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Sudden Infant Death Syndrome


Sudden Infant Death Syndrome (SIDS) is marked by the sudden death of an infant less than 1 year of age that cannot be explained until a thorough investigation (autopsy, examination of the death scene, review of the clinical history) is conducted.



When SIDS occurs, one should obtain the following history [7]:

  • When was infant put to bed?
  • How many times was the baby checked and when was the last time
  • What position was the baby in when found unresponsive
  • Did the baby have any health issues prior to death?
  • Did the baby have any history of airway obstruction or breathing difficulties?
  • Did the baby ever have apnea, GERD, or difficulty with feeding?
  • When was the last meal?
  • What was the baby’s color and tone when found?
  • Did anyone perform CPR, how was it done?

Apparent life threatening events (ALTE) may include:

Physical examination

When an infant has died from SIDS, the scene of death needs to be examined for any signs of external airway obstruction, entrapment of the neck or presence of any environmental toxin like carbon monoxide. For infants who are found alive and brought to the Emergency room, most will be lethargic and not show any signs of outward distress. In more than half of these infants, the physical exam is normal. In the remaining infants one may find fever or signs of an infection. The work up of a child with suspected SIDS depends on the physical medical judgment and expertise. The history of the child may suggest that the apnea may be obstructive central or mixed.

  • The child must be examined without any clothing. The CNS, and cardiac system must be thoroughly examined and a search for congenital defects must be looked for. Presence of irregular respiratory rate or hypotonia may indicate an acute apnea event.
  • Truncal bruising and other lesions
  • The child must be examined for the following to exclude child abuse and other non-accidental causes
  • Look for bruising over bony prominences, check for age of bruising by looking at color. Purple or red color may signal that a bruise occurred recently. A yellow bruise indicate that the bruise is at least 18 hours old
  • Check the skin for bite or pinch marks, scalds, burns (e.g. from cigarettes)
  • Check the extremities, skull and ribs for fractures
  • Look for pupillary changes and response to light to assess presence of elevated intracranial pressure
  • Perform a fundoscopy exam to look for retinal hemorrhages, because they are often associated with a shaken baby syndrome
  • Look in the nose and mouth for any bleeding because in child abuse this is not an uncommon event.

All the findings from a clinic exam have to be photographed and recorded, it is important to note that if any dead infant arrives to the ED, the physician should call the coroner first without manipulating the body. The autopsy is vital to rule out SIDS and other causes of death. Manipulation of the body can distort signs and lead to false conclusions.

Autopsy findings

The autopsy of an infant suspected of SIDs should be thorough and usually includes the following:

  • Signs of hydration
  • Failure to thrive or adequately nourished
  • Presence of any obvious external trauma
  • Look for any congenital defects that may have contributed to death
  • Presence of Petechiae
  • Microscopic examination for inflammatory changes or signs of congestion of organs

SIDS versus infanticide

Whenever a death in an infant occurs, infanticide has to be ruled out.

Findings that raise the suspicion of child abuse are as follows:

  • History that is not consistent with SIDs or is very vague
  • The time to death after putting infant to bed is prolonged
  • Age of death is greater than 6 months
  • Unexplained and unexpected death of the infant
  • Prior involvement with child protective services, social workers or law enforcement.
  • Family or caregiver has a history of violence and/or has been arrested in the past.
  • Presence of neglect or malnutrition
  • Presence of cutaneous injuries, trauma on the face and scalp, fractures and anogenital injuries

Features suggestive of SIDS include the following:

  • A healthy infant placed in the crib after feeding and found motionless
  • Silent death
  • CPR not successful
  • Age at death is less than 7 months

However, the absence of any clinical features does not mean that the death was due to natural causes. There are cases where a hand or a pillow has been used to smother the child, called gentle battering. In some cases of SIDS, the infant may have clenched fists at birth signalling terminal motor activity.

It is vital not to jump to conclusions as misinterpretation of post mortem changes that are seen in SIDS related death like anal dilatation or post-mortem lividity.

  • More prolonged attacks, and especially those associated with pallor, blueness or a long recovery period are more important.[health24.com]
  • A respiratory pause is abnormal if it is prolonged ( 20 sec) or if it is associated with cyanosis; abrupt, marked pallor; hypotonia; or bradycardia.[emedicine.com]
Abnormal Breathing
  • It should be emphasised, however, that the great majority of babies dying of “cot death” do so without any previously recognised apnoeic episodes, or abnormal breathing patterns.[health24.com]
  • […] that both have occurred. 112 – 115 Congenital PWS is generally thought to be caused by in utero or intrapartum molding and, therefore, is often associated with multiple births or birth injury. 116, 117 Infants born preterm may develop plagiocephaly or dolichocephaly[pediatrics.aappublications.org]


Approach considerations

In most cases, the infant is dead at the scene, but if there is any sign of life, EMS should be called and the infant transported to the nearest ED. In many jurisdictions, an autopsy is usually performed when the cause of death is unknown and sudden. There are national guidelines in many countries on reporting of SIDS to the coroner.

