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Acute inflammation of glottis and sub glottis.
Most common infection cause upper airway obstruction in children.
Males are affected more frequently than females.
Viral croup often presents similarly to an upper respiratory infection, with 12 to 72 hours of lowgrade fever and coryza.
Narrowing of the larynx leads to stridor, increased respiratory rate, respiratory retractions, and a barking cough. Symptoms may be exacerbated by emotional distress, are worse at night, and peak between 24 and 48 hours. Croup typically resolves spontaneously within 48 hours to one week; however, the abrupt onset and harsh cough can be concerning. Parainfluenza virus (types 1 to 3) accounts for 75% of all cases, and human parainfluenza virus 1 is the most common type. Other viral etiologies include influenza A and B, adenovirus, respiratory syncytial virus, rhinovirus, and enterovirus. Viral infection of the subglottic region and laryngeal mucosa causes inflammation and edema, which significantly decrease air movement and lead to respiratory distress and stridor. Bacterial croup is less common and may be caused by Mycoplasma pneumoniae and Corynebacterium diphtheriae.
The type of infectious agent does not affect outcomes or initial management.
The severity of croup can be assessed based on the following clinical features :
increased respiratory rate
increased heart rate
altered mental state – anxiety, agitation, confusion
work of breathing – use of accessory muscles
stridor (note that if a child’s stridor becomes softer but the work of breathing remains increased, the obstruction may actually be becoming more severe).
Hypoxia is a late sign in croup as this reflects gas exchange at the alveolar level, while the disease in croup involves the airway. Thus, measuring oxygen saturations is of no clinical benefit.
Reference : Nelson board review
Nelson text book of pediatrics