Croup in Children

Pathophysiology of croup

The development of croup syndrome is due to the anatomical and physiological characteristics of the respiratory system in young infants. They have a small airway diameter, a soft and pliable cartilaginous framework, and a funnel-shaped larynx. In addition, the mucosa and submucosa are rich in lymphoid tissue and blood vessels, but have poorly developed elastic fibers. An additional factor is the tendency of the muscles that narrow the glottis toward hyperexcitability.

The etiology is mainly based on viruses (parainfluenza, adenovirus, RSV). Under the influence of infection, two main mechanisms of obstruction develop:

1. Inflammatory edema and infiltration of tissues.
2. Obtrusion of the lumen by thick mucus due to glandular hypersecretion.

The inflammation is localized in the subglottic region. Because the mucosa is tightly fused to the tissues in the area of the vocal cords, the edema cannot spread upward. The process proceeds exclusively in a descending path toward the trachea, causing a rapid narrowing of the lumen.

Clinical presentation and symptom triad

The onset of the attack is typically preceded by a prodromal period lasting 1–3 days with fever and catarrhal symptoms of ARVI. The attack itself begins suddenly, usually in the evening or at night.

Local manifestations form the classic croup triad:

• Dysphonia — change in voice (hoarseness) due to incomplete closure of the inflamed vocal cords.
• Specific cough — dry, short, hacking, the so-called "barking" cough.
• Stridor (stridor) — noisy stenotic breathing, usually with difficult inspiration (inspiratory dyspnea) and the involvement of accessory muscles.

In addition to local signs, systemic disorders occur due to progressive hypoxemia: skin pallor, perioral cyanosis, and neurological changes ranging from severe agitation to lethargy.

Classification of laryngeal stenosis by severity

Patient assessment is based on analyzing the work of breathing, pulse, skin color, and level of consciousness. There are 4 degrees of severity:

• Grade 1 (Compensated): Symptoms (stridor, dyspnea) appear only upon agitation or exertion. At rest, breathing is even, saturation is normal. Lasts from several hours to 1–2 days.
• Grade 2 (Subcompensated): Dyspnea and the involvement of accessory muscles are visible at complete rest. The child is agitated, tachycardia and cyanosis of the nasolabial triangle are pronounced. Saturation drops below 95%.
• Grade 3 (Decompensated): Exhaustion of compensation. Voice impaired up to complete aphonia, cough becomes quiet and shallow. Breathing becomes mixed, paradoxical pulse appears (drop in wave during inspiration). Agitation is replaced by CNS depression. Saturation below 92%.
• Grade 4 (Asphyxia): Terminal stage. Deep coma, total body cyanosis. Breathing is arrhythmic with episodes of apnea, heart sounds are muffled. Bradycardia develops, leading to asystole.

Diagnostics and potential complications

The diagnosis is established based on the clinical picture. The basic algorithm includes history taking (vaccination status must be clarified to rule out diphtheria), physical examination, auscultation, and pulse oximetry. If necessary, blood gas analysis, fiberoptic laryngoscopy, and bacteriological swabs (e.g., for Klebsiella diphtheriae) are prescribed.

Viral croup rarely leads to irreversible consequences on its own if care is provided on time. The main threat is the addition of secondary bacterial microflora. This provokes severe complications such as bacterial tracheitis, purulent laryngotracheobronchitis, and pneumonia. Pneumonia is the leading cause of death in this pathology.

What else to study on this topic

• Differential diagnosis of croup and foreign body aspiration
• Features of acute stenosis in diphtheria (true croup)
• Pathogenesis of acid-base balance disorders during decompensation
• Principles of bacteriological diagnosis and taking a swab for Klebsiella diphtheriae
• Prehospital emergency care algorithm for urgent obstruction

Other topics in "Chapter 13. Main syndromes requiring emergency care"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.