EFFECT OF THE TI TE RATIO ON MEAN INTRATRACHEAL PRESSURE IN HIGH-FREQUENCY OSCILLATORY VENTILATION/

In high-frequency oscillatory ventilation (HFOV), an adequate mean air way pressure is crucial for successful ventilation and optimal gas exc hange, but air trapping cannot be detected by the usual measurement at the y piece. Intratracheal pressures produced by the high-frequency o scillators HFV-Infantstar (IS), Babylog 8000 (BL), and the SensorMedic s 3100A ISM) [the latter with either 30% (SM30) or 50%(SM50) inspirato ry time] were investigated in four anesthetized tracheotomized female piglets that were 1 day old and weighed 1.6-1.9 kg (mean 1.76 kg). The endotracheal tube was repeatedly clamped while the piglets were venti lated with an oscillation frequency of 10 Hz, and the airway pressure distal of the clamp was recorded as a measure of average intrapulmonar y pressure during oscillation. Clamping resulted in a significant decr ease of mean airway pressure when the piglets were ventilated with SM3 0 (-0.86 cmH(2)O), BL (-0.66 cmH(2)O), and IS (-0.71 cmH(2)O), but air way pressure increased by a mean of 0.76 cmH(2)O with SM50. Intratrach eal pressure, when measured by a catheter pressure transducer at vario us oscillation frequencies, was lower than at the y piece by 0.4-0.9 c mH(2)O (SM30), 0.3-3 cmH(2)O (BL), and 1-4.7 cmH(2)O (IS) but was 0.4- 0.7 cmH(2)O higher with SM50. We conclude that the inspiratory-to-expi ratory time(TI/TE) ratio influences the intratracheal and intrapulmona ry pressures in HFOV and may sustain a mean pressure gradient between the y piece and the trachea. A TI/TE ratio < 1:1 may be useful to avoi d air trapping when HFOV is used.