Chest
Volume 110, Issue 2, August 1996, Pages 494-497
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Laboratory and Animal Investigations
Pressures Required to Move Gas Through the Native Airway in the Presence of a Fenestrated vs a Nonfenestrated Tracheostomy Tube

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Subject

It is occasionally desirable for patients with a tracheostomy tube to breathe through their native airway. We hypothesized that capped tracheostomy tubes with cuffs deflated would create substantial additional resistance to airflow without fenestration but would provide minimal resistance to airflow when the tube had a fenestration.

Methods

Two tracheal models were tested simulating a large (26 mm) and an average (18 mm) trachea. Tests were carried out with fenestrated and nonfenestrated tracheostomy tubes of sizes ranging from No. 4 to No. 10. Negative pressure inspiration was simulated using suction.

Results

With a large trachea or small tubes, the suction required to generate flows of 40 L/min or greater remained less than 5 cm H2O with or without a fenestration. However, with an average-sized trachea and no fenestration, the pressure required to generate flows of 40 L/min or greater exceeded 5 cm H2O and with No. 8 or No. 10 tubes exceeded 20 cm H2O. A fenestration routinely reduced the required pressure to less than 5 cm H2O.

Conclusion

The effort required to move gas across the native airway in the absence of a fenestration may be substantial. If a patient is to breathe through a native airway, a fenestrated tube should be used unless the tracheostomy tube is a No. 4.

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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