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Pediatric Pneumonia 
• Author: Nicholas John Bennett, MB, BCh, PhD; Chief Editor: Russell W Steele, MD   more...
 

Background

Pneumonia and other lower respiratory tract infections are the leading causes of death worldwide. Because pneumonia is common and is associated with significant morbidity and mortality, properly diagnosing pneumonia, correctly recognizing any complications orunderlying conditions, and appropriately treating patients are important. Although in developed countries the diagnosis is usually made on the basis of radiographic findings, the World Health Organization (WHO) has defined pneumonia solely on the basis of clinical findings obtained by visual inspection and on timing of the respiratory rate. (See Clinical Presentation.)
Pneumonia may originate inthe lung or may be a focal complication of a contiguous or systemic inflammatory process. Abnormalities of airway patency as well as alveolar ventilation and perfusion occur frequently due to various mechanisms. These derangements often significantly alter gas exchange and dependent cellular metabolism in the many tissues and organs that determine survival and contribute to quality of life.Recognition, prevention, and treatment of these problems are major factors in the care of children with pneumonia. (See Pathophysiology.)
One particular form of pneumonia present in the pediatric population, congenital pneumonia, presents within the first 24 hours after birth. To see complete information on Congenital Pneumonia, please go to the main article by clicking here.
Other respiratorytract diseases such as croup (laryngotracheobronchitis), bronchiolitis, and bronchitis are beyond the scope of this article and are not discussed further.
Next Section: Pathophysiology

Pathophysiology

An inhaled infectious organism must bypass the host's normal nonimmune and immune defense mechanisms in order to cause pneumonia. The nonimmune mechanisms include aerodynamic filtering of inhaledparticles based on size, shape, and electrostatic charges; the cough reflex; mucociliary clearance; and several secreted substances (eg, lysozymes, complement, defensins). Macrophages, neutrophils, lymphocytes, and eosinophils carry out the immune-mediated host defense.

Respiratory tract host defenses

To prevent and minimize injury and invasion by microorganisms and foreign substances,various defense mechanisms have evolved, both systemically and within the respiratory tract. Some mechanisms are nonspecific and are directed against any invasive agent, whereas others are targeted against only microbes or substances with specific antigenic determinants. Many of the defenses are compromised in the fetus and newborn infant, resulting in more frequent breaches and consequentdisruption of normal lung structure and function.[1]
Nonspecific defenses include the glottis and vocal cords, ciliary escalator, airway secretions, migratory and fixed phagocytes, nonspecific antimicrobial proteins and opsonins, and the normal relatively nonpathogenic airway flora. Anatomic structures of the upper airway and associated reflexes discourage particulate material from entering, whereascoordinated movement of the microscopic cilia on the tracheal and bronchial epithelia tends to sweep particles and mucus up the airway and away from the alveoli and distal respiratory structures.
Mucoid airway secretions provide a physical barrier that minimizes epithelial adhesion and subsequent invasion by microorganisms. These secretions typically contain complement components, fibronectin, andother proteins that bind to microbes and render them more susceptible to ingestion by phagocytes. Alveolar and distal airway secretions also include whole surfactant, which facilitates opsonization and phagocytosis of pathogens, as well as surfactant-associated proteins A (Sp-A) and D (Sp-D), both of which modulate phagocytosis, phagocyte production of oxyradicals, and cytokine elaboration.
The...