Objective: To investigate the effects of different modes of artificial ventilation on lung injury in a dog model of acute respiratory distress syndrome (ARDS), and to evaluate the protective effect of various parameters in mechanical ventilation on lung injury.
Methods: Thirty-six healthy dogs were randomly divided into normal control group (N group), ARDS group (M group) and ventilation group (A-D groups) based on a series of random number. The ARDS dog model was replicated by intratracheal instillation of hydrochloric acid, and mechanical ventilation was carried out according to the following ventilatory protocols. A group: low V(T) (6 ml/kg) with respiratory rate 30/minutes, low inspiratory flow 6 ml.kg(-1).s(-1). B group: large V(T) (20 ml/kg) with respiratory rate 30/minutes, high inspiratory flow 20 ml.kg(-1).s(-1). C group: large V(T) (20 ml/kg) with respiratory rate 15/minutes, high inspiratory flow 17 ml.kg(-1).s(-1). D group: large V(T) (20 ml/kg) with respiratory rate 15/minutes, low inspiratory flow 10 ml.kg(-1).s(-1). Lung mechanical parameters were recorded at 0, 1, 2 and 4 hours after the change in ventilatory protocol. After 4 hours of mechanical ventilation, animals were sacrificed, and the lung was harvested. Lung wet/dry weight ratio (W/D) was measured. Histopathological changes were observed under light microscope, diffuse alveolar damage (DAD) scores was estimated, and polymorphonuclear leucocytes (PMN) count was done. Nuclear factor-KappaB (NF-KappaB) p65 activity was assessed by flow cytometry.
Results: W/D in B group (9.95+/-0.99) was higher than that of A (6.78+/-0.56) and D (7.11+/-0.47) groups (both P<0.01),but there was no significant difference between B and C groups (9.22+/-1.19, P>0.05). DAD scores in B group (12.80+/-1.47) was obvious higher than that of A (7.67+/-1.20) and D (8.83+/-1.17) groups (both P<0.01), but there was no difference compared with C group (11.50+/-1.87, P>0.05). NF-KappaB p65 activity in B group [(33.56+/-2.85)%] was significantly higher than that of A [(10.35+/-0.60)%] and D [(10.79+/-1.02)%] groups, but there was no difference between B and C [(30.87+/-1.16)%] groups.
Conclusion: Large tidal volumes with high inspiratory flow and high respiratory rate may cause severe ventilator induced lung injury (VILI). Reduction of inspiratory flow and respiratory rate with large tidal volume ventilation may provide pulmonary protection.