犬急性肺损伤早期不同通气策略对气体交换和血管外肺水的影响

目的: 探讨急性肺损伤(ALI)早期应用控制性高浓度氧疗、持续气道内正压(CPAP)和双水平气道内正压(BiPAP)不同通气策略对气体交换和血管外肺水的影响。方法: 24只杂种犬在制作油酸ALI模型成功后(PaO₂/FiO₂≤300 mmHg),保持自主呼吸,随机分为:(1)控制性高浓度氧疗组(n=8);(2)CPAP组(n=8);(3)BiPAP组(n=8)。连续记录并计算正常、ALI早期(阳性对照)和干预后1~4 h内各项气体交换和血流动力学指标。结果: 在氧合指数(PaO₂/FiO₂)的改善上,干预后4 h BiPAP组效果最明显(375.83±81.55, P<0.01),其次是CPAP组(327.17±78.82, P<0.01),氧疗组改善不显著(255.00±49.85, P>0.05)。在肺泡死腔与潮气容积之比值[V_D(alv)/V_T]上,氧疗组进一步增大(P<0.01),CPAP组和BiPAP组显著降低(P<0.01)。3种通气策略均可提高氧输送量(DO₂),BiPAP组效果最明显(P<0.01),其次是CPAP组和氧疗组。氧疗组的氧耗量(VO₂)显著增高,氧摄取率(O₂ER)明显高于CPAP组和BiPAP组(P<0.05, P<0.01)。干预后3组肺泡气-动脉血氧分压差[P_(A-a)O₂]较正常基础值和ALI早期均显著增高(P<0.01),3组间两两比较无显著差异(P>0.05)。在肺内分流比例(Qs/Qt)上,BiPAP组改善最明显(P<0.01),其次是CPAP组(P<0.01),氧疗组效果不显著。3组实验动物的肺动脉楔压(PAWP)和心排指数(CI)保持相对稳定。在平均肺动脉压(MPAP)和肺循环阻力指数(PVRI)上CPAP组和BiPAP组均进一步增高(P<0.05, P<0.01)。3组对血管外肺水指数(ELWI)的改善无显著作用(P>0.05)。结论: 在ALI早期,BiPAP和CPAP对于改善气体交换和组织氧合具有积极作用,其中BiPAP效果更为显著。3种通气策略对血管外肺水的改善无显著作用。

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.