Chapter XIV.13. Apparent Life-Threatening Events and Sudden Infant Death Syndrome
Kristyn M. Nishimoto, MD, FAAP
May 2013

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The editors and current author would like to thank and acknowledge the significant contribution of the previous author of this chapter from the 2004 first edition, Dr. Mary Elaine Patrinos. This current second edition chapter is a revision and update of the original authorís work.

Case #1

A 2 month-old male infant presents to the emergency department (ED) via ambulance in full arrest. On the day of presentation, his mother had left him with a babysitter. After a feeding, the babysitter had put him down to sleep. When she checked on him approximately 30 minutes later, she found him pale, not breathing, and limp. She called 911 and began attempts at CPR. En route, CPR was continued and the patient was intubated, an intraosseous line was placed, and two doses of epinephrine were administered.

Past Medical History: The patient was born term via spontaneous vaginal delivery with a birth weight of 3.4 kg (7 lbs 8 oz). There were no complications and he was discharged home from the hospital with his mother on day of life 2. Since then he has been well.

Exam: Vital Signs T 35 degrees C (95 degrees F), pulse and chest rise with CPR, without CPR apneic and pulseless. The infant is mottled without spontaneous movements. Pupils are fixed and dilated.

Clinical Course: Resuscitation is continued in the ED. There is no response to these measures and the infant is pronounced dead after 30 minutes.

Case #2

A 2 month-old female infant presents to the ED after her mother noted that she appeared to stop breathing at home after a feeding. This episode lasted about 10 seconds and the patient appeared to turn blue around the mouth, prompting her mother to call 911. When EMS arrived, the patient appeared well but due to her mother's concerns she was brought to the emergency department for further evaluation.

Past Medical History: The patient was born term via spontaneous vaginal delivery with a birth weight of 3.4 kg (7 lbs 8 oz). There were no complications and she was discharged home from the hospital with her mother on day of life 2. Since then she has been well.

Exam: Vital Signs T 37 degrees C (98.6 degrees F), pulse 140, respirations 24, BP 80/50. The infant appears well, with a normal physical exam.

Clinical Course: The patient remains well appearing in the ED without any abnormalities in her vital signs. She is admitted to the hospital for further observation and monitoring.


SIDS is defined as infant deaths that cannot be explained after a thorough case investigation, including a scene investigation, autopsy, and review of the clinical history. After the scene investigation, though, it appears that many of these deaths are secondary to accidental suffocation or unknown cause, leading to the new broader nomenclature of sudden unexpected infant death (SUID) or sudden unexpected death in infancy (SUDI). SUID is used to describe any sudden death, whether explained or unexplained (including SIDS) that occurs during infancy.

SIDS is suspected when a previously healthy infant appears to have died during sleep. This event will typically occur at home. The infant will often have a normal feeding prior to being placed to sleep. No cry is typically heard and the infant is found in the same position in which he or she had been placed to sleep. Resuscitation may be initiated at the scene but ultimately the infant is pronounced dead.

Every year in the United States, more than 4,500 infants die suddenly of no immediately obvious cause. Approximately half of these SUIDs are due to SIDS, which is the third leading cause of mortality among infants 1 to 6 months of age in the United States. The peak incidence is between 2 and 4 months, with approximately 90 percent occurring before 6 months. In 1994, the Back to Sleep campaign was initiated with a steady decline in deaths until 2000. However, since 2001, the SIDS rate has remained constant although racial and ethnic disparities exist, with African-American infants and American-Indian/Alaska Native infants having higher mortality rates.