A diagnosis of SIDS is only made by excluding all other possible disorders. Information collected at the scene and the infant’s medical history is vital to make the diagnosis. During an autopsy, images of the organ systems are obtained. In addition, Tissue is obtained for microbiology, biochemistry, toxicological analysis and drugs. Tissues are also analyzed under a microscope to ensure that there are no structural causes that may account for the sudden death. A diagnosis of SIDS is made only when all other organic causes have been excluded .

In all surviving infants, more exhaustive workup is done that includes the following:

  • Immediate bedside glucose
  • Complete blood count
  • Electrolyte levels to rule out hypokalemia, hypocalcemia or hyperkalemia
  • Urine tests
  • Liver and renal function
  • Blood and urine cultures
  • Arterial blood gas to determine pH and oxygenation status and metabolic acidosis
  • Images of the chest and brain
  • ECG
  • EEG if there is suspicion of seizures
  • Lumbar puncture is done as part of the septic work up, even in the absence of neurological symptoms
  • Drug screen for illicit drugs, prescription medications and other household poisons
  • Septic workup-panculture. In young infants RSV, chlamydia and pertussis should be considered


To rule out skeletal trauma, whole body X-rays must be obtained. These images should be checked to look for metaphyseal fractures that are often seen in cases of nonaccidental trauma like child abuse. Anytime a fracture is seen in a child less than 12 months of age child abuse should be suspected. Even during CPR, it is almost impossible to fracture the ribs of an infant. Anterioposterior and lateral soft tissue films of the cervical spine should be obtained to look for obstruction of the upper airways or presence of a foreign body. If child abuse is suspected, a CT scan of the skull is recommended.


From autopsy studies done in infants with a possible diagnosis of SIDS, only 6% of infants have been shown to have an organic cause of death. All these infants has a relevant history of an organic cause. In the absence of suggestive clinical history and absence of any gross abnormalities, histological examination of the brain is rarely productive in determining the cause of death. The yield is improved in infant with a clinical history and evidence of gross brain findings.

The diagnosis of SIDS is made by excluding other potential disorders. The biggest difference in an infant who dies suddenly is child abuse, and hence every effort must be made to ensure that the infant death was not due to harm by the parent or the caregiver. Even though SIDs deaths are much rarer than child abuse cases, the onus is on the healthcare provider to rule it out. Thus, it is vital to obtain a thorough history from the caregiver about the infants present and past illnesses. Child abuse maybe suspected if the history is inconsistent with the physical findings. The physical exam must also be thorough to look for evidence of any intentional trauma.

  • In young infants RSV, chlamydia and pertussis should be considered Imaging To rule out skeletal trauma, whole body X-rays must be obtained.[symptoma.com]
Ventricular Hypertrophy
  • The heart showed right ventricular hypertrophy, a finding consistent with chronic hypoxemia.[ncbi.nlm.nih.gov]


Because the etiology of SIDs is multifactorial, several recommendations have been made to prevent SIDS.[8][9]

  • Always place the infant to sleep in the supine position. Avoid side sleeping as it is not as safe as the supine position.
  • Use a firm mattress and avoid use of soft pillows, quilts or comforters under a sleeping infant. A firm crib mattress should be covered by a sheet.
  • If bumpers are used to protect against crib trauma, they should be well secured, thin and firm. Avoid use of loose sheets and blankets. If a blanket is used, it should be securely tucked under the mattress.
  • Do not smoke during pregnancy. Avoid exposure to second hand smoke.
  • The infant may sleep in the same room as the mother but not in the same bed. After breast feeding, the infant should be returned to his or her own crib.
  • Never sleep with an infant on a couch or a sofa and do not share the infant’s cribs with other children.
  • Consider use of a pacifier at bedtime. However, prolonged use should be avoided as pacifiers can cause dental malocclusion, otitis and other non-nutritive sucking behavior.
  • The bedroom temperature should be comfortable and not too hot. Do not over bundle the infant with blankets.
  • Avoid purchasing commercial devices to lower the risk of SIDs. Most of these devices have not been tested and lack scientific validity.
  • Do not use home monitors to lower risk of SIDs unless specified by the healthcare provider.
  • Always tell whoever is looking after the infant that at sleeping time, the infant should always be in the back position.

