Partial liquid ventilation ventilates better than gas ventilation

Partial liquid ventilation (PLV) improves oxygenation in several models of lung injury. However, PLV has only been compared with conventional gas ventilation (GV) with low PEEP. Both PLV and GV can markedly improve oxygenation when PEEP is set above the lower corner pressure (Plc) on the inspiratory pressure-volume (P-V) curve of the total respiratory system. We questioned if the use of PEEP set above the Plc during PLV and GV would result in similar gas exchange. Lung injury was induced in 12 sheep by saline lavage before randomization to PLV (n = 6) or GV (n = 6). Animals in the PLV group were filled with perflubron (22 ml/kg) until a meniscus at the teeth was observed. Both groups were then ventilated with pressure control (FI(O(2)), 1.0; rate, 20/min; I:E, 1:1) and PEEP (1 cm H(2)O above the Plc on the inspiratory P-V curve). Peak inspiratory pressure (PIP) was limited to 35 cm H(2)O. Animals were ventilated for 5 h and then killed for histologic examinations. All 12 animals survived the 5-h ventilation period. After increasing PEEP above Plc, Pa(O(2)) increased significantly (p < 0.01) in both the GV and the PLV groups, but it did not differ significantly between groups (p = 0.86) at any time during the experiment. Pa(CO(2)) and VD/VT in GV increased markedly throughout the experiment after increasing PEEP (p < 0.001), but there was no significant change in Pa(CO(2)) in PLV (p = 0.13). Mean arterial blood pressure, mean pulmonary artery pressure, pulmonary artery occlusion pressure, and central venous pressure, increased and SVR decreased in GV (p < 0.05). The extent and the severity of lung injury in the dependent regions was greater in the GV group (p < 0.05). Both PLV and GV improved oxygenation, but PLV resulted in better ventilation than GV while preserving lung structure when PEEP was set 1 cm H(2)O above the Plc and PIP limited to 35 cm H(2)O.