SUIDs may be found to be secondary to suffocation, asphyxia, entrapment, infection, ingestions, metabolic diseases, arrythmia-associated cardiac channelopathies, and trauma (accidental or non-accidental). SIDS, on the other hand, is a diagnosis of exclusion. It is considered to be a multifactorial condition in that the combination of a critical developmental period, intrinsic vulnerability (possibly dysfunctional and/or immature cardiorespiratory and/or arousal systems) and exogenous stressors (prone sleep position, overbundling, airway obstruction) lead to a failure of protective responses. This results in progressive asphyxia, bradycardia, hypotension, metabolic acidosis, and ineffectual gasping, that ultimately lead to death. At this time it is unclear what mechanisms are responsible for the intrinsic vulnerability. Associations that have been found include brainstem abnormalities involving the medullary serotonergic 5-hydroxytryptamine system and tobacco smoking, as well as mutations in the cardiac sodium or potassium channel genes that result in long QT syndrome.

As currently there is no definitive test to diagnose SIDS, an infant death should be determined to be attributable to SIDS when all of the following are true:

1. A complete autopsy is performed and findings are compatible with SIDS.

2. There is no evidence of acute or remote inflicted trauma, significant bone disease, or significant and contributory unintentional trauma.

3. Other causes and/or mechanisms of death are sufficiently excluded, including meningitis, sepsis, aspiration, pneumonia, myocarditis, trauma, dehydration, fluid and electrolyte imbalance, significant congenital defects, inborn metabolic disorders, asphyxia, drowning, burns, or poisoning.

4. There is no evidence of toxic exposure to alcohol, drugs, or other poisoning.

5. Thorough death and/or incident scene investigation and review of the clinical history reveal no other cause of death.

Investigations are conducted by a multi-disciplinary team consisting of first-responders, child welfare or child protection services, physicians, pathologists, law enforcement, for all unexplained infant deaths. First-response teams are trained to make observations of the scene (such as position of infant, marks on the body, position of clothing and bedding) and to distinguish between normal postmortem findings and those that may be attributable to abuse. Guidelines are also available for investigation of the circumstances of SUIDs. As parents are typically distressed, those involved in the investigation should be compassionate, empathetic, supportive, and non-accusatory. The majority of infants who die from SIDS are not victims of child abuse, with estimates ranging from about 1 to 5 percent. During the investigation, there are certain circumstances that should raise concern for intentional suffocation:

1. Previous recurrent cyanosis, apnea, or apparent life-threatening event (ALTE) while in the care of the same person

2. Age of death older than 6 months

3. Previous unexpected or unexplained deaths of 1 or more siblings

4. Simultaneous or nearly simultaneous death of twins

5. Previous death of infants under the care of the same unrelated person

6. Evidence of previous pulmonary hemorrhage

During prenatal counseling and well-child checks, physicians should provide anticipatory guidance to families to prevent SIDS and SUIDS. The current American Academy of Pediatrics (AAP) Policy Statement on SIDS and Other Sleep-Related Infant Deaths recommends:

1. Infants should be placed in a supine sleep position, not prone or side-sleeping

2. Use a firm sleep surface

3. Room-sharing without bed-sharing, especially if there are multiple bedsharers or when the parents has consumed alcohol

4. Keep soft objects and loose bedding out of the crib

5. Cigarette smoking, alcohol and illicit drug use should be avoided

6. Consider offering a pacifier at nap time and bedtime, after breastfeeding is well established

7. Overheating should be avoided

8. Home cardiorespiratory monitors should not be used to prevent SIDS

The emphasis of supine sleep position in the Back to Sleep campaign has drastically decreased the number of deaths due to SIDS. However, current efforts are still being made to target this message to populations with higher incidences, such as African-Americans and other infant caregivers such as babysitters and daycare personnel. The sleep environment is also important, with attempts made to minimize the risk of suffocation from bedding and other individuals. The AAP encourages breastfeeding, and infants may be brought to the bed for feeding and comforting but should be returned to their own crib or bassinet when the parent is ready to return to sleep. It also does not recommend the use of positioning devices, drop-down cribs, or bumper pads. It does note that prone positioning is acceptable when the infant is awake and supervision available to promote motor development and minimize positional plagiocephaly (tummy time).


