The Experimental Study On The Safety In Recruitment Maneuver In ARDS Sheep Model

1 Study of acute respiratory distress syndrome sheep model inducedby tepid saline lavage via bronchofiberscope.Objective: To research the feasibility of the method to set up a early acuterespiratory distress syndrome(ARDS) sheep model induced by tepid saline lavage viabronchofiberscope.Methods: 26 healthy adult sheep were anesthetized and ventilated, and then ARDSsheep model was induced by tepid saline bronchoalveolar lavage usingbronchofiberscope. Recorded the intake and output volume and oxygenation index(OI) as well. When OI<150mmHg, CT scan was performed to see the change of lungstructure. Pulmonary mechanics, hemodynamics and dynamic oxygenation wereobserved before and 2 hours after lavage.Results: All 26 sheep maintained stable in state of ARDS in 2 hours after lavage, themean lavage volume was 12.0±3.6ml/Kg and the positive balance was122.0±35.9ml. Oxygenation index(OI) , dynamic pulmonary compliance(Cdyn)decreased significantly after lavage, extravascular lung water index (EVLWI)increased significantly (P<0.05). Cardiac index(CI) and intrathoracic blood volumeindex (ITBVI) had no change before and after lavage.Conclusion: Lung warm saline lavage via bronchofiberscope is a feasible, safe andreproductive method to modeling ARDS, it is the suitable for early ARDSexperimental study.2 The experimental study of the safety in recruitment maneuver inARDS sheep modelObjective: To study the effects on hemodynamics and lung structure when lung recruitment strategy was performed via sustained inflation (SI) in acute respiratory ditress syndrome (ARDS) sheep model, so that to find the safe range of pressure in SI procedure.Methods: 14 anaesthetized sheep were performed tracheotomy, and then acute lung injury was induced by saline lavage through branchifibroscope, following quasi-static P-V curves was drawn by low flow technique, then found the upper inflection point (UIP) and the lower inflection point (LIP), and selected 5cmH₂O below UIP, UIP, 10cmH₂O above UIP, 20cmH₂O above UIP as the peak pressure for SI. 14 sheep were randomized to four groups (U-5, U+0, U+10, U+20), the duration of SI was 60s. Hemodynamics and oxygenation index was monitored and recorded during and after SI until the study was over two hours later, then CT scan and lung tissue biopsy were performed.Results: Pneumothorax was found in U+20 group, result in the death of sheep;Hemodynamics was affected significantly in other groups during SI. In U+10 group, central venous pressure (CVP), cardiac output (CO) and mean arterial pressure (MAP) was exacerbated at 10s when SI begun, and recovered slowly after SI;In U+0 group and U-5 group, the entire procedure can be finished, also seen the less increase in CVP and decrease in CO, and came back in 30s and 15s respectively. Besides U+0 groups, oxygenation was significantly impoved in each group;stable hemodynamics was also seen in each group. The CT scans shewed the trend ofrecover, the biopsy showed bullous emphysema in U+0 and U+10 group. Conclusion: The impairment to the hemodynamics and lung structure should be emphasized when recruitment maneuver was performed in ARDS patients, our study demonstrates that the pressure should be limited between 5cmH2O below UIP and UIP, no obvious effect to hemodynamics was found in this range and less injury to lung structure.