Partial liquid ventilation: Effects of positive end-expiratory pressure on perfluorocarbon evaporation from the lungs of anesthetized dogs

Objective: bons are eliminated during partial liquid ventilation mainly by evaporation via the airways. We examined whether this is affected by the level of end-expiratory airway pressure. Design and setting: Observational cohort animal study in the animal laboratory of a university hospital. Subjects: Five foxhound dogs. Interventions: The anesthetized dogs underwent partial liquid ventilation (5 ml/kg perfluorocarbon) at constant respiratory rate (17±1 breaths/min) and tidal volume (10 ml/kg). The level of end-expiratory airway pressure was varied repeatedly between 0, 5, and 10 cmH₂O every 25 min. Measurements and results: Expired gas was collected in reservoirs to determine evaporative perfluorocarbon loss gravimetrically. Any increase in end-expiratory airway pressure increased while any decrease in end-expiratory airway pressure reduced evaporative perfluorocarbon loss. Mean initial elimination at an end-expiratory airway pressure of 5 cmH₂O was 19.6±3.8 μl/kg per minute; this decreased by 28% at an end-expiratory airway pressure of 0 cmH₂O and increased by 46% at an end-expiratory airway pressure of 10 cmH₂O. At equal levels of end-expiratory airway pressure evaporation decreased linearly over time. Conclusions: Our results suggest that the level of end-expiratory airway pressure is a determinant of evaporative perfluorocarbon loss and may have relevance for maintenance dosing and instillation intervals during partial liquid ventilation.