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 [DeltaP];), and mean airway pressure (P (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 P (aw), pulsatile pressure amplitude at the carina (DeltaP(c)), and pulsatile V(T) at the carina. With the cuff partly deflated, we measured the fraction of inspired oxygen (F(IO(2))) 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). P (aw) and DeltaP(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 P (aw) or DeltaP(c), but it did significantly reduce V(T) and F(IO(2)). CONCLUSION During high-frequency percussive ventilation, the pulsatile frequency is inversely related to V(T). Partial cuff deflation reduces the delivered F(IO(2)).