ALTEs previously were considered to be aborted SIDS or near-miss SIDS. However, in 1986, the National Institutes of Health consensus working group for SIDS formally defined an ALTE as an episode that is frightening to the observer and that is characterized by some combination of apnea (central or occasionally obstructive), color change (usually cyanotic or pallid but occasionally erythematous or plethoric), marked change in muscle tone (usually marked limpness), choking, or gagging. Periodic breathing, in which three or more pauses occur, each lasting more than three seconds but with less than 20 seconds of normal respiration between pauses, is normal. In contrast, pathologic apnea occurs when the respiratory pause lasts for 20 seconds or more, and is accompanied by bradycardia, cyanosis, hypotonia, or other signs of compromise. In addition, apnea of prematurity is periodic breathing with pathologic apnea associated with preterm delivery. It usually resolves by 34 to 36 weeks gestation but may continue for a few weeks beyond term gestation. It is due to an immature central respiratory center control, as opposed to obstructive apnea, which occurs secondary to conditions such as craniofacial abnormalities or hypotonia. Apnea of infancy is usually reserved for infants who present with an ALTE in whom no plausible etiology is identified.

ALTEs are relatively uncommon, with incidence between 0.6 and 2.5 per 1000 lives births. Most occur in children younger than one year of age, with a peak incidence between one week and two months of age. Those who are born premature are at increased risk for an ALTE but not for SIDS.

ALTE does not refer to a single diagnosis, but rather a clinical condition. There are many potential causes for ALTE, but only approximately 50 percent of cases will result in an identifiable diagnosis. The most common diagnoses include gastroesophageal reflux, lower respiratory tract infection, and seizure. Infants older than two months of age with an ALTE and those with recurrent ALTEs are more likely to have significant disorders.

Table 1: Differential Diagnosis of ALTE:

1. Gastrointestinal (GI) (up to 50 percent of diagnosed cases): gastroesophageal reflux, gastric volvulus, intussusception, swallowing abnormalities, other GI abnormalities

2. Neurologic (30 percent): seizure disorder, febrile seizure, central nervous system (CNS) bleeding, neurologic conditions affecting breathing, CNS infection, malignancy

3. Respiratory (20 percent): respiratory compromise from infection (i.e. RSV, pertussis, pneumonia), obstructive sleep apnea, conditions affecting respiratory control (i.e. prematurity, central hypoventilation), airway obstruction due to congenital abnormalities, foreign-body aspiration

4. Cardiac (5 percent): arrhythmia - especially prolonged QT syndrome, congenital heart disease, myocarditis, cardiomyopathy

5. Metabolic abnormalities (less than 5 percent): inborn errors of metabolism, endocrine or electrolyte disorders

6. Child abuse (less than 5 percent): smothering (unintentional or intentional), Munchausen syndrome by proxy

7. Other: sepsis, food allergy, anaphylaxis, medication (prescription, over the counter, herbal remedies)

A thorough history and physical exam is key for trying to elicit the cause of an ALTE. This can help distinguish more concerning events, such as sepsis or arrhythmias, that require further workup and treatment from less concerning events, such as periodic breathing, non-malignant choking or gagging associated with feeding, or non-pathologic muscular jerking. Important questions to ask in the history are detailed in Table 2. If the patient is symptomatic, immediate assessment should also include ABCs (airway, breathing, circulation). Physical exam should include growth parameters, dysmorphic features, cardiovascular and neurologic exam, and signs of trauma.

Table 2: Important Questions to Ask

1. Events surrounding the ALTE: What was the child doing before the event (i.e. sleeping or awake, position of infant, feeding)? Fever or other symptoms? Who observed the event? How long did the event last? Was intervention (i.e. gentle stimulation, CPR) required to stop the event? Apneic event and for how long? Color changes and location on the body? Rhythmic movements or seizure-like activity? Altered mental status or change in muscle tone? What happened after the event?

2. Medical history: History of ALTE? Medical conditions such as prematurity, seizures, or congenital heart disease?

3. Medication history: What medicines does the child take? What other medications are in the home? Alternative or complementary medications?

