CONCEALED AIR LEAK ASSOCIATED WITH LARGE TIDAL VOLUMES IN PARTIAL LIQUID VENTILATION

Current ventilator strategies aim at maintaining an open lung and limi ting both peak inspiratory pressures and tidal volumes to avoid alveol ar distension. Perfluorocarbons, as well as being excellent solvents f or oxygen and carbon dioxide, have the unique properties of being able to recruit dependent lung regions and improve pulmonary mechanics. Op timal ventilator strategies for partial liquid ventilation (PLV) have not yet been clearly defined. In the surfactant-depleted rabbit model, an approach involving a large tidal volume (VT) (15 ml/kg) and lung f illed to FRC with perfluorocarbon (PFC) was compared with strategies i nvolving a moderate VT (9 ml/kg) and partially filled lung (6 ml/kg), a moderate VT (9 ml/kg) and lung filled to FRC with PFC, and a large V T(15 ml/kg) and partially filled lung (6 ml/kg). PEEP was maintained a t 5 cm H2O except in the moderate VT, partial-filling group, in which a PEEP of 9 cm H2O was used to maintain the rabbits for the duration o f the experiment. Oxygenation was satisfactory in all groups, and peak inspiratory pressures were not significantly different. However, five of the 13 animals in the large-VT, PFC-filled lung group died of a pn eumothorax prior to completion of the experiment. Of the eight animals in this group surviving the experiment, two had radiographic evidence of pneumothoraces, with an additional three animals having autopsy ev idence of air leak. Of the 22 animals in the other groups, all survive d with the exception of a single rabbit in the large VT, partial-filli ng group, which had both radiographic and autopsy evidence of air leak . We conclude that there is a significant risk of barotrauma in a PLV strategy in which a large VT is used in association with a lung filled to FRC with perfluorocarbon. Adequate gas exchange can be achieved wi th alternative ventilation strategies in combination with PLV.