SIDS (Sudden Infant Death Syndrome)

Sudden Infant Death Syndrome (SIDS) is a condition in which the infant meets with a fatal outcome unusually and unexpectedly, and this may not be explainable usually through history or the routine post-mortem examination (NICHHD. 2006).  Usually autopsies are conducted in case the individual meets with an unusual death, but such examinations are unable to detect any congenital abnormalities or child abuse.  In SIDS, a factor that plays a role in the development of a fatal outcome in the baby includes suffocation (or asphyxia) which is observed in about 80 to 82 percent of all cases (Carl E. Hunt. 2002).  In the US, about 1.3 to 1.4 out of every 1000 babies dies from SIDS.  It is the third most common culprit of post-natal infant mortality in the US.  Usually SIDS occurs during sleep, and hence the American Association of Pediatricians has suggested taking certain precautions in the manner in which infants are put to sleep (Carl E. Hunt. 2002).  More than 50 % of the infants are put to sleep an improper manner resulting in SIDS.  Infants should be put to sleep in a supine position and not facing side-wards or facing down.  Evidence of SIDS even exists in the Bible.  Infants between the age of one month and one year are mostly affected with the condition (40 to 50 %) (NICHHD. 2006).  In neonatal units of hospitals, about 20 % cases of SIDS occurs (C. E. Hunt. 1999).

Autopsy may or may not be able to determine the cause of death.  A detailed examination of the death scene and an evaluation of the family records and the history help in establishing the diagnosis of SIDS (SIDS Center. 2005).  Recently, as there has been an improvement in the manner in which infants are put to sleep, the prevalence of SIDS has dropped to 0.7 cases per 1000 infants (Carl E. Hunt. 2002).  In the US about 12 to 35 % of all infants are placed in a prone position during sleep, whereas in other countries, it is about 2 % (Carl E. Hunt. 2002).  Most of the cases of SIDS occur in the cold months of the year in the US.  Most cases of SIDS occur in males compared to females (SIDS Center. 2005).  About 2 out of every 1000 live births develop SIDS in the US.  The peak incidence of SIDS is around the age or 2 to 4 months (T. Hansen. 1998, pp. 558 and NICHHD. 2006).  Many researchers feel that obstructive apnea plays a very important role in the development of death in SIDS.  Infants suffering from apnea are at a greater risk of developing SIDS (NICHHD. 2006).  The fatal outcomes arising from acute life-threatening events are greater (4 %) when apnea is present in the infant.  Children suffering from acute life-threatening conditions are at a higher risk of developing SIDS (5 %) (Carl E. Hunt. 2002).  However, it may be very difficult to diagnose apnea in the infant, which could significantly help to reduce events of SIDS.  7 % of the infants who die from SIDS have an acute life-threatening condition (Carl E. Hunt. 2002).  Studies conducted demonstrated that infants who die from SIDS have an abnormal breathing pattern compared to those who do not die from SIDS, during the last 24 hours of their life (T. Hansen. 1998, pp. 558).

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The risk factors that may be associated with SIDS may be of two types, namely, internal or biological and external or environmental.  The internal factors include disorders in brainstem control, genetic risk of developing SIDS, development of certain acute life-threatening events, prematurity, metabolic disturbances, infectious causes and ECG changes.  Some of the disorders of the brainstem control include arousal or gasping deficiency, abnormal respiratory patterns, abnormal vagal tone, heart rate defects, sleep-waking abnormalities, blood pressure defect, etc.  The external factors include maternal risk factors and infant risk factors.  The various maternal risk factors include smoking, drugs abuse, malnutrition, lower socioeconomic status, poor prenatal precautions, infant abuse, short periods between pregnancy and development of hypoxia for the baby in the womb.  The infant-related risk factors include age, sex (occurs more in males), race (common in African-Americans), poor growth, sleep abnormalities, infectious diseases, smoking, temperature extremes, etc (Carl E. Hunt. 2002).

