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Upon completion of this self-study module, you should be able to:

  • Define an Apparent Life-Threatening Event (ALTE)
  • Describe how to develop an initial impression for an infant presenting to the emergency department with an ALTE
  • List the critical diagnoses associated with an ALTE
  • Describe the laboratory tests and radiological imaging used for evaluating an infant with a suspected ALTE
  • Discuss appropriate treatment and disposition of an infant diagnosed with an ALTE


An apparent life-threatening event (ALTE) refers to an acute event involving changes in an infant’s breathing pattern, appearance, and/or behavior. The 1986 National Institutes of Health and Consensus Development Conference on Infantile Apnea and Home Monitoring 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. In some cases, the observer fears that the infant has died.”1 The estimated incidence of ALTEs ranges from 0.58 – 2.46 per 1,000 live births, though this may  underestimate the actual incidence.2, 3 In children under 1 year of age, ALTEs account for < 1% of Emergency Department visits.4 The majority of cases occur in children less than 2 months of age. 5

It is important to note that an ALTE is a diagnosis based on a constellation of symptoms. The underlying etiology may not be identified in almost half of all cases. Though there are a broad array of underlying associated etiologies (see Table 1), the most common underlying etiologies associated with ALTEs include: gastro-esophageal reflux (GERD), seizures, and lower respiratory infections.6

Table 1. Differential Diagnosis for an Apparent Life-Threatening Event (ALTE)

General Category or SystemSpecific Etiologies
GastrointestinalGERD, volvulus, intussusception, swallowing abnormalities
NeurologicAfebrile seizures, febrile seizure, intracranial bleed, CNS infection, vasovagal reflexes, hydrocephalus, Budd-Chiari malformation, hindbrain malformation, brainstem malformation, CNS malignancy, ventriculoperitoneal shunt malfunction
RespiratoryBreath-holding spells, laryngotracheomalacia, prematurity, central hypoventilation, vocal cord abnormalities, respiratory syncytial virus/bronchiolitis, pertussis, pneumonia, foreign body aspiration, croup
CardiovascularDysrhythmias, congenital heart disease, cardiomyopathy, myocarditis
MetabolicInborn errors of metabolism, thyroid disorders, hypoglycemia
RenalElectrolyte abnormalities (hypocalcemia, hypomagnesemia, hyponatremia), urinary tract infections
InfectiousSepsis, CNS infections (meningitis, encephalitis), respiratory infections (bronchiolitis, croup, pertussis, pneumonia), UTI
Non-accidental TraumaMunchausen syndrome by proxy, suffocation, abusive head trauma, shaken baby syndrome
ToxicologicalAccidental drug ingestions, carbon monoxide, other toxic ingestions/exposures

Initial Actions and Primary Survey

What initial actions should occur in the Emergency Department (ED) for an infant with a suspected ALTE? First and foremost, the patient must be rapidly assessed for cardiovascular and respiratory stability. This is accomplished by forming an initial impression and performing a primary assessment. Both are discussed below.

Initial Impression

The emergency assessment of any potentially ill infant, including those with a possible ALTE, starts with the initial impression. This initial impression is an observational assessment or “first look impression” based on the visual and auditory presentation of the patient when first encountered, and it precedes the ABCDEs of the primary assessment. The Pediatric Assessment Triangle (PAT) is a tool designed to provide health care professionals a standardized means to generate the initial impression of an ill infant or child.7 It is composed of 3 components: work of breathing, circulation to the skin, and appearance. Characteristics of each PAT component allow a health care professional to quickly assess if the component is normal or abnormal (see Table 2). Once each component is assessed, combination of the 3 provides a picture, or initial impression, of the patient’s cardiopulmonary and central nervous system status. The initial impression is not designed to provide a diagnosis, rather it identifies the general category of physiologic derangement and severity, and provides a point from which to initiate critical interventions.

Table 2. Components of the Pediatric Assessment Triangle

Pediatric Assessment Triangle (PAT)
ComponentCharacteristicsSample Abnormal Findings
Work of Breathing·         Abnormal airway sounds


·         Abnormal positioning

·         Presence of retractions

·         Stridor, grunting


·         Sniffing position

·         Supraclavicular or substernal retractions

Circulation to Skin·         Pallor


·         Mottling

·         Cyanosis

·         Pale skin


·         Irregular patchy skin appearance

·         Blue appearance of skin and/or mucous membranes

Appearance·         Tone


·         Interaction

·         Consolable

·         Gaze

·         Cry

·         Lack of spontaneous movement


·         Does not interact

·         Won’t stop crying with comforting

·         Does not track or make eye contact

·         Weak cry

Derived from: Dieckman RA, Brownstein D, Gausche-Hill M. The Pediatric Assessment Triangle: A Novel Approach for the Rapid Evaluation of Children. Pediatric Emergency Care 2010: 26; 312-315.

Primary Assessment

The primary assessment is a structured physical assessment that proceeds in a specific order (see Table 3).

