Animal and Lung Model Studies of Double-Lumen Tracheal Tubes for High Frequency Ventilation

The application of double-lumen tracheal tubes for high frequency ventilation (HFV) was evaluated in anesthetized dogs and in a lung model. Tracheal tubes with different inspiratory lumen:expiratory lumen size ratios (1:10, 1:4, 1:1) were used. During HFV the smaller lumen was used as the inspiratory port and the larger as the expiratory port. A fluidic ventilator was used with an inspiratory:expiratory time ratio of 0.3 and driving pressures of 5, 10, and 20 psi. Insufficient (restricted) expiration occurred with the IL:EL 1:4 and 1:1 tubes and f≥200/min. Under these conditions, gas trapping elevated mean airway pressures (Paw). The IL:EL 1:10 tracheal tube has previously been shown to provide HFV without entrainment of a second gas. In the present study the 9-mm external diameter 1:10 tube provided adequate alveolar ventilation (normal Paco2) at low Paw with f 100-200/min and driving-gas pressures of 10 and 20 psi. In addition, the large expiratory lumen afforded low expiratory flow resistance; there was no gas trapping. Adequate oxygenation (Pa02) was maintained with all tracheal tubes at driving pressures of 10 and 20 psi and f 300/min or less. Subsequently, using the same ventilator settings and average tidal volumes as in the animal experiments, we measured inspiratory gas velocities by a linear pneumotachograph in a lung model. We concluded that the increase of dead space ventilation and shortening of expiratory time with f >100/min provided less efficient ventilation. Thus, with HFV via the IL:EL 1:10 double-lumen tube, a ventilatory rate of 100/min gave the most efficient ventilation and oxygenation, as determined by Paco2 and Pa02. The functional and dimensional characteristics of the IL:EL 1:10 tube also make it a suitable part of a low-compression patient circuit for volume-controlled HFV.