Chest
Laboratory and Animal InvestigationsPressures Required to Move Gas Through the Native Airway in the Presence of a Fenestrated vs a Nonfenestrated Tracheostomy Tube
Section snippets
MATERIALS AND METHODS
The pressure drop across the model upper airway was determined using a standard tracheostomy tube and a fenestrated tracheostomy tube (Shiley; Irvine, Calif). The tracheostomy tubes were placed into one of two 15-cm-long model tracheas of flexible plastic with diameters of 18 mm (average-sized trachea) and 26 mm (large-diameter trachea), with tracheostomy holes 5 cm from the end (Fig 1). Putty was used to seal the junction of the tube with the tracheal model. Suction was used to simulate a
RESULTS
The pressures necessary to generate the test flows are demonstrated in Figure 2. Using the 18-mm tracheal model, the nonfenestrated No. 6 tube required nearly 10 cm H2O even at the relatively modest flow of 40 L/min, and 18.4 cm H2O at a 60 L/min flow. The No. 10 tube required greater than 20 cm H2O at all flows, and the No. 8 tube required more than 20 cm H2O at all flows higher than 20 L/min. Fenestration reduced the pressure required at 20 L/min flows to less than 1 cm H2O for all tube sizes
DISCUSSION
While numerous articles exist on the resistance to flow offered by tracheostomy tubes, almost no literature concerns itself with the resistance to breathing through the native airway while a tracheostomy tube is in place. The pressure drop across the normal native human airway ranges from less than 1 cm H2O at flows of 20 L/min to 5 cm H2O at flows of 100 L/min.2 The current study demonstrates that in an average-sized trachea, all sizes greater than a No. 4 tube require efforts far in excess of
ACKNOWLEDGMENT
The authors thank Richard Goodman, MD, for his assistance with this article.
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