Table 3. Components of the Primary Assessment

Primary Assessment
A (Airway)Assess patency – evaluate for obstruction, partial obstruction, pooling of secretions or blood
B (Breathing)Assess respiratory rate, breath sounds with auscultation, oxygen saturation



C (Circulation)Assess heart rate, pulse quality (distal and proximal), capillary refill time, blood pressure
D (Disability)Assess level of consciousness, motor activity, pupillary response



E (Exposure)Appropriate exposure of patient is necessary for complete assessment




As described earlier, an ALTE consists of some combination of apnea (usually central), color change (usually cyanotic or pallid, can be plethoric), and loss of muscle tone. The episode is typically frightening to the observer, and may prompt observer attempts to resuscitate the infant. Often, the infant will be asymptomatic on arrival to the ED. If the initial impression and primary assessment reveal an apparently asymptomatic infant in no distress, efforts should focus on a detailed history to identify all aspects of the episode.  As apnea is a central component of the defining characteristics of an ALTE, it is important to understand its definition. Infant apnea is defined as, “an unexplained episode of cessation of breathing for 20 seconds or longer, or a shorter respiratory pause associated with bradycardia, cyanosis, pallor, and/or marked hypotonia.”

Following a clear description of the apnea component, other pertinent questions include:

  • When did the episode occur?
  • Who witnessed the episode?
  • What were the events immediately preceding the episode?
  • When was the last feeding?
  • Did the infant have any symptoms prior to the episode?
  • Was the infant at his/her baseline state of health prior to the episode?
  • What did the episode look like?
  • Where there any color changes? Where?
  • How long was the episode?
  • What (if any) interventions did the observer perform?
  • What happened, or how did the infant appear, immediately after the episode?

Several predictors have been identified that carry a risk for subsequent ALTEs or significant underlying diagnoses.9 These include prematurity, multiple ALTEs, suspected child maltreatment, suspected seizures, and upper respiratory symptoms. Questioning to identify these predictors must be included in the evaluation. Finally, the history should include a thorough evaluation of prenatal, birth, past medical, social, and family history.

Once the initial impression, primary assessment, and history are completed, a thorough physical examination with particular attention to the cardiovascular, respiratory, and neurological systems, and signs suggestive of child maltreatment, should be conducted. The vital signs (including oxygen saturation) should be carefully reviewed for any abnormalities. Signs suggesting an underlying etiology or predictors of subsequent events (see Table 4) must be noted and evaluated. Height, weight, and head circumference measurements should be plotted on appropriate growth charts. The developmental stage should be assessed.

Table 4. Specific underlying associated etiologies for an ALTE, and associated signs

General Category or SystemSpecific Etiologies and Associated Signs
GastrointestinalGastroesophageal reflux


·         Spitting up

·         Choking episodes

·         Poor weight gain


·         Bilious emesis


·         Vomiting

·         Bloody stools



·         Altered level of consciousness

·         Eye deviation

·         Abnormal tone

·         Rhythmic, repetitive motor activity

RespiratoryRespiratory syncytial virus/bronchiolitis


·         Tachypnea/respiratory distress

·         Costal retractions

·         Cough

·         Fever

·         Wheezing


·         Cough

·         Cyanosis

·         Respiratory distress

·         Post-tussive emesis



·         Tachycardia

·         Bradycardia

Congenital heart disease

·         Central cyanosis

·         Diaphoresis

·         Murmur



·         Altered level of consciousness



·         Altered level of consciousness

·         Seizures

Urinary tract infection

·         Fever

·         Vomiting



·         Pallor



·         Fever

·         Hypothermia

·         Lethargy

CNS infections (meningitis, encephalitis)

·         Fever

·         Hypothermia

·         Lethargy/altered level of consciousness

·         Petechial rash

Non-accidental Trauma·         Bulging anterior fontanel


·         Altered level of consciousness

·         Bruising

·         Specific injury patterns (e.g. specific shape of bruises, immersion injuries)

·         Injuries that are not consistent with infants developmental stage

ToxicologicalToxic ingestions/exposures


·         Lethargy/altered level of consciousness

·         Tachycardia or bradycardia (depending on toxic exposure)

Diagnostic Testing

If the history and physical examination suggest a likely underlying etiology for the ALTE, diagnostic studies should be targeted toward the suspected entity. Symptoms of a respiratory tract infection should prompt a chest X-ray plus testing for respiratory syncytial virus and Bordetella pertussis. Suspicion for non-accidental trauma necessitates a head CT and skeletal survey. Concerns for cardiovascular disease require a chest X-ray and electrocardiogram in the ED, and likely other studies as an inpatient (e.g. an echocardiogram). Fever, lethargy, and other signs and/or symptoms suggesting an infectious etiology should be evaluated according to the appearance and age of the infant. Diagnostic tests may include a complete blood count with differential, blood cultures, urinalysis, urine culture, CSF for analysis and culture, and if a respiratory component is present, a chest X-ray plus testing for respiratory syncytial virus and Bordetella pertussis. Evaluation for potential toxic ingestions, in addition to serum electrolytes, BUN, creatinine, and glucose, requires a urine drugs of abuse screen and serum ethanol level.