Women who consume cocaine during their pregnancy or following birth may lead to the child having even greater chances of developing SIDS.  The risk may be increased also in case the mother is exposed to methadone and heroine. Studies have demonstrated that the breathing pattern of such babies and the ventitatory function goes out of hand (C. Partidge. 1998).  Kandall et al conducted a long term study to determine the relationship between SIDS and long-term use of opioid narcotics.  Infants who had mothers who consumed opioid (hence exposed to these drugs) had a two to four time greater chances of developing SIDS than others during the perinatal period (Carl E. Hunt. 2002).  The exact mechanism by which the drugs act to cause disaster in the infants is not known.  Some researchers feel that it may be due to the action of the drug on the respiratory of the infant.  Others feel that it may be due to associated factors (H. Taeusch. 1998. pp. 107).  Other maternal risk factors associated with the increased occurrence of SIDS include maternal smoking during pregnancy (Tafler. 1995).  Studies have demonstrated that such infants were at a 3 times greater risk of dying from SIDS compared to other infants (Carl E. Hunt. 2002).  Smoking brought about an alteration in respiration, a drop in the Kinase C levels of the brainstem and the arousal responsiveness to hypoxia (Carl E. Hunt. 2002).  As the extent of smoking increased, so did the risk of dying from SIDS.  It would be interesting to study the manner in which indirect smoking affected the rates of SIDS.  Unconfirmed sources suggest that there may be a slight risk of the infant developing SIDS if the father had smoked.  During the postnatal period, the child could also be at the risk of developing SIDS in relation to smoking.  This could mainly arise as the auto-resuscitation mechanism was altered (Carl E. Hunt. 2002).  The later order children are usually at a higher risk of developing SIDS.  Several birth factors such as premature delivered child, low-birth weight, problems experienced during the pregnancy, etc, may increase the risk of developing SIDS (Carl E. Hunt. 1998).

Autopsy report of the infant who has died from SIDS demonstrates mild pulmonary edema and diffused intra-thoracic petechiae.  Adrenal brown fat and hepatic erythropeoisis also increased in children who have died from SIDS.  Signs of chronic asphyxia may be present in about two-thirds of all cases of SIDS.  In the brain stem, deficits such as focal astrogliosis, presence of persistent dendritic spines, decreased myelination, etc, may be present.  There is increased number of astrocytes in the medulla especially in areas where respiration is controlled.  The Substance P (a substance that helps to transmit nerve signals) levels are raised in the Pons (Carl E. Hunt. 1998).  The arcudate nucleus may undergo hypoplasia (this center plays a major role in the control of respiration).  Arcuate nucleus may demonstrate receptor abnormalities.  There is a decrease binding with the kainate receptors, sertonergic receptors and the muscarinic and cholinergic receptors.  These receptors begin to demonstrate decreased density (muscarinic and Kainate receptors) (Carl E. Hunt. 2002).  The epinephrine and the nor-epinephrine neurons are modified in the SIDS (demonstrated through tyrosine hydroxylase immunoreactivity studies).  The asphyxia that develops may be mild, long-term and preexisting.  Some infants have growth retardation during the prenatal and the post-natal periods.  The levels of corticosteroids may be increased in the blood.  The vitreous humor may contain higher levels of hypoxanthine which imply that the tissue hypoxia develops over a long time before death (Carl E. Hunt. 2002).  Hypoxanthine works by depressing respiration.  Adenosine (a substance associated with hypoxanthine) plays a role in SIDS, and studies suggest that hypoventilation may be brought about by adenosine monophosphate and adenosine accumulation (Carl E. Hunt. 1998).

The gene that expresses for the serotonin transporter may be present in several forms in individuals who have died from SIDS.  Hence, the reuptake activity is greater in children with SIDS risk (Carl E. Hunt. 2002).

Studies performed on the brain stem demonstrate a defect of cardio-respiratory control, including arousal responsiveness.  Several autonomic functions such as sleep-waking patterns, blood pressure, etc are affected.  Abnormalities in respiration patterns, chemoreceptor sensitivity, heart control, respiratory rate, cardio-respiratory interaction, asphyxia and arousal responsiveness are affected.  Several defects in the respiratory patterns such as prolonged period of apnea, short but excessive number of periods of apnea, periodical patterns of breathing, a drop in the respiration rate, etc, may be present.  The respiratory center does not respond normally to hypercapnia and situations in which hypoxia exists.  However, some of the normal children may also have similar chemoreceptor abnormalities.  In sleep-linked asphyxia situations, the child does not respond normally as the arousal responsiveness is usually absent.  The auto-resuscitation mechanism (known as ‘gasping’) is usually deficient in high-risk infants (Carl E. Hunt. 1998).

