Assessment of the development of choked flow during total liquid ventilation

ObjectiveThe flow rate of a liquid drainage from the lungs is limited because of the elastic nature of the airways. This study was designed to clarify the relationship between intrapulmonary liquid volume and the development of the flow limitation or choked flow phenomenon as a function of expiratory flow rate during total liquid ventilation with perflubron. DesignProspective animal study. SettingUniversity research laboratory. SubjectsRabbits with a weight of 3.2 ± 0.3 kg. InterventionsAfter the rabbits were killed, the lungs were filled to functional residual capacity with perflubron, followed by administration of an additional volume of 30, 45, or 60 mL of perflubron (initial volume = functional residual capacity + additional volume). Measurements and ResultsIn one set of five animals, the intratracheal pressure at the occurrence of choked flow was established at −20 mm Hg. In another set of six animals, we demonstrated that the volume remaining in the lung at the point of development of choked flow (Vch) was stable for the first 40 mins after the animals were killed. Flow rates of 1.25, 2.5, 3.75, 5.0, 7.5, 10.0, and 12.5 mL/sec were then applied at an additional volume of 30, 45, or 60 mL to 34 animals. Vch approximately doubled as the flow rate increased from 1.25 mL/sec to 12.5 mL/sec (p < .001). At the same flow, Vch was higher for an additional volume of 60 mL than 30 mL when the flow was ≥2.5 mL/sec. ConclusionsFrom these data, we conclude that choked flow occurs at intratracheal pressure of less than −20 mm Hg, that Vch is stable for the first 40 mins after the animals are killed, and that Vch is a function of flow rate and initial volume.