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

Abstract

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. Observational cohort animal study in the animal laboratory of a university hospital. Five foxhound dogs. 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. 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 microl/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 end-expiratory airway pressure evaporation decreased linearly over time. 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.