Optimization of high-frequency oscillatory ventilation for the treatment of experimental pneumothorax.

OBJECTIVE: To determine the effect of frequency, amplitude, inspiratory time, and mean airway pressure on gas flow through a chest tube in an animal model of pneumothorax treated with high-frequency oscillatory ventilation (HFOV).

DESIGN: Observational study.

SETTING: Animal laboratory.

SUBJECTS: Neonatal piglets (n = 12).

INTERVENTIONS: After saline lavage, a model of experimental pneumothorax was created by selective right mainstem intubation and manual ventilation at high-peak inspiratory pressure. A chest tube was placed, and gas flow through the chest tube was measured with a pneumotachometer during HFOV with the SensorMedics 3100A. The effects of frequency, inspiratory time, amplitude, and mean airway pressure on chest tube gas flow were determined.

MEASUREMENTS AND MAIN RESULTS: Gas flow through the chest tube was significantly higher (p <.001) at 5 Hz (601 +/- 23 mL/min) than at 10 Hz (464 +/- 64 mL/min) or 15 Hz (400 +/- 11 mL/min), while mean airway pressure, inspiratory time, and PaCO2 were kept constant. Gas flow was higher at an inspiratory time of 50% compared with one of 30% (645 +/- 49 vs. 436 +/- 36 mL/min, respectively). Gas flow was directly related to amplitude (284 mL/min at an amplitude of 10 cm H2O, increasing to 877 mL/min at an amplitude of 80 cm H2O) when a 3.5-mm endotracheal tube was used; however, gas flow was attenuated at amplitudes of >40 cm H2O when smaller endotracheal tubes were used. Gas flow increased significantly with the increase of mean airway pressure from 92 mL/min at 15 cm H2O to 1433 mL/min at 30 cm H2O.

CONCLUSIONS: In a neonatal piglet model of pneumothorax treated with HFOV, with amplitude adjusted to maintain constant alveolar ventilation, gas flow through the chest tube was significantly lower at 15 Hz compared with either 10 Hz or 5 Hz. Chest tube gas flow increased with increasing inspiratory time, amplitude, and mean airway pressure. These findings support the use of higher frequencies, short inspiratory times, low amplitudes, and low mean airway pressures for healing air leak with HFOV.