die.

In some instances an ALTE is traced to a seizure disorder, viral infection (cold), airway obstruction, heart disease or choking, but in half the cases no specific cause is found. Parents who notice a breathing lapse may resuscitate the baby, seemingly with no bad after-effects. Very often a small stimulus – a flick of the finger on the feet – will set the baby breathing again. If that doesn’t do the trick, the next step is vigorous stimulation, perhaps a hard pinch. If that doesn’t work, the parent should begin mouth to mouth resuscitation. (Never shake the baby hard, as it could cause a head injury, even death.) The ALTEs usually decrease as infants get older and are generally not medically significant once the child is six months old. Possibly, had the parents not found and revived these ALTEs babies, they might have been counted as SIDS cases. However, no more than five to seven per cent of SIDS cases experience an ALTE before death.

Having subsequent children: is the SIDS risk higher?

Parents often want to have another baby soon after their SIDS loss. But they must judge carefully whether they’re emotionally and physically ready and have reached a point where a new baby can be accepted in his/her own right, not as a replacement for the lost child. Many parents who have suffered a SIDS tragedy are nervous about having another child. But studies suggest that the risk for subsequent offspring is only very slightly or no greater than for the general population. “However,” says one University of Toronto expert, “counselling parents about subsequent babies is crucial. They need accurate information and plenty of support.” Experts usually recommend that the mother should only become pregnant after she’s dealt adequately with the grief and guilt engendered by the loss.

Counselling SIDS families crucial

The sudden, mysterious death of a seemingly healthy infant from SIDS can cause immense grief, self-blame and anxiety. Parents and other caregivers may mull endlessly over the events leading up to the death. Guilt may worsen the usual anger. denial and intense sense of bereavement that follows SIDS even though no known measures could have prevented the infant death. A full examination often helps to alleviate the guilt and medical experts are urged to explain the importance of autopsy. The police investigation of sudden infant deaths – while initially distressing – ultimately serves to lighten the burden. The first step in counselling families after crib death is to reassure them that nobody was to blame for the tragedy – a difficult message to get across. Parents also need reassurance that SIDS wasn’t the doctor’s fault, as many infants of that age will have had a recent medical check-up. Marriages can become strained and siblings understandably distressed after a SIDS death. The siblings of the SIDS baby must be encouraged to express their grief, self doubts and confusion. Some siblings may not show their grief but “act out” by renewed bed-wetting, naughtiness or poor school work. Expert counselling, support and sharing experiences with others who’ve been through similar situations can be a great help.

Babies seem to be at above average SIDS risk

* In winter time.

* If their mothers smoke cigarettes during and/or after pregnancy.

* If their mothers are drug addicts.

* If their mothers got insufficient health care while pregnant (“poor uterine environment”).

* If parts of the baby’s brain that regulate breathing remain immature (delayed development) – perhaps due to short bouts of oxygen shortage.

* If infants are overheated (faulty body temperature control) over-swaddling or heavy bedding may make the body “work too hard” to keep down body temperature.

* If they’re underweight at birth, slow to gain weight or premature – especially with lung disorders.

* If they’ve had serious apnea (temporary breathing stoppage). Several “blue spells” may signal a flaw in breathing control.

* If bottlefed rather than breastfed.

* Possibly if they sleep on their stomachs – a recent finding still to be confirmed.

Breathing monitors questioned

Home apnea monitors are devices with electrodes attached to the infant that trigger an alarm if the child’s heartbeat becomes too fast or slow, or if the baby stops breathing for more than 20 seconds. Their use has been explored as a way to prevent SIDS in babies at higher than average risk. alerting parents when infant breathing halts. But no studies have so far shown that monitoring prevents SIDS. While five to 10 years ago infants thought to be at risk of SIDS might automatically have been put on a monitor, they’re less popular today. Monitors give frequent false alarms and babies wearing them have died of SIDS. Other criticisms levelled at baby monitors include the lack of regulatory standards, the need for training parents in their use and the 24-hour-a-day vigil. Parents may not dare to weed the garden, take a shower, or watch TV for fear of missing the alarm. When the alarm does go off, parents may rush in only to find the baby breathing normally, not knowing why it sounded. However, for a small subset of infants, especially those known to have suffered serious apnea, home monitors may be of some value. The best monitors have an inbuilt “memory” that can relay what happened before the alarm sounded – whether and how long breathing ceased. and how fast or slow the heart rate was.

Advice to parents about SIDS

* Have good medical care and adequate nutrition during pregnancy.

* Keep baby in smoke-free surroundings (smoking by either parent as well as second-hand smoke are clearly linked to SIDS).

* Put baby to sleep on a firm mattress.

* Breastfeed if possible.

* If “blue spells” are noticed in the infant, get prompt medical advice.

* Try not to let the baby get too hot (don’t over-swaddle).

* Never have the infant’s face covered by bedclothes.

* Avoid thick blankets, pillows or bumpers in the crib.

* Try not to let the infant sleep on its stomach.

* Put the baby to sleep on its side or back (a rolled-up towel along its back will help to keep the baby on its side).

For further information, contact: The Canadian Foundation for the Study of Infant Deaths; Phone: (416) 488-3260

COPYRIGHT 1992 Strategic Inc. Communications Ltd.

COPYRIGHT 2004 Gale Group