The Pediatric Airway
The most important feature of conducting safe pediatric sedation is the ability to assess and manage the pediatric airway. The upper airway is composed of three segments:
- Supraglottic – the most poorly supported segment, consisting primarily of the pharynx;
- Glottic (larynx) –comprising the vocal cords, subglottic area, and cervical trachea; and
- Intrathoracic – consisting of the thoracic trachea and bronchi.
There are a number of developmental characteristics that distinguish the pediatric airway from the adult airway:
- The pediatric airway is smaller in diameter and shorter in length than the adult’s.
- The young child's tongue is relatively larger in the oropharynx than the adult’s.
- The larynx in infants and young children is located more anteriorly compared with the adult’s.
- The epiglottis in infants and young children is relatively long, floppy, and narrow.
- In children younger than 10 years of age, the narrowest portion of the airway is below the glottis at the level of the cricoid cartilage.
Consequently, the small caliber of the pediatric upper airway, the relatively larger tongue, and the “floppy” and relatively long epiglottis predispose young children to airway obstruction during sedation. In addition, the large occiput of the infant places the head and neck in the flexed position when the patient is placed recumbent, further exacerbating airway obstruction.
During normal inspiration, negative intrapleural pressure generated in the thorax creates a pressure gradient from the mouth to the airways, resulting in airflow into the lungs. Extrathoracic airway caliber decreases during inhalation, whereas intrathoracic airway diameter tends to increase. Under normal conditions, changes in airway caliber during respiration are clinically insignificant. However, significant narrowing of the upper airway increases airway resistance, and a higher pressure gradient across the airway is required if minute ventilation is to be maintained. A greater pressure gradient generated across the airway accentuates the normal inspiratory and expiratory effects on the airway. Consequently, the greater negative pressure generated in the pharynx during inspiration tends to further collapse the upper airway.
Resistance across the airway under laminar flow conditions is directly related to the length of the tube and the viscosity of the gas and indirectly related to the fourth power of the radius. Thus, airway resistance is primarily influenced by the diameter of the airway. In addition, the relationship between the pressure gradient across the airway and the subsequent flow rate generated is influenced greatly by the nature of the flow (laminar versus turbulent). Laminar flow is inaudible and streamlined, typically through straight, unbranching tubes. The flow rate under laminar flow conditions is directly related to the pressure gradient (driving pressure). Conversely, turbulent flow is audible and disorganized, through branched or irregular tubes. Turbulent flow (e.g., stridor) tends to occur with high flow rates and often under conditions of airway narrowing and high resistance. A greater pressure gradient is required to move air through a tube under turbulent flow conditions.