Studies conducted demonstrated that certain genes may be involved with the development of the brainstem during the prenatal period that could lead to control over respiration especially arousal responsiveness (Carl E. Hunt. 2002).  In animals certain growth factors and receptors were required to develop normal breathing patterns (Carl E. Hunt. 2002).  If the experiment animals did not have these factors, respiration was depressed.  Several environmental factors may react with other factors including biological resulting in greater chances of SIDS.  Infants who are put to sleep face down are at a higher risk of developing SIDS, as they can develop obstruction of the airways and asphyxia.  The child is also at the risk of developing a higher body temperature that could increase the risk of SIDS.  Studies have demonstrated that infants having previous sibling who had died from SIDS face the higher risk of dying from the condition.  Birth weight plays a very important role in the development of SIDS.  Children born prematurely and having a lower birth weight are at a higher risk of developing SIDS (Carl E. Hunt. 2002).  Studies even suggest that breastfeeding may slightly lower the risk of developing SIDS (Kids Health. 2007)

Infants who have died from SIDS have demonstrated higher body temperature.  The chances of SIDS are usually higher in situations where the environmental temperature is higher.  Some children with acute life-threatening events may develop abnormal sleep-related sweating (Carl E. Hunt. 1998).

Studies conducted on children who have died from SIDS, have demonstrated that a rise in the heart rate did not bring in a relative reduction of the QT interval obtained during an ECG.  The child may be at a risk of developing ventricular arrhythmia.  Infants who have a larger QT interval during the neonatal period are at a higher risk of developing SIDS.  During sleep and waking states, infants who were prone of SIDS had a higher heart rate compared to normal infants.  During wakefulness states, the heart rate was found to be similar to that of the sleeping stage in SIDS risky infants.  The relation between respiration and heart rate is also abnormal, and such a defect is usually brought about by a drop in the vagal tone.  Vagus nerve disease, injury to the brainstem, etc, play an important role in the development of a decreased vagal tone.  The heart rate is mainly decreased during wakefulness period and hence, the child is at a risk of developing reduced ability to move around.  Such a symptom is usually reported in children who have died from SIDS (Carl E. Hunt. 1998).

Frequently, in the US, infants belong to lower socioeconomic groups may be at a higher risk of developing SIDS.  The condition tends to occur in certain ethnic group.  The incidence is high in African-American, Alaskan and Native Americans and lower in Asians and Hispanics.  The exact cause for this may not be known, but the manner in which these communities put their infants to sleep may be a factor (Carl E. Hunt. 2002).  It is a misconception that infants put to sleep on their backs are at a higher risk of developing digestive problems and would vomit.  However, children with certain medical problems such as respiratory and digestive problems are at a higher risk of developing SIDS (Kids health. 2007).  Earlier, SIDS was prevalent in the colder months.  However, following a use of heating devices, the incidence has slightly dropped in the colder months (Carl E. Hunt. 2002).

Measures to reduce the risk of SIDS

As the exact mechanism by which SIDS occurs and the entire risk factors responsible are not known, SIDS cannot be completely prevented.  The respiration pattern and the cardiac functions cannot be constantly monitored to predict this condition and prevent it.  However, several conditions such as obstructive apnea, decreased oxygenation, etc can be identified and prevented appropriately.  Identifying the prolong QT interval may help in predicting the condition, but it may not be practical (Carl E. Hunt. 2002).  Certain guidelines suggested by the AAP may help in the reducing risk of developing SIDS.

The child should be placed in a supine position
Infants can be put to sleep in a safety crib
Infants should never be placed to sleep alongside a child or an adult
It is not advisable to place the child to sleep on sofas or soft surfaces
All soft materials that could obstruct the child’s breathing should be removed
It is advisable not to sleep next to an infant
Smoking, alcohol and drug use by the mother may harm the fetus during pregnancy and increase the risk of developing SIDS
Drugs and tobacco smoking should not be utilized during the postnatal period
Extreme of temperature (too hot or too cold) should be avoided in the environment of the child
The room that the child is sleeping in should be comfortable enough for an adult
Prenatal and postnatal disorders should be given immediate medical attention
Restrictive devices should not be used on the infants
Infants who are at a grave risk of developing SIDS may require the use of cardiac and respiratory monitoring devices
The child can be given a pacifier as it lowers the risk of developing SIDS.  However, this should not be forced on the child.
The Mother should not fear the development of flat spots on the child (especially when the child constantly sleeps on the back) as these slowly begin to disappear once the child begins to grow up.  For sometime, the child can be kept to sleep on the tummy, but his should be done under close observation.