The subglottis is typically involved in infants and children presenting with classic croup. The subglottis is defined as the segment of the upper airway directly below the vocal cords fusing with the upper trachea. It contains pseudostratified columnar respiratory epithelium, which is loosely adherent and prone to swelling. Because this area is fully cartilagenized in childhood, it lacks the ability to expand and thus can produce early symptoms due to even small degrees of inflammation.

Stridor is the high-pitched adventitious sound produced in the respiratory cycle by the turbulent flow of respiratory gases through a segmental narrowing in the airway. It can be biphasic, inspiratory, or expiratory, depending on the anatomic location.

Inspiratory stridor is characteristic of laryngeal or supraglottic obstruction. Such conditions as laryngeal papillomatosis, laryngeal web, laryngomalacia, and vocal cord paresis produce inspiratory stridor. Expiratory stridor is usually typical of intrathoracic processes such as extrinsic tracheal compression by a vascular ring or mass, tracheomalacia, or bronchotracheitis. Biphasic stridor is indicative of lesions or infections involving both the larynx and subglottis such as the croup syndrome, subglottic stenosis, or intralaryngeal masses.

Croup is a generalized term referring to infections of the upper respiratory tract with a characteristic cough, inspiratory stridor, and possible respiratory distress. Other terms, namely, laryngotracheobronchitis, spasmodic croup, and bacterial tracheitis, are interwoven within the croup syndrome but have specialized meanings. For instance, spasmodic croup suggests a noninfectious inflammatory process as opposed to the viral etiology of laryngotracheobronchitis. Most cases occur during the colder months. There is a 1:1 male-to-female prevalence. Also known as laryngotracheobronchitis because of the structures involved, croup is caused by a number of viruses, including human rhinovirus; Haemophilus parainfluenzae virus type 1, 2, and 3; respiratory syncytial virus; influenza virus; or human corona virus. It commonly affects children between 6 months and 3 years of age, with a median age of 18 months. It manifests subacutely as an exacerbation of cold symptoms with low fever, barking cough, noisy breathing, and hoarseness. Exudative inflammation of the upper airway may cause
dyspnea and in extreme cases can lead to exhaustion and frank hypoxia. In most cases, it is self-limited and benign.

A full differential for this condition involves a host of infectious causes. Among the most important are bacterial tracheitis, diphtheria, retropharyngeal abscess, peritonsillar abscess, measles, and Epstein-Barr viral infection. Other causes to be considered are thermal burns, foreign body aspiration, laryngeal fractures, angioneurotic edema, vocal cord paralysis, and uvulitis.

This is a severe and potentially fatal disease of an infectious nature occurring as a consequence of infection with Staphylococcus aureus, various streptococcal species, and Haemophilus influenzae. It occurs in colder weather in young children as a secondary complication of viral laryngotracheitis. Although presenting the same symptoms as epiglottitis, it tends not to evolve as rapidly and generally does not have odynophagia and drooling, two characteristic signs of epiglottitis. Most of these children require intubation for thick and difficult-to-clear secretions, and during endoscopy, subglottic edema with mucosal ulceration is seen.

A host of anatomic problems can share similar signs and symptoms with the infectious agents causing airway compromise. It is only by the absence of fever and the chronicity of the situation that these are distinguishable. Vocal cord paralysis, laryngeal webs, laryngomalacia, subglottic masses (hemangiomas), and stenosis as well as vascular anomalies are to be included.

One evaluates the following parameters in assessing severity of the illness: (1) Work of breathing: Is there tachypnea and/or retractions? (2) Chest wall motion: Is the tidal volume adequate with inspiration? (3) Overall appearance: Is the child cyanotic, obtunded, or comfortable? (4) Vocal quality: Is there stridor, diminished voice, or cry? Severe croup unresponsive to the medical therapy may require tracheal intubation. Once the diagnosis of croup has been established, the child is given a croup score, which helps determine therapy (Table 41.1).

Mild croup is treated with inspired gas humidification, hydration, and oxygen to improve the attendant hypoxemia. Croup tents, croupettes, and blow-by oxygen are helpful. Steroids and racemic epinephrine are the prime modalities of therapy. If the patient has moderate retractions and appears dyspneic, 0.5 mL of a 2.25% racemic epinephrine solution in 2.5 mL of normal saline can be administered via nebulizer.

Airway resistance can be high with the reactive transudation and intraluminal narrowing. By vasoconstricting the arterioles of the mucosal vasculature, racemic epinephrine relieves edema. Racemic epinephrine is a 1:1 mixture of the levo (L) and dextro (D) isomers to limit cardiac stimulation because only the L form is an active component. Patients improve markedly within 30 minutes, but the clinician should be cautioned that the relief may only last a few hours, although patients tend not to be in worse condition when it wears off. The Beta 2 activity will cause bronchial smooth muscle relaxation. Avoid racemic epinephrine in children with glaucoma and ventricular outflow obstruction.