Oxygenation and lung morphology in a rabbit pediatric ARDS- model under high peak pressure ventilation plus nitric oxide and surfactant compared withveno-venous ECMO

The aim of the study is to investigate which of two treatment options of sa line lavage induced ARDS in rabbits is better in terms of oxygenation and p revention of barotrauma: combined high peak pressure ventilation with surfa ctant administration and inhaled nitric oxide or veno-venous ECMO combined with low peak inspiratory pressure ventilation. Materials and Methods: After saline lavage (10 cc/kg repeated as long as fo amy retrieval was observed) two combined therapeutic strategies were examin ed: ventilation with high inspiratory pressures (35 cm H2O) with additional exogenous surfactant administration (100 mg/kg) and inhaled nitric oxide ( 10 PPM) (n=5, group 1) and low inspiratory pressure (20 cm H2O) ventilation under veno-venous ECMO support (n=5, group 2). The FiO(2) was maintained a t 1.0 in both groups. The paO(2)/FiO(2) ratio was calculated in 30 minute i ntervals for 4 hours. After that the animals were sacrificed and the lungs examined macro- and microscopically. Aeration was described in a semiquanti tative method using the alveolar expansion index. Oxygenation in group I wa s significantly better than in group 2 if increased significantly after sur factant but not after additional nitric oxide administration. However, the lungs in group I showed severe signs of baro/ergotrauma (Hyaline membranes, air leaks, infiltration of polymorphonuclear (PMN) granulocytes and macrop hages, break down of alveolar capillary membranes) after 4 hrs of combined therapy whereas the lungs in group 2 appeared normal. Adding surfactant and NO to a high tidal volume ventilation improved oxygenation, but did not pr event baro/ergotrauma. Ventilation with low inspiratory pressures combined with ECMO caused little baro/ergotrauma but adequate oxygenation could not be achieved, probably due to anatomical features of the rabbit which do not allow appropriate blood flow within the ECMO-circuit.