[Pathological change of partial liquid ventilation in a rabbit meconium aspiration lung injury model]

To observe the pathological change of partial liquid ventilation (PLV) through establishing the rabbit model of acute lung injury (ALI) induced by meconium aspiration.

Adult, healthy male or female New Zealand white rabbits were randomly allocated into six groups as follows: (1) control group, (2) conventional mechanical ventilation (CMV) group, (3) high-frequency oscillatory ventilation (HFOV) group, (4) CMV combined with PLV group, (5) HFOV combined with PLV group and (6) normal group. The animals were anesthetized with 1% pentobarbital and tracheotomy was performed and endotracheal tube was placed, 20% meconium fluid (3 ml/kg) was quickly injected into the lung through the endotracheal tube and arterial blood gas was analyzed 30 minutes later. ALI was indicated when P/F ratio (PaO2)/FiO(2)) was < or = 300 mm Hg (1 mm Hg = 0.133 kPa) and Cdyn Dynamic Compliance declined by more than 30% of the baseline. The animals were then randomly allocated into one of the 6 groups. In PLV groups (including CMV + PLV and HFOV + PLV) warmed (37 degrees C) and oxygenated perfluorocarbon was slowly instilled into the lungs of the rabbits through the endotracheal tube at a low-dose 3 ml/kg, then set 15-min positive pressure by sacculus proprius to guarantee perfluorocarbon to steadily diffuse in to the lungs. Six hours after ventilation the animals were sacrificed by using overdose of room air instillation via vein. The lungs were taken and fixed in 4% paraformaldehyde (PFA) and were stained with hematoxylin-eosin (HE). Pathological evaluations included inflammatory manifestation, edema and hemorrhage in both alveolar and interstitial area, damages of small airway (alveolar tube and alveolar bursa) and hyaline membrane formation. One way analysis of variance, Student Newman-Keuls (SNK) method and Kruskal-Wallis (K-W) test were used for comparisons.

With the exception of normal group 30 minutes after meconium injections blood gas analysis in different groups showed significant changes and PaO(2)/FiO(2) (< 300 mm Hg), Cdyn declined by more than 60% compared with baseline (P < 0.05). The pathological analysis showed that alveolar and interstitial inflammation, edema, alveolar and interstitial hemorrhage, and small airway damage existed in each group. The hyaline membrane formation was found in one of CMV + PLV group rabbits. The perfluorocarbon-treated animals (CMV + PLV and HFOV + PLV) showed significantly less injury in dependent lung and less damage of small airway (CMV + PLV or HFOV + PLV vs. CMV = 1.1 +/- 0.4 or 0.9 +/- 0.3 vs 2.6 +/- 0.5) compared with the animals of CMV group (P < 0.01). HFOV group (2.1 +/- 0.3) also had less alveolar and interstitial inflammation compared with CMV group (3.0 +/- 0) (P < 0.05), and there was less evidence of alveolar and interstitial edema in the animals treated with HFOV + PLV (1.0 +/- 0.7) compared with CMV (2.0 +/- 0.8) (P < 0.01). Treatment with perfluorocarbon did not result in significant difference in alveolar and interstitial hemorrhage. Compared with CMV and HFOV groups, the groups treated with PLV showed lower mortality of animals (21.4% and 14.3%).

PLV can alleviate the histological damage of acute lung injury induced by meconium aspiration and increased survival chance and therefore PLV would be a useful treatment for MAS. The effectiveness and safety of application of PLV should be evaluated in clinical studies.