The treatment of SIDs requires providing emotional support for the parents. It is important to note no diagnosis should be offered to the parent until after the autopsy is done. SIDs cases have frequently been followed by litigation by caregivers when a wrong diagnosis is given and child abuse is missed. In cases, where the infant has passed away, a team approach consisting of social workers, healthcare providers, and any relevant religious leader should be present. Telling parents about the death of the infant in an emergency setting is stressful and this is often worsened by feelings of inadequacy or guilt at not having saved the infant.


The prognosis of SIDS has improved over the past 2 decades because of better parental education on how the infant should sleep. The mortality rates have declined but SIDs still continues to occur at a rate of 1 death per every 10,000 births. Because the disorder occurs in apparently healthy infants, it is hard to predict who will develop SIDS.


Many causes of SIDS have been put forward but there is still disagreement as to which is most significant or relevant [3]. Various classifications of risk factors have been developed and the one most widely used is as follows:

  • African American race
  • Apgar score at 5 minutes less than 7
  • Neurological factors (eg, deficiency in asphyxial arousal)
  • Environmental temperature: incidence of SIDs appears to be high in warm internal environments and cold outdoor temperatures.
  • Sleeping prone position
  • Gestational age of less than 37 weeks at birth
  • Infection and suppressed immunity. Various organisms have been found in SIDS infants and in particular RSV, which has the potential to cause apneic episodes [5].
  • Low socioeconomic status
  • Male sex
  • Maternal age younger than 20 years
  • Maternal education level less than 12 years
  • Maternal factors during pregnancy like unwed, drug and alcohol use, anemia, weight gain < 20 lb. during pregnancy, and developing recurrent urinary tract infections.
  • Maternal smoking and illicit drug use during pregnancy
  • Maternal alcohol and caffeine use
  • More than two prior pregnancies
  • Multiple births
  • Not breast feeding
  • Not using a pacifier
  • Very low birth weight (< 1,500 to 2,500 g)


The frequency of SIDS has been declining over the past 2 decades, partly because of more awareness of the disorder and better parent education. However, the disorder is still a leading cause of unexpected deaths in infancy accounting for 30-60% of deaths within the post neonatal period. The one key feature that has led to a reduction in SIDs death is the avoidance of PRONE sleeping. The National institute of Child Health and Human Development has issued a statement saying that supine position can lower the risk of SIDS. Since this statement was introduced in 1992, there has been a significant reduction in infants being placed prone for sleep [4]. Awareness of SIDS over the past 2 decades has led to a significant drop in deaths both in the USA and in most western countries. Currently an incidence of 1 death per 10,000 live births is reported in the USA. Sadly while SIDS is decreasing what is now coming to the forefront is that many of infants deaths previously thought to be SIDs may have been due to child abuse, and the number of cases are on the increase.

Worldwide the rate of SIDS have been dropping because of public health campaigns and education of parents emphasizing the use of supine sleeping positions versus prone. Another modifiable risk factor for SIDS that has recently emerged is tobacco smoke exposure. It is well known that there is a 2-4 fold increase in SIDS in infants whose mother smoke. Unfortunately despite public campaigns, maternal smoking rates have not been declining but in fact increasing.

Other modifiable risk factors which have led to a decrease in SIDS include over bundling or covering the infants head before age of 3 months has been shown to increase risk of SIDS. Another controversial factor that has led to a decrease in SIDS is bed sharing. While bed sharing is more convenient for mothers who breast feed as it also enhances maternal bonding, epidemiological data indicate that bed sharing may be hazardous in certain conditions. There are conflicting reports on bed sharing with mothers who do not smoke and occurrence of SIDS. This risk is increased when there are multiple people sharing the bed, and especially if the individual has consumed alcohol. Finally there is some evidence linking SIDS to the duration of sleep with a partner. More recent studies show that room sharing rather than bed sharing is associated with a decreased risk of SIDS.

The use of pacifiers has been associated with a protective effect against SIDS but the mechanism appears unclear. However, introduction of the pacifier in infants is also associated with dental malocclusion, non-nutritive sucking behavior and a slightly higher risk of otitis media. Initially it was suspected that apnea was the cause of SIDS and hence home apnea monitors were widely sold to parents to prevent SIDS. Unfortunately there is no evidence that home monitors are effective in preventing SIDS. However, some experts recommend use of home apnea monitors in a select group of infants who develop apnea and may have evidence of airway obstruction. So far most studies have refuted the association between SIDS and immunizations.

Recent studies indicate that breast fed infants are more arousable from sleep than those who are not breast fed, suggesting that breast feeding may have a possible protective effect. Unfortunately there is little solid evidence to support that breast feeding is protective. While the habit is beneficial one should not rely on it as a method to prevent SIDS. SIDS generally affects infants between 2-4 months of age and the majority are less than 6 months old. Close to two third of SIDS death are in males. In the USA, SIDS rates are highest in Native American Indians and Alaskan natives followed by African Americans. The reason is believed to be in the fact that the infants in these races, who often tend to sleep in the probe position, may have low birth weight, young maternal age and perhaps high parity.

