Pulmonary diseases account for almost 50% of deaths in children younger than 1 year and about 20% of all hospitalizations of children younger than 15 years. Approximately 7% of children have a chronic respiratory disorder. Understanding the pathophysiology of many pediatric pulmonary diseases is enhanced by an appreciation of the normal growth and development of the lung.
Normal fetal lung development progresses through five stages with considerable overlap in the timing of each stage (Table 19–1). Interruption of the sequence leads to significant neonatal pulmonary difficulties that may extend lifelong. The normal human term newborn infant does not have a full complement of alveoli at birth, usually 100–150 million; this will increase with normal growth to the adult number of 300–600 alveoli. Infants who miss even the last few weeks of gestation may be challenged to meet the demands of transition from fetal life to air breathing due to incomplete alveolarization, and this may be accentuated by additional stresses such as higher altitude, suboptimal nutrition, poor air quality, or infections.
Table 19–1. Sequence of fetal lung development.
|Stage of Development ||Weeks of Gestation ||Transitions ||Pathology |
|Embryonic ||4–6 ||Mainstem bronchi form from foregut outpouching. Main PAs develop. || |
|Pseudoglandular ||6–16 ||Major bronchi form to terminal bronchioles. Conducting airways branching complete at 16 wk. ||Foregut malformations: CPAM, sequestration, bronchogenic cyst |
|Canalicular ||16–26 ||Growth extends to respiratory bronchioles. Extensive angiogenesis. ||Nonviable fetus below 22–23 wk gestation |
|Saccular ||26–36 ||Primitive air sacs and alveolar ducts form off respiratory bronchioles. Surfactant production begins. ||Respiratory distress syndrome of the newborn |
|Alveolar ||36+ ||Increased number and complexity of alveoli. ||Incomplete alveolarization |
JC: Development of the lung. Cell Tissue Res 2017;367:427–444. doi: 10.1007/s00441-016-2545-0.
PHYSICAL EXAMINATION OF THE RESPIRATORY TRACT
The complete pulmonary examination includes inspection, palpation, auscultation, and percussion. Inspection of respiratory rate and work of breathing is critical to the detection of pulmonary disease. Tachypnea, decreased sensorium, inconsolability, increased respiratory effort, retraction, poor color, and reduced movement suggest hypoxemia. Palpation of tracheal position, symmetry of chest wall movement, and vibration with vocalization can help in identifying intrathoracic abnormalities. A shift in tracheal position from midline suggests pneumothorax or significant unilateral atelectasis. Tactile fremitus may change with consolidation or air in the pleural space. Auscultation should assess the intensity and symmetry of breath sounds and the presence of abnormal sounds such as fine or coarse crackles, wheezing, or rhonchi. Wheezing or prolonged expiration suggests intrathoracic airways obstruction. Knowing the lung anatomy helps identify the location of the pathology (Figure 19–1). Percussion may identify tympanic or dull sounds that can help define an effusion or pneumothorax. Percussion is often challenging in young children.