Effects of different ventilation strategies on gas exchange and extravascular lung water during early stage of acute lung injury in a canine model

AIM: To evaluate the effects of different ventilation strategies on gas exchange and extravascular lung water during early stage of acute lung injury (ALI). METHODS: Upon the establishment of oleic acid-induced ALI (diagnostic standard: PaO₂/FiO₂ ≤ 300 mmHg), 24 adult mongrel dogs were randomly divided into 3 groups (n=8 each) according to different ventilation strategies: controlling high-concentration oxygen therapy (O₂) group, continuous positive airway pressure (CPAP) group and bi-level positive airway pressure (BiPAP) group. The parameters of gas exchange and hemodynamics including the values of normal baseline, at ALI early stage (positive control) and from 1 to 4 h after treatment were recorded continuously. RESULTS: Compared with the value at the beginning of ALI, after 4 h of artificial ventilation, the improvement in oxygenation index (PaO₂/FiO₂) in BiPAP group (375.83±81.55, P<0.01) and CPAP group (327.17±78.82, P<0.01) were better than that in O₂ group (255.00±49.85, P>0.05). The ratio of alveolar dead space to tidal volume V_D(alv)/V_T]in O₂ group further increased (P<0.01), while it obviously declined in CPAP group and BiPAP group (P<0.01). Oxygen delivery (DO₂) in BiPAP group (P<0.01) was much higher than that in CPAP group and O₂ group, while oxygen consumption (VO₂) and oxygen extraction rate (O₂ER) in O₂ group were evidently higher than those in CPAP group and BiPAP group (P<0.05, P<0.01). After treatment, the alveolar-arterial oxygen differences P_(A-a)O₂] of the 3 ventilation groups were significantly higher than the normal baseline values and the values at early ALI stage (P<0.01). BiPAP and CPAP greatly reduced the ratio of shunted blood to total perfusion (Qs/Qt) as compared with O₂ group (P<0.01). Some parameters including pulmonary arterial wedge pressure (PAWP) and index of cardiac output (CI) kept stable, while mean pulmonary arterial pressure (MPAP) and pulmonary vascular resistance index (PVRI) further increased in CPAP group and BiPAP group (P<0.05,P<0.01). Three ventilation strategies did not effectively control the increase in extravascular lung water index (ELWI). CONCLUSION: During early stage of ALI, BiPAP and CPAP make active effects on improving gas exchange and tissue oxygenation. BiPAP displays more significant therapeutic effect than CPAP and oxygen therapy. The 3 ventilation strategies have no obvious effects on reducing extravascular lung water.