The differential diagnosis is extensive, and although a broad workup is often started in the ED including evaluation for sepsis, occult infection, and metabolic disorders, a cause is infrequently found
Idiopathic (~50%)
GERD
Seizure
Respiratory tract infection (e.g. bronchiolitis)
Misinterpretation of benign process (e.g. periodic breathing)
Vomiting/choking episode
Pertussis
Nonaccidental trauma
Poisoning
Serious bacterial infection (e.g.meningitis,  pneumonia, Bacteremia, UTI))
Must consider in all febrile patients with BRUE
Electrolyte abnormalities (including hypoglycemia and other glucose abnormalities)
Must consider in all febrile patients with BRUE
Arrhythmia
Anemia
Breath-holding spell (6mo - 4yrs)
Metabolic disease
Brief resolved unexplained event
The differential diagnosis is extensive, and although a broad workup is often started in the ED including evaluation for sepsis, occult infection, and metabolic disorders, a cause is infrequently found[2]
Deterioration after intubation
Idiopathic 
Headache during pregnancy
GERD
Acute chest pain
Seizure