Friday August 7, 2009 (pediatric pearl)
Uniqueness of Pediatric Lower Airway - Part 2

(see Uniqueness of Pediatric Lower Airway - Part 1 here)

The frequency of acute respiratory failure is higher in infants and young children than in adults for several reasons. This difference can be explained by defining anatomic compartments and their developmental differences in pediatric patients that influence susceptibility to acute respiratory failure.

The intrathoracic airways and lung include the conducting airways and alveoli, the interstitia, the pleura, the lung lymphatics, and the pulmonary circulation. Noteworthy differences among pediatric children include the following:

• Infants and young children have fewer alveoli than do adults. The number dramatically increases during childhood, from approximately 20 million after birth to 300 million by 8 years of age. Therefore, infants and young children have a relatively small area for gas exchange.
• The alveolus is small. Alveolar size increases from 150-180 to 250-300 µm during childhood.
• Collateral ventilation is not fully developed; therefore, atelectasis is more common in children than in adults. During childhood, anatomic channels form to provide collateral ventilation to alveoli. These pathways are between adjacent alveoli (pores of Kohn), bronchiole and alveoli (Lambert channel), and adjacent bronchioles. This important feature allows alveoli to participate in gas exchange even in the presence of an obstructed distal airway.
• Smaller intrathoracic airways are more easily obstructed than larger ones. With age, the airways enlarge in diameter and length.
• Infants and young children have relatively little cartilaginous support of the airways. As cartilaginous support increases, dynamic compression during high expiratory flow rates is prevented.