The effective tracheal diameter that causes air trapping during jet ventilation

Area of Science:

• Mechanical Ventilation
• Respiratory Physiology

Background:

• Jet ventilation involves high-flow gas injection via a small tracheal catheter.
• Air trapping, an increase in end-expiratory lung volume, can occur if the trachea is too narrow for exhalation.

Purpose of the Study:

• To determine the critical effective tracheal diameter at which air trapping begins during jet ventilation.
• To develop a predictive equation for tidal volume in jet ventilation.

Main Methods:

• Utilized a mechanical lung model to simulate jet ventilation.
• Measured exhalation time across various parameters including gas flow rate, injection time, lung compliance, upper airway resistance, and effective tracheal diameter.

Main Results:

• Derived a multivariable equation relating tidal volume to ventilation parameters and tracheal diameter.
• Identified a critical effective tracheal diameter of 4.0 to 4.5 mm, below which expiratory time significantly increases.
• Air trapping occurs with a tracheal diameter < 4.5 mm, especially at respiratory rates > 12 breaths/min.

Conclusions:

• Effective tracheal diameter is a crucial factor in preventing air trapping during jet ventilation.
• Maintaining an effective tracheal diameter of at least 4.5 mm is essential for safe jet ventilation.
• Factors promoting gas entry into the lungs exacerbate the risk of air trapping if tracheal diameter is insufficient.