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Pediatric Airway - Cross sectional area

last modified on: Fri, 05/10/2019 - 07:43

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  1. Minimal reduction of the cross sectional area of a pediatric airway may have significant consequences, resulting in dyspnea.
    1. The cross sectional area may be calculated using the formula:  pi (3.14) * r ^2
      1. The average diameter of the cricoid cartilage in an infant is approximately 6 mm.  This means that the cross sectional area may be calculated as:  3.14*9 = 28 mm^2.
      2. Reduction of the pediatric airway by 1 mm results in a reduced radius from 3 mm to 2 mm.  This would result in a new cross sectional area of 3.14*4 = 12.5 mm ^ 2.
        1. This is a reduction in airway size of more than 50%.
  2. Average sizes for children by age are as follows:

            Ages       0-1 - 6 mm
                          1-2 - 7.5 mm
                          2-4 - 8 mm
                          4-5 - 9 mm

  1. Althought we have given consideration to the change in cross sectional area, the main concern with the decreased size of the pediatric airway is the correlating decrease in airflow.  As the diameter of the tube is halved, the flow through this tube is reduced to 1/16 of the original flow.
    1. Flow is directly proportional to D^4.
  2. Another consideration when thinking of flow of air through a cylinder is viscosity.  As viscosity decreases, the flow increases.  This is why the use of Heliox may be advantageous.