Application Of Lung Ultrasound In Recruitment Maneuver On Rabbits With Acute Respiratory Distress Syndrome

Objective:1. Establishment of saline-lavaged rabbits with acute respiratory distress syndrome (ARDS) and lung ultrasound evaluation protocol.2. Verification of the guiding role of ultrasound reaeration score in recruitment maneuver (RM).3. Investigation of lung ultrasound guided positive end expiratory pressure (PEEP) titration after recruitment maneuver.Design:Part Ⅰ:12rabbits with saline lavaged lung injury model were divided into2groups, which referred to lung ultrasound guided RM group (LUS group) and maximal oxygenation guided RM group (OXY group). ARDS model-based lung ultrasound evaluation protocol were established and applied in the modeling process. Recruitment maneuver were applied according to step-wise incremental PEEP method in both groups, while the OXY group consider PaO2+PaCO2≥400mmHg as recruitment destination, and the LUS group consider the reaeration score which stop increasing as target. Lung ultrasound evaluation result, arterial oxygenation, respiratory mechanical parameters, Smith’s pathology score and wet/dry ratio were compared between two groups.Part Ⅱ:6rabbits with saline lavaged lung injury model and underwent pressure control ventilation (PCV) lung recruitment followed by2cmH2O step-wise optimal PEEP titration, with the destination of PaO2+PaCO2≤380mmHg. Novel method of lung ultrasound guided PEEP titration was proposed based on the incident evaluation result. Destination comparison, which included lung ultrasound findings and arterial oxygenation level, was made between the LUS and OXY methods.Result:Part Ⅰ: 1. Lung ultrasound can effectively evaluate the change of aeration level in saline-lavaged rabbit ARDS model. According to the result, during the modeling process, lung consolidation first appeared in the posterior lung, associated with various decreasing of aeration level in anterior and medial lung.2.5cmH20PEEP trial can improve oxygenation level significantly (50±10mmHg v. s.93±40mmHg, p<0.05), dynamic compliance (0.8±0.2ml/cmH2O v. s.1.1±0.3ml/cmH20) and dead space shunt (0.87±0.05vs.0.79±0.06,p<0.05). However no significant improvement could be observed according to the ultrasound evaluation, which limited in the anterior and medial zone.3. During the recruitment maneuver, destinations in both groups were reached. Opening pressure (8.7±2.1cmH20vs.23.4±3.4cmH20, p<0.05) and arterial oxygenation (465±57mmHg vs.552±77mmHg, p<0.05) in LUS group were significantly higher than that in OXY group. Ultrasound reaeration score in LUS group also significantly increased (6.5±1.6vs.13.8±3.0pts), which indicated that the aeration level were further improved. Lung compliance and dead space shunt between two groups did not show significant difference, as well as the Smith pathology score and tissue wet/dry ratio.Part Ⅱ:1. During the optimal PEEP titration, destination defined by Pa02+PaC02≤380mmHg could be reached in saline-lavaged rabbit ARDS model. Ultrasound reaeration score decreased continuously, and according to ultrasound result, lung consolidation could be observed in the level of optimal PEEP.2. Sudden change (decrease≥50%) could be observed in reaeration score dynamic change in the titration process, while the PEEP level before the sudden change lay above the optimal PEEP (PEEP before the sudden change vs. optimal PEEP:12.0+2.2cmH20vs.9.3±2.1cmH20,p<0.05). Part III:1. Seven patients were enrolled in the observational study. Similar to the result of animal experiment, sudden change could also be observed in reaeration score dynamic change in the titration process of ALI/ARDS patients, while the PEEP level before the sudden change mostly (4/7cases) lay above the optimal PEEP (PEEP before the sudden change vs. optimal PEEP:14.1±1.0cmH2O vs.12.4±2.3cmH2O,p<0.05).Conclusions:1. Lung ultrasound can effectively evaluate the change of aeration level in the process of model installation, recruitment maneuver and optimal PEEP titration in saline-lavaged rabbit ARDS model.2. After model installation,5cmH20PEEP trial could significantly improve the arterial oxygenation, while dynamic change in ultrasound observation, which was limited in anterior and medial lung, did not indicate obviour change.3. Compared with maximal oxygenation guided method, lung ultrasound guided method required higher opening pressure and resulted in improved oxygenation and reaeration score, which indicated that further improvement in lung aeration level. Respiratory mechanical parameter and lung pathology result did not show lung damage aggravated.4. Compared with maximal oxygenation guided method, lung ultrasound guided recruitment improved aeration in all regions, which indicated that lung heterogeneity in ALI/ARDS was improved effectively.5. During the optimal PEEP titration, ultrasound reaeration score decreased continuously, and sudden change (decrease≥50%) could be observed in reaeration score dynamic change in the PEEP titration process, while the PEEP level before the sudden change lay above the optimal PEEP, which indicated that lung aeration significantly decreased before titration to the optimal PEEP according to the maximal oxygenation.6. Based on the observation in this study, novel method in optimal PEEP titration post RM was proposed and validated in pilot clinical study, and further application in clinical settings would be promising.