In the absence of an underlying cause based on the history and physical examination, the laboratory and imaging evaluation of an infant with a suspected ALTE is relatively broad and there is no consensus as to what should be included. Common diagnostic studies include: a complete blood count, serum glucose and electrolytes, blood urea nitrogen (BUN), creatinine, calcium, magnesium, a chest X-ray, and an electrocardiogram. Some algorithms would also recommend including testing for respiratory syncytial virus and Bordetella pertussis, C-reactive protein, an arterial blood gas, urine toxicology screening, an EEG, and imaging of the head.


Initial treatment in the ED should address any potential or identified life threatening conditions. Cardiovascular monitoring (heart rate and blood pressure) and continuous pulse oximetry should be initiated, and vascular access should be obtained.  If the patient is stable and in no obvious risk for immediate deterioration, subsequent treatment should target suspected or identified underlying etiologies for the ALTE. Infants diagnosed with an ALTE that are asymptomatic and do not have an identifiable underlying etiology in the ED should be admitted for observation and further evaluation. It is important to note that a significant proportion of infants (12-13.6%) admitted for an ALTE may have a recurrent significant episode or ALTE during the admission, and most of these will occur within the first 24 hours of admission.11, 12  Admission provides an opportunity to conduct other potential diagnostic testing not immediately available in the ED (e.g. pH probes and upper gastrointestinal series to evaluate for GERD), and to observe the patient for dysrhythmias, other abnormalities, or subsequent ALTEs.

Pearls and Pitfalls

  • Recognize that an ALTE is composed of a constellation of symptoms including apnea, color change, and changes in muscle tone.
  • Understand that many infants presenting to the ED following an ALTE will appear asymptomatic; this does not mean a significant event did not occur.
  • There is still the potential for a serious underlying etiology in the well appearing infant that had an ALTE.
  • The most common underlying etiologies associated with ALTEs include GERD, seizures, and lower respiratory infections.
  • Predictors for subsequent ALTEs or a significant underlying diagnosis include prematurity, multiple ALTEs, suspected child maltreatment, suspected seizures, and upper respiratory symptoms.


  1. National Institutes of Health Consensus Development Conference on Infantile Apnea and Home Monitoring, Sept 29 to Oct 1, 1986. Pediatrics 1987; 79: 292-299.
  2. Kiechl-Kohlendorfer U, Hof D, Peglow UP, Traweger-Ravanelli B, Kiechl S. Epidemiology of apparent life threatening events. Arch Dis Child 2005; 90: 297.
  3. Semmekrot BA, van Sleuwen BE, Engelberts AC, et al. Surveillance study of apparent life-threatening events (ALTE) in the Netherlands. Eur J Pediatr 2010; 169: 229-36.
  4. Davies F, Gupta R. Apparent life threatening events in infants presenting to an emergency department. Emerg Med J 2002; 19: 11-16.
  5. Esani N, Hodgman JE, Ehsani N, Hoppenbrouwers T. Apparent life-threatening events and sudden infant death syndrome: comparison of risk factors. J Pediatr 2008; 152: 365-370.
  6. McGovern MC, Smith MB. Causes of apparent life threatening events in infants: a systematic review. Arch Dis Child 2004; 89: 1043-1048.
  7. Dieckman RA, Brownstein D, Gausche-Hill M. The Pediatric Assessment Triangle: A Novel Approach for the Rapid Evaluation of Children. Pediatric Emergency Care 2010; 26: 312-315.
  8. Committee on Fetus and Newborn, American Academy of Pediatrics. Apnea, sudden infant death syndrome, and home monitoring. 2003; 111: 914-917.
  9. Tieder JS, Altman RL, Bonkowsky JL, et. al. Management of Apparent Life-Threatening Events in Infants: A Systematic Review. J Pediatr 2013; 163: 94-99.
  10. McGovern MC, Smith MB. Causes of apparent life threatening events in infants: a systematic review. Arch Dis Child 2004; 89: 1043-1048.
  11. Santiago-Burruchaga M, Sánchez-Etxaniz J, Benito-Fernández J, et al. Assessment and management of infants with apparent life-threatening events in the paediatric emergency department. Eur J Emerg Med 2008; 15: 203-208.
  12. Al-Kindy HA, Gélinas JF, Hatzakis G, Côté A. Risk factors for extreme events in infants hospitalized for apparent life-threatening events. J Pediatr 2009; 154: 332-337.


Apparent Life-Threatening Event (ALTE)

Authors: Todd Wylie, M.D., Assistant Professor, Department of Emergency Medicine, University of Florida College of Medicine – Jacksonville

Stefani Ashby, M.D., Pediatric Emergency Medicine Fellow, Department of Emergency Medicine, University of Florida College of Medicine – Jacksonville

Editor: S. Margaret Paik, MD, FAAP FACEP , The University of Chicago