Positive end-expiratory pressure during partial liquid ventilation: Impact on lung volume recruitment and gas exchange

Positive end-expiratory pressure (PEEP) is used during conventional ventilation (CV) to recruit lung volume, improve V/Q matching, and improve gas exchange. Partial liquid ventilation (PLV) using FRC amounts of perfluorocarbon recruits lung volume mechanically, and may alter the subsequent effect of applied PEEP. In 9 newborn piglets with saline lavage-induced lung injury (PaO2<60 torr at FiO2 1.0), we tested the hypothesis that PEEP applied during PLV would not affect gas exchange, compliance, FRC or hemodynamics. PLV animals received intratracheal perflubron (LiquiVent™); after 1 hour stabilization, PEEP was increased, then decreased at constant tidal volume in a stepwise fashion from 4 cmH20 - 8 - 12 - 8 - 4. After 30 minutes at each PEEP level, blood gases, blood pressures, heart rates, lung mechanics (VenTrak) and ΔFRC (mL/kg; respiratory inductive plethysmography) were measured. Data analysis used paired/unpaired t-tests with Bonferroni correction. Means ±SD are shown. PEEP level (cmH20) 4a 8 12 8 4b pH 7.43±0.03 7.48±0.04* 7.52±0.03*† 7.44±0.02* 7.39±0.02*† a/A 0.35±0.05 0.44±0.04* 0.59±0.04*† 0.34±0.06* 0.19±0.03*†+ Cdyn 0.8±0.03 0.9±0.03 0.8±0.03 1.1±0.1* 1.0±0.1*†+ BP 57±5 57±6 57±7 57±6 58±6 ΔFRC - +4.0±0.8* +7.0±1.0* -7.0±1.0* -5.0±1.0 * p<0.05 vs previous; † p<0.05 vs 4a,4b; + p<0.05 vs 4a Conclusions: In an animal model of respiratory distress, increasing PEEP during PLV over the range studied improved gas exchange without hemodynamic compromise in a similar fashion to PEEP during CV, by recruiting lung volume. As PEEP was reduced, a/A fell disproportionately to FRC, possibly due to redistribution of perflubron.