(Brief, Resolved, Unexplained Event)

ByChristopher P. Raab, MD, Sidney Kimmel Medical College at Thomas Jefferson University
Reviewed/Revised Feb 2023
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BRUE (brief, resolved, unexplained event) is an episode of cyanosis or pallor, abnormal breathing, abnormal muscle tone, or altered responsiveness in infants. A previous term for similar events was ALTE (apparent life-threatening event). BRUE is not a specific disorder and is diagnosed only when no other cause is identified for a qualifying event.

BRUE (brief, resolved, unexplained event) is not a specific disorder, it is a term to describe a sudden, brief, and now resolved episode of the appearance of altered hemodynamic status and responsiveness in an infant.

In the 2016 American Academy of Pediatrics guidelines, BRUE replaced the term ALTE (apparent life-threatening event), which was thought to be overly broad and alarming to caregivers (1) and may have resulted in unnecessary medical testing. BRUE is defined slightly differently than previous terms; the diagnosis requires the child to be < 1 year old; the event to have no other likely explanation; and the diagnosis to be based on the clinician’s characterization of features of the event and not on a caregiver’s perception that the event was life-threatening.

Some infants have a transient event involving some combination of altered respiration, consciousness, muscle tone, and/or skin color. This is alarming for caregivers—some of whom may fear that they are observing a life-threatening event and may even begin doing cardiopulmonary resuscitation (CPR). Although a small minority of these infants are found to have a significant underlying disorder, among infants who appear well after this type of episode, a large number do not have recurrences or complications and go on to develop normally (2).

BRUE refers to events lasting < 1 minute in an infant < 1 year of age that are associated with ≥ 1 of the following:

  • Absent, decreased, or irregular breathing

  • Cyanosis or pallor

  • Altered level of responsiveness

  • Marked change in muscle tone (hypertonia or hypotonia)

In addition, infants must otherwise appear well and be back at their baseline state of health after the event. Thus, infants who are febrile, coughing, or showing any signs of distress or other abnormalities are not considered to have had a BRUE.

The term BRUE applies only to events for which there is no underlying cause (hence "unexplained"), which can be determined only after a thorough history and physical examination and sometimes testing and a period of observation. For infants with a similar presentation in whom a cause was identified, clinicians should identify a diagnosis for the episode based on the underlying cause.

Differential diagnosis

BRUE is diagnosed only when there is no explanation for the event. A number of disorders can manifest with similar abnormalities of breathing, responsiveness, tone, and/or skin color. Thus, it is important to search for a cause.

The most common possible causes include

Less common possible causes include

Causes may be genetic or acquired. If an infant is under the care of one person and has repeated episodes with no clear etiology, child abuse should be considered.


  1. 1. Tieder JS, Bonkowsky JL, Etzel RA, et al: Brief Resolved Unexplained Events (formerly Apparent Life-Threatening Events) and evaluation of lower-risk infants. Pediatrics 137(5):e20160590, 2016. doi: 10.1542/peds.2016-0590. Clarification and additional information. Pediatrics 138(2):e20161487, 2016.

  2. 2. McGovern MC, Smith MB: Causes of apparent life threatening events in infants: A systematic review. Arch Dis Child 89(11):1043–1048, 2004. doi: 10.1136/adc.2003.031740

Evaluation of BRUE

Evaluation of infants with any other manifestations besides those defined as BRUE is described elsewhere (see, for example, cough, fever, nausea and vomiting, seizures, and Approach to the Patient With a Suspected Inherited Disorder of Metabolism).


Evaluation of an event initially involves a thorough history, including

  • Observations by the caregiver who witnessed the event, particularly a description of changes in breathing, color, muscle tone, and eyes; noises made; length of episode; and any preceding signs such as respiratory distress or hypotonia

  • Interventions performed (eg, gentle stimulation, mouth-to-mouth breathing, CPR)

  • Prenatal (maternal) or current caregiver use of medications, tobacco, alcohol, or illicit substances

  • Information about the infant’s birth (eg, gestational age, perinatal complications)

  • Feeding habits (whether gagging, coughing, vomiting, or poor weight gain has occurred)

  • Growth and development history (eg, length and weight percentiles, developmental milestones)

  • Prior events, including recent illness or trauma

  • Recent exposure to infectious illness

  • Family history of similar events, early deaths, long QT syndrome or other arrhythmias, or possible causative disorders

Features in the history suggestive of child abuse should be sensitively assessed. Recurrent events that are concerning for abuse include those where the examination findings do not match the history and the event occurs only in the presence of a caretaker.

Because disposition depends in part on family capabilities and resources, it is also important to assess the housing and family situation, the level of caregiver anxiety, and whether the infant has ready access to follow-up medical care.

Physical examination

Physical examination is done to check for abnormal vital signs, respiratory signs, obvious malformations and deformities, neurologic abnormalities (eg, posturing, inappropriate head lag), signs of infection or trauma (particularly including retinal hemorrhage on funduscopy), and indicators of possible physical abuse.

Risk classification

Possible BRUEs are classified as low or high risk based on history and physical examination.