Sex distribution
Age distribution


The exact cause of SIDS is not known but there are countless theories. Even though many hypotheses have been used to explain SIDS, none has been proven clinically. The overall theme is that there are several factors which interact, resulting in SIDS. These factors include the following:

  • Presence of abnormalities in the central control of the cardiac and or respiratory system
  • Vulnerable infant
  • Infant is at a critical period in the development of his/her CNS homeostatic mechanisms
  • Presence of external or environmental trigger factors (tobacco smoke)
  • Probably genetic factors

In general SIDS rarely occurs in the presence of only one risk factor, but it is more likely to have two or more risk factors present. It is believed that in vulnerable infants, the stressors override the normal defense mechanism and lead to death. Over the years many studies have looked at genes that code for certain neurotransmitters and nerve conduction pathways, but so far no specific gene has been identified [6].

Theories that have been linked to cause of SIDS include the following:


The recommendation for prevention of SIDS is to place the infant supine while sleeping, avoiding maternal smoking, alcohol and use of illicit drugs. The infant should not sleep in the same bed as the caregiver but may sleep in the same room. Use of a firm mattress, adequate temperature control, avoiding over bundling and sharing the infant's crib with other children are other preventive measures.


Sudden infant death syndrome (SIDS) is the death in infants less than 12 months of age. These deaths often occur unexpectedly, suddenly and in most cases, there is no obvious cause. SIDS is the leading cause of sudden infant death in the United States and the diagnosis is only made after a thorough forensic autopsy. The pathogenesis of SIDS is poorly understood. In summary, SIDS most likely occurs in infants who have delayed the development of nerve networks in the brain that play a role in arousal to life threatening events during sleep. In addition, some infants may also have temporary defects in control of the respiratory or cardiovascular system, and the thermoregulation and chemoreceptor sensitivity. The exact anatomical dysfunction in the brain stem is not known but it is believed that it may be a delay in development of mature neuronal connections to the mid-brain. Regardless of the brainstem dysfunction, it is believed that SIDS occurs because the infant’s response to certain stimuli and stress are not well developed or absent. There are now guidelines established for physicians to report all suspected cases of SIDS to the local medical examiner. It is hoped that collection of data from ED physicians will help provide more information about this condition [1] [2].

Patient Information

SIDS is a disorder that leads to unexpected and sudden death of an otherwise healthy infant. The exact cause of SIDS remains unknown but placing the infant on his stomach to sleep is a major risk factor. In most cases, the parent or caregiver reports no problems with the infant and after putting him or her to sleep is later found unresponsive. Numerous hypotheses have been developed and the overall feeling is that the infant has poor development of some reflexes which help fight stress and low oxygen. Other risk factors for SIDS include maternal smoking, drug use, sleeping in the same bed as the infant and over bundling the infant with loose blankets. The risk of SIDS can be decreased by use of a pacifier and placing the child on his or her back during sleep. While the infant should not share the same bed as the parent, the infant can be placed in the same room.



  1. Fleming PJ, Blair PS, Pease A. Sudden unexpected death in infancy: aetiology, pathophysiology, epidemiology and prevention in 2015. Arch Dis Child. 2015 Feb 19.
  2. Hunt CE, Darnall RA, McEntire BL, Hyma BA. Assigning cause for sudden unexpected infant death. Forensic Sci Med Pathol. 2015 Jun;11(2):283-8.
  3. Lagercrantz H. Numerous hypotheses about sudden infant death ... but no impact]. Lakartidningen. 2014 Sep 17-23;111(38):1572-4.
  4. Fleming P, Pease A, Blair P. Bed-sharing and unexpected infant deaths: what is the relationship? Paediatr Respir Rev. 2015 Jan;16(1):62-7.
  5. Alfelali M, Khandaker G. Infectious causes of sudden infant death syndrome. Paediatr Respir Rev. 2014 Dec;15(4):307-11.
  6. Mitchell EA, Krous HF. Sudden unexpected death in infancy: a historical perspective. J Paediatr Child Health. 2015 Jan;51(1):108-12.
  7. Tabor PD, Ragan K. Infant death scene investigation. J Forensic Nurs. 2015 Jan-Mar;11(1):22-7.
  8. Horne RS, Hauck FR, Moon RY. Sudden infant death syndrome and advice for safe sleeping. BMJ. 2015 Apr 28;350:h1989.
  9. Bergman NJ. Proposal for mechanisms of protection of supine sleep against sudden infant death syndrome: an integrated mechanism review. Pediatr Res. 2015 Jan;77(1-1):10-9.

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Last updated: 2019-07-11 20:19