The Protective Effects Of Low Tidal Volume Ventilation In A Rabbit Model Of Oleic Acid-Induced Acute Lung Injury

Objectives: To determine the protective effects of low tidal volume ventilation on the oleic acid-induced acute lung injury and the pathological changes of lung ventilated with 100% oxygen.Methods: Thirty healthy New Zealand white rabbits were randomly divided into five groups: Control group (CTR), low tidal volume non-pure oxygen group (LTNP), high tidal volume non-pure oxygen group (HTNP), low tidal volume pure oxygen group (LTP) and high tidal volume pure oxygen group (HTP). After 2 hours infused by oleic acid (OA, 0.1ml/kg), the rabbit model of acute lung injury was built. Mechanical ventilation was employed in the experiment groups with CMV ( V\_T 15ml/kg for the high tidal volume groups, 8ml/kg for the low tidal volume groups; respiratory rate was 30 per minute; I:E was 1:2; FIO\₂ was 50 percent for the non-pure groups, 100 percent for pure oxygen groups; PEEP 5cmH\₂O), the respiratory rate was adjusted to keep PaCO\₂ between 35 and 45 mmHg. During the period that the rabbits were ventilated, PIP, MAP and arterial blood gas analysis were recorded. Rabbits were killed after 5 hours ventilation when the whole lungs were acquired and weighted, lungs pathological histology and electron ultrastructure were obtained. The supernatant of BALF was analyzed for protein content. The rabbits in CTR group were not ventilated .Results: 1. At the end of experiments, PIP was higher in the high tidal volume groupsthan that in the low tidal volume groups(P<0.01). PIP was higher in the LTP group than that in the LTNP group(P<0.01). 2. At the end of experments, the level of MAP in the HTNP and HTP groups markedly decreased compared with that of the pro-experment(P<0.01). 3.The lung coefficient ( wet weight /body weight)was higher in the HTNP group than that in the CTR and LTNP group (P<0.01). It was higher in the HTP group than that in the LTP group(P<0.01),but there was no significant difference between CTR , LTNP and LTP groups(P>0.05). 4. The protein content of BALF was higher in the HTNP group than that in the LTNP and CTR group (P<0.01), It was higher in the HTP than that in the LTP group(P<0.01) and it was higher in the pure oxygen group than that in the non-pure oxygen group. 5. In the pathologic histology, the changes were lighter in the LTNP group than that in the CTR group, but the alveolar congestion, lung hemorrhage, lung necrosis and inflammatory cells infiltration, the high tidal volume groups(including HTNP and HTP group) were severer than that in the low tidal volume groups. The alveolar edema and lung hemorrhage were the severest in the HTP group. The lung necrosis and the inflammatory cells infiltration were the severest in the HTP and HTNP group. Under electron microscopy, the pathological changes were severer in the HTNP group than that in the LTNP group, Plasma contents and blood cells leaking into alveolar cavities were observed. A number of neutrophil or eosinophil granulocytes were infiltrated into the interstitium . The number of the lamellar bodies of Pneumocyte II epithellum was decreased or depleted. The capillaries in the HTP group were blocked by granules and platelets, as well as classical thrombosis . There were a lot of fibrinoproliferation in the alveolar septa. The pathologic changes in the pure oxygen groups were severer than that in the non-pure oxygen groups. Conclusions: 1. The low tidal volume ventilation has protective effects on the oleic acid-induced acute lung injury. 2.The high tidal volume ventilation exacerbated the lung injury. 3.The pathological changes of the pure oxygen groups were severer than that of the non-pure oxygen groups. Only ventilated for 5 hours, a number offibrinoproliferation were discovered in the alveolar septa. 4. It is suggested that the non-pure oxygen animal model be used in the study of the respiratory failure.