Low-risk infants are those who meet the following criteria:

  • Age > 60 days

  • Gestational age at birth ≥ 32 weeks and post-conceptual age ≥ 45 weeks

  • One event only, no prior BRUE and no cluster of BRUEs

  • No CPR required by trained medical provider

  • No features of concern in history (eg, concern for child abuse, family history of sudden death)

  • Normal physical examination (eg, afebrile, normotensive)

Low-risk infants are very unlikely to have a serious underlying disorder, and the 2016 guidelines recommend few or no interventions other than caregiver education.

High-risk infants include all those who do not meet low-risk criteria. The current guidelines do not contain recommendations for their evaluation and management, so evaluation and management should be based on the history and findings in the infant.


For low-risk infants, guidelines recommend minimal testing. It is reasonable to observe the infant (including monitoring pulse oximetry) in the emergency department or office for a brief period and do 12-lead ECG and testing nasopharyngeal swab for pertussis (culture or PCR). Other tests, including imaging studies and blood tests, are not necessary. Routine hospital admission also is not necessary; however, infants may be hospitalized for cardiorespiratory monitoring if caregivers are extremely anxious or are unable to bring the infant for follow-up in 24 hours.

For high-risk infants, laboratory and imaging tests are done to check for possible causes. Some tests are done routinely and others should be done based on clinical suspicion of a specific etiology of the episode (see table Tests for High-Risk Infants With BRUE), including whether the infant is still symptomatic or has required medical intervention. Infants are often hospitalized for cardiorespiratory monitoring, particularly if they required resuscitation or if evaluation detected any abnormalities.


Treatment of BRUE

  • Caregiver education

  • Close follow-up

  • Treatment of cause if identified

Low-risk infants

Parents and caregivers should be educated about BRUEs and offered training in CPR for infants and in safe infant care. Home cardiorespiratory monitoring is not necessary. Infants should be reevaluated within 24 hours.

High-risk infants

The cause, if identified, is treated.

Guidelines regarding the use of home monitors state that home cardiorespiratory monitors should not be used as a strategy to reduce the risk of SIDS; their use has not been documented to decrease the incidence of SIDS (1). Some parents or caregivers are insistent about using a home cardiorespiratory monitor, and use of these monitors may give them peace of mind. However, there is a concern that use of monitors may make parents or caregivers complacent about following safe sleep guidelines. Parents or caregivers who choose to use a home monitor should be counseled that this is not a substitute for following recommended safe sleep measures. Parents should also receive CPR training.

Exposure to tobacco smoke must be eliminated.

Infants who were not hospitalized should receive follow-up with their primary care physician within 24 hours.

Treatment reference

  1. 1. Moon RY, Carlin RF, Hand I, Task Force on Sudden Infant Death Syndrome: Evidence base for 2022 updated recommendations for a safe infant sleeping environment to reduce the risk of sleep-related infant deaths. Pediatrics 150(1):e2022057991, 2022. doi: 10.1542/peds.2022-057991

Prognosis for BRUE

Most often, BRUE is harmless and not a sign of more serious health problems or death. BRUE is unlikely to be a risk factor for sudden infant death syndrome (SIDS) (1). Most victims of SIDS do not have any types of events beforehand.

Prognosis for an event in a high-risk infant depends on the cause. For example, risk of death is higher if the cause is a serious neurologic disorder. When no cause is identified after evaluation and observation, the relationship of such events to SIDS is unclear. About 4 to 10% of infants who die of SIDS have a history of such events, and the risk of SIDS is higher if an infant has had 2 or more. Also, infants who have had an event share many of the same characteristics with infants who die of SIDS. However, incidence of BRUE, unlike that of SIDS, has not decreased in response to the Safe to Sleep® campaign.

Prognosis reference

  1. 1. McGovern MC, Smith MB: Causes of apparent life threatening events in infants: A systematic review. Arch Dis Child 89(11):1043–1048, 2004. doi: 10.1136/adc.2003.031740

Key Points

  • BRUE (brief, resolved, unexplained event) is defined as an episode of cyanosis or pallor, abnormal breathing, abnormal muscle tone, or altered responsiveness in an infant < 1 year old, with no identifiable cause, and based on the clinician’s characterization of the event and not on a caregiver’s perception that the event was life-threatening.

  • Infants who experience a BRUE can be classified as low-risk or high-risk based on history and physical examination.

  • Events in low-risk infants are unlikely to be due to a serious medical condition and require minimal assessment.

  • High-risk events have many possible causes, but often no etiology is found.

  • Respiratory, neurologic, infectious, cardiac, metabolic, and gastrointestinal disorders as well as abuse should be considered, with testing done based on clinical findings.

  • Infants with abnormal examination findings or laboratory results or who required intervention or had a worrisome history are hospitalized.

  • Treatment is directed at the cause; home monitoring may be done but has not been shown to decrease mortality.

  • Prognosis depends on cause; risk of death is increased in children with a neurologic disorder, who have had 2 or more events, who have experienced nonaccidental trauma, or who are > 6 months and have had an event of longer duration, especially if they have heart disease.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

  1. American Academy of Pediatrics: Guidelines for brief resolved unexplained events (formerly apparent life-threatening events) and evaluation of lower-risk infants (2016)

  2. Safe to Sleep®: Information for parents and caregivers about safe sleep practices for infants from the U.S. Department of Health and Human Services

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