A brief resolved unexplained event (BRUE) is a sudden, transient episode of altered breathing, colour, tone or responsiveness in an infant under 1-year-old, which resolves spontaneously and has no clear explanation after clinical assessment. BRUE is not a diagnosis but rather a clinical presentation, requiring careful evaluation to determine underlying causes. The term BRUE replaces the older term apparent life-threatening event (ALTE), refining the definition and introducing a risk-stratification approach..
Definition of BRUE
The American Academy of Pediatrics (AAP) 2016 Criteria defines BRUE as a sudden, brief, and unexplained event in an infant under 1 year old that has completely resolved and meets all of the following criteria:
1. Occurs in an infant <12 months old
2. Brief duration (<1 minute, typically 2–30 seconds)
3. Resolves spontaneously with a return to baseline
4. No identifiable medical cause after thorough history and examination
5. At least one of the following features is present:
- Cyanosis or pallor
- Absent, decreased, or irregular breathing
- Marked change in muscle tone (hypotonia or hypertonia)
- Altered level of responsiveness
Key point: A BRUE should only be diagnosed when a complete clinical evaluation fails to identify a specific cause for the event.
Risk factors for BRUE
Certain factors increase the likelihood of BRUE episodes:
- Prematurity (<32 weeks gestation)
- Age <10 weeks
- Recent anesthesia exposure
- Airway abnormalities (e.g., laryngomalacia)
- Gastroesophageal reflux disease (GERD)
- Previous apneic episodes
- Respiratory syncytial virus (RSV) infection
- Feeding difficulties
Differentiating low-risk vs. high-risk BRUE
The AAP stratifies BRUE into low-risk and high-risk groups based on recurrence risk and association with serious conditions.
A low-risk BRUE is identified if all of the following apply:
- Age >60 days.
- Gestational age ≥32 weeks and postconceptional age ≥45 weeks.
- Event duration <1 minute.
- First BRUE episode (not recurrent).
- No CPR was required by a trained healthcare provider.
- No concerning historical features or physical exam findings.
A high-risk BRUE is identified if any of the following apply:
- Age <60 days.
- Gestational age <32 weeks.
- Event duration >1 minute.
- Recurrent episodes.
- CPR required.
- Concerning history or abnormal physical exam.
Differential diagnosis
BRUE is a diagnosis of exclusion. Other serious conditions must be ruled out:
|
Category |
Potential causes
|
|
Respiratory |
Pertussis, bronchiolitis, aspiration, airway obstruction
|
|
Cardiac |
Arrhythmias (e.g. long QT syndrome, SVT), congenital heart disease
|
|
Gastrointestinal |
Gastroesophageal reflux disease (GORD), milk protein allergy
|
|
Neurological
|
Seizures, breath-holding spells, intracranial haemorrhage
|
|
Metabolic
|
Hypoglycaemia, inborn errors of metabolism
|
|
Infectious
|
Sepsis, meningitis, RSV, UTI
|
|
Non-accidental injury (NAI)
|
Child abuse, suffocation, poisoning |
Clinical assessment
History:
- Event details: Duration, colour change, breathing pattern, tone, seizure-like movements.
- Preceding events: Fever, vomiting, feeding issues, infections.
- Post-event behaviour: Normal vs. lethargic, irritable.
- Positioning: Prone/supine, risk of airway obstruction.
- Family history: Sudden infant death syndrome (SIDS), arrhythmias, metabolic disorders.
- Social history: Co-sleeping, smoking, substance exposure.
Examination:
- Vital signs: Temperature, HR, RR, BP, oxygen saturation.
- General appearance: Alert vs. lethargic.
- Respiratory: Stridor, nasal flaring, chest retractions.
- Cardiac: Murmurs, femoral pulses (coarctation of the aorta).
- Neurological: Hypotonia, hypertonia, abnormal reflexes.
- Skin exam: Bruising, signs of non-accidental trauma.
Investigations in BRUE
Low-risk BRUE:
- No investigations are required in most cases.
- Some units may perform:
- Capillary blood gas (CBG): Assess blood glucose, bicarbonate, and lactate for metabolic abnormalities.
- ECG: Evaluate for arrhythmias, particularly prolonged QT interval.
- There is no need for prolonged observation or monitoring.
High-risk BRUE:
- Minimum required investigations:
- CBG: Assess blood glucose, bicarbonate, and lactate to screen for metabolic disease.
- ECG: Evaluate for arrhythmias (QT interval assessment).
- Continuous cardiorespiratory monitoring during observation.
- Additional investigations (guided by local protocols and clinical suspicion):
- Blood tests: Full blood count, U&Es, CRP.
- Nasopharyngeal aspirate (NPA): Assess for pertussis and/or RSV if infection suspected.
Management
Low-risk BRUE:
- Brief period of monitoring in ED (1–4 hours) with pulse oximetry.
- Provide parental education and CPR training.
- Discharge with reassurance.
- Organise follow-up within 24 hours.
High-risk BRUE:
- Admit for continuous monitoring and targeted investigations.
- Investigate underlying causes based on suspected aetiology (e.g. infection, cardiac, metabolic or neurological causes).
- Consider blood tests, ECG, brain imaging and polysomnography if clinically indicated.
- Speciality referral (neurology, cardiology, respiratory) if required.
Parental counselling:
- Educate on safe sleep practices (supine sleeping, no soft bedding).
- Reassure that low-risk BRUE is unlikely to recur.
- Provide clear guidance on when to seek medical attention.
Thank you to the joint editorial team of MRCEM Exam Prep for this article.
