Measurement of Pulsatile Tidal Volume, Pressure Amplitude, and Gas Flow During High-Frequency Percussive Ventilation, With and Without Partial Cuff Deflation

OBJECTIVE: With a high-frequency percussive ventilator and a mechanical lung model, to measure tidal volume (V_T), pulsatile pressure amplitude (difference between peak and nadir pulsatile pressure [ΔP]), and mean airway pressure (P̄_aw) at various pulsatile frequencies, pulsatile inspiratory-expiratory ratios (I:E_p), and pressures (measured at the interface between the pulse-generator and the endotracheal tube [P_vent]).

METHODS: With the endotracheal tube inside an artificial trachea, we manipulated the high-frequency percussive ventilation settings and adjuncts, including pulsatile frequency, I:E_p, and P_vent by manipulating pulsatile flow. We also studied the effects of partially deflating the endotracheal tube cuff. We measured P̄_aw, pulsatile pressure amplitude at the carina (ΔP_c), and pulsatile V_T at the carina. With the cuff partly deflated, we measured the fraction of inspired oxygen (F_IO2) in the gas efflux above and below the cuff.

RESULTS: Increasing the pulsatile frequency from 300 cycles/min to 600 cycles/min and changing the I:E_p from 1:3 to 1:1 significantly reduced V_T (p < 0.001). P̄_aw and ΔP_c were unaffected by the change in pulsatile frequency or I:E_p, except when we did not preserve the pulsatile flow. The measured V_T range was from 19.1 mL (at 600 cycles/min) to 47.3 mL (at 300 cycles/min). Partial cuff deflation did not significantly reduce P̄_aw or ΔP_c, but it did significantly reduce V_T and F_IO2.

CONCLUSIONS: During high-frequency percussive ventilation, the pulsatile frequency is inversely related to V_T. Partial cuff deflation reduces the delivered F_IO2.