Child's trachea, horizontal section of a healthy trachea and a congested trachea. Simplified horizontal section through the trachea of a toddler. This illustration compares the diameter of the tracheal lumen on a healthy trachea and on a congested or edematous trachea. To the left of the drawing, the tracheal lumen of a healthy trachea in a small child measures approximately 6 mm. The cartilaginous part of the trachea is shown in purple. The pink part represents the mucous membrane. We can clearly see on the right section of an edematous trachea that the tracheal lumen is very narrow, even almost non-existent. This explains why in toddlers, breathing difficulties can be significant and problematic. In the event of inflammation, the respiratory resistance is significantly increased, compared to that of an adult.