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

Objective: Perfluorocarbons 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 cmH(2)O 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 cmH(2)O was 19.6+/-3.8 mul/kg per minute; this decreased by 28% at an end-expiratory airway pressure of 0 cmH(2)O and increased by 46% at an end-expiratory airway pressure of 10 cmH(2)O. At equal levels of endexpiratory 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.