Partial liquid ventilation (PLV) may be performed using high frequency techniques (Peds Res 1996; 39:350A). In this study, we investigate the impact of changes in ventilator frequency (Hertz, Hz) during PLV with high frequency oscillation (HFO; SensorMedics 3100A) on gas exchange in ten newborn (1.2-3.8 kg) saline-lavaged injured piglets (PaO2<60 torr, FiO2 1.0). During volume-targeted conventional ventilation (CV, Vt=12-15 ml/kg; Dräger Babylog), we instilled perflubron (LiquiVent®) to FRC and normalized blood gases using continuous in-line monitoring (Paratrend 7®). Piglets were randomized to HFO (FiO2=1.0, Ti = 0.33) with the following frequency sequences: 5-10-15-10-5 Hz (n=3); 10-15-5-15-10 Hz (n=2); 15-10-5-10-15 Hz(n=3); 10-5-15-5-10 Hz (n=2). Animals were treated at each Hz level for 30 minutes; amplitude was adjusted to maintain PaCO2 40-60 torr. After 15 minutes Paw was adjusted to maintain PaO2 80-120 torr. Animals were rotated every 30 minutes; perflubron losses were replaced hourly. Arterial blood gases were recorded and oxygenation index (OI) calculated at 30 minutes. Data from the different Hz treatment periods and CV were combined and compared using ANOVA, then Duncan's Multiple Range Test. Table

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HFO at 5 Hz provided gas exchange with the least amount of Paw compared to 10 and 15 Hz. Oxygenation was greatest during CV despite using higher Paw during HFO at any Hz.(LiquiVent® and funding for this study rovided by Alliance Pharmaceutical Corp. and Hoechst Marion Roussel. 3100A provided by SensorMedics Critical Care. Paratrend 7(r) provided by Diametrics Medical, Inc. Additional funding provided by NPHA).