Partial liquid ventilation: effects of liquid volume and ventilatory settings on perfluorocarbon evaporation

During partial liquid ventilation perfluorocarbons are eliminated mainly by evaporation via the airways. The effects of intrapulmonary perfluorocarbon volume, respiratory rate, tidal volume, as well as the level of end-expiratory pressure on perfluorocarbon elimination from isolated lungs, were studied. Nonperfused rabbit lungs underwent partial liquid ventilation (2-15 mL x kg(-1) perfluorocarbon) with variable levels of end-expiratory pressure (0-10 cmH2O), respiratory rates (15-60 breaths x min(-1)) and tidal volumes (3.3-10.0 mL x kg(-1)). Evaporative loss of perfluorocarbon was determined gravimetrically as rate of change in lung weight. At constant respiratory settings, intrapulmonary liquid volume determined evaporative loss in a nonlinear fashion. Mean evaporation at a liquid volume of 5 mL x kg(-1) was 13% lower compared to evaporation at a liquid volume of 15 mL x kg(-1). Any increase in end-expiratory pressure reduced perfluorocarbon evaporation, e.g. by approximately 50% when end-expiratory pressure was increased from 0 to 10 cmH2O. At constant end-expiratory pressure and perfluorocarbon filling evaporation increased in a linear fashion with increasing respiratory rate and tidal volume. In summary, the experiments suggested that evaporative loss of perfluorocarbons during partial liquid ventilation of isolated lungs is increased with increasing intrapulmonary liquid volume, respiratory rate and tidal volume and is reduced in a level-dependent fashion by the application of positive end-expiratory pressure.