4. Family history: Seizures, cardiac conditions, genetic or metabolic disorders, neonatal and child deaths, SIDS?

5. Social history: Who was caring for the child at the time of the event? Inconsistencies within the story? Social stressors or recent life changes? Infectious exposure?

Routine admission for patients for a thorough evaluation remains controversial; but admission for an observation period is reasonable. Those that present with severe episodes, for example those requiring CPR, or with abnormal results on history and physical exam, should be admitted for further evaluation. Hospitalization allows the physician to monitor the infant and provide direct observation for any parental or social issues. However, parents should also be informed that it is unlikely that a treatable cause will be identified. In addition, for those infants with a reassuring history of a benign event and normal physical exam, it may be possible to discharge them home after a period of observation if adequate follow-up can be assured.

As there is no evidence that ALTEs are precursors to SIDS, the AAP does not recommend that infant home monitors routinely be used to prevent SIDS. However, monitors may be warranted for infants who are technology dependent, have unstable airways, have rare medical conditions affecting regulation of breathing, or have symptomatic chronic lung disease. This is due to the high rate of false alarms, parental anxiety, inappropriate use of monitors, and the lack of proven efficacy in the prevention of death. The National Institute of Child Health and Development Cooperative Epidemiological Study of SIDS cases found that only 2 to 4 percent had a record of apnea of prematurity and less than 7 percent had a history of ALTE. All caregivers should be encouraged to become educated in CPR techniques.


1. True or False: All ALTE episodes are thought to be precursors to SIDS.

2. Intentional suffocation should be considered as a possibility of a SUIDS death when:
. . . . . a. The infant is younger than 6 months of age
. . . . . b. Previous ALTEs have occurred under the care of different caregivers
. . . . . c. Previous death of another family member under the care of the same unrelated caregiver
. . . . . d. No evidence of intrapulmonary hemorrhage
. . . . . e. No family history of SIDS or ALTE episodes

3. True or False: Co-sleeping is acceptable if a mother is breastfeeding.

4. True or False: Home apnea monitors do not prevent SIDS


1. Task Force on Sudden Infant Death Syndrome. SIDS and Other Sleep-Related Infant Deaths: Expansion of Recommendations for a Safe Infant Sleeping Environment. Pediatrics 2011;128(5):1030-1039.

2. Centers for Disease Control and Prevention. Sudden Unexpected Infant Death and Sudden Infant Death Syndrome. Updated March 7, 2013. Accessed March 12, 2013.

3. Hymel KP, National Association of Medical Examiners. Distinguishing Sudden Infant Death Syndrome from Child Abuse Fatalities. Pediatrics 2006;118:421-427.

4. Task Force on Sudden Infant Death Syndrome. Technical Report: SIDS and Other Sleep-Related Infant Deaths: Expansion of Recommendations for a Safe Infant Sleeping Environment. Pediatrics 2011;128(5):e1341-e1367.

5. Little GA, et al. National Institutes of Health Consensus Development Conference on Infantile Apnea and Home Monitoring, Sept 29 to Oct 1, 1986. Pediatrics 1987;79(2):292-299.

6. Hall KL, Zalman B. Evaluation and Management of Apparent Life-Threatening Events in Children. American Family Physician 2005;71:2301-2308.

7. Bonkowsky JL, Tieder JS. A pragmatic approach to ALTEs. Contemporary Pediatrics 2009;26(1):54-63.

8. Brand DA, Altman RL, Purtill K, Edwards KS. Yield of Diagnostic Testing in Infants Who Have Had an Apparent Life-Threatening Event. Pediatrics 2005;115(4):885-893.

9. McGovern MC, Smith MBH. Causes of apparent life threatening events in infants: a systematic review. Arch Dis Child 2004;89:1043-1048.

10. Committee on Fetus and Newborn. Policy Statement: Apnea, Sudden Infant Death Syndrome, and Home Monitoring. Pediatrics 2003;111(4):914-917.

Answers to questions

1.False, 2.c, 3.False, 4.True

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