不同潮气量机械通气对急性呼吸窘迫综合征家兔凝血/纤溶的影响

Effects of mechanical ventilation with different tidal volumes on coagulation/fibrinolysis in rabbits with acute respiratory distress syndrome

目的：观察不同潮气量（VT）机械通气对油酸及内毒素二次打击诱导急性呼吸窘迫综合征（ARDS）家兔凝血/纤溶的影响。方法按随机数字表法将40只雄性家兔分为假手术组、模型组、小VT组（6 mL/kg）、常规VT组（10 mL/kg）及大VT组（15 mL/kg），每组8只。采用耳缘静脉序贯注射油酸0.1 mL/kg及内毒素脂多糖（LPS）500μg/kg的方法制备ARDS动物模型；假手术组仅给予等量生理盐水。不同VT组均于制模后行机械通气，以LPS注射后6 h为实验终点。于注射LPS后30 min、360 min取颈动脉血测定动脉血氧分压并计算氧合指数；于注射LPS后5、120、240、360 min取颈内静脉血，检测活化部分凝血活酶时间（APTT）、凝血酶原时间（PT）、纤维蛋白原（Fib）、抗凝血酶Ⅲ（AT-Ⅲ）；实验结束时抽血并处死家兔，测定血清Ⅲ型前胶原肽（PⅢP）、纤溶酶原激活物抑制剂1（PAI-1）及肺组织PⅢP含量，测定肺组织湿/干质量（W/D）比值。结果与假手术组比较，模型组30 min、360 min时氧合指数显著降低，肺W/D比值显著升高；PT、APTT 5 min时明显缩短，此后进行性延长；Fib、AT-Ⅲ于5 min时无明显变化，之后均明显降低；血清PAI-1、PⅢP及肺组织PⅢP均显著升高。各VT组氧合指数与模型组比较差异无统计学意义，但小VT组有升高趋势。小VT组肺W/D比值最低（5.09±0.19），明显低于模型组（6.02±0.27，P＜0.01）；大VT组为最高（6.27±0.32）。各VT组PT、APTT均进行性延长，Fib、AT-Ⅲ进行性下降；而小VT组120 min起PT、APTT较模型组明显缩短〔PT（s）：120 min：8.90±0.28比11.43±0.28，240 min：9.18±0.21比11.99±0.50，360 min：9.25±0.15比12.49±0.29；APTT（s）：120 min：69.09±3.91比76.08±4.21，240 min：67.53±2.14比79.71±2.25，360 min：66.95±1.13比83.21±4.01，均P＜0.05〕，Fib（g/L）较模型组明显升高（120 min：3.80±0.09比3.38±0.15，240 min：3.91±0.05比2.47±0.16，360 min：4.06±0.13比2.39±0.16，均P＜0.05），AT-Ⅲ则与模型组差异无统计学意义，血清PAI-1、PⅢP及肺组织PⅢP含量明显降低〔血清PAI-1（ng/L）：1.14±0.26比1.63±0.91，血清PⅢP（ng/L）：1.62±0.52比2.91±0.64，肺组织PⅢP（ng/L）：4.40±0.58比5.75±0.47，均P＜0.01〕。常规VT组各指标变化趋势和幅度均较小VT组小，PT于120 min及360 min、 APTT于240 min及360 min时明显短于模型组，Fib于120 min及240 min时明显高于模型组（均P＜0.05）；AT-Ⅲ、血清PAI-1和PⅢP及肺组织PⅢP含量与模型组比较差异均无统计学意义。而大VT组360 min时PT和APTT较模型组明显延长，360 min时Fib明显低于模型组，肺组织PⅢP明显高于模型组。结论二次打击致ARDS家兔凝血功能由高凝很快转为低凝，且存在纤溶抑制；机械通气时使用小VT可明显改善凝血和纤溶，常规VT无此作用，而大VT则可明显加重凝血障碍及纤溶抑制。

Objective To observe the effects of mechanical ventilation with different tidal volumes （VT） on coagulability and fibrinolytic characteristics in rabbits with acute respiratory distress syndrome （ARDS） induced by two-hits with oleic acid （OA） and lipopolysaccharide （LPS）.Methods Forty healthy adult male rabbits were randomly divided into five groups （8 rabbits in each group）： sham operation group, model group, low VT group （6 mL/kg）, rontine VT group （10 mL/kg）, high VT group （15 mL/kg）. ARDS model was reproduced by sequential injection of 0.1 mL/kg OA and 500μg/kg LPS via auricular vein, and the rabbits in sham operation group received normal saline in same volume. Mechanical ventilation was performed in different VT groups after model reproduction, and the end of the experiment was determined as 6 hours after LPS injection. Blood was collected from the carotid artery at 30 minutes and 360 minutes after LPS injection, with which arterial partial pressure of oxygen （PaO2） was determined, and oxygenation index was calculated. Internal jugular vein blood was collected at 5, 120, 240, and 360 minutes after LPS injection, and activated partial thromboplastin time （APTT）, prothrombin time （PT）, fibrinogen （Fib） and antithrombinⅢ（AT-Ⅲ） were determined. The blood was collected at the end of the experiment, and then the rabbits were sacrificed, and serum levels of procollagen typeⅢ （PⅢP）, plasminogen activator inhibitor-1 （PAI-1） as well as PⅢP level in lung tissue were determined. The wet/dry weight ratio （W/D） of lung tissues was calculated.Results Compared with sham operation group, oxygenation index at both 30 minutes and 360 minutes were significantly decreased in model group, while W/D ratio was significantly increased. PT and APTT at 5 minutes were significantly shortened followed by a gradual increase. Fib and AT-Ⅲ showed no change at 5 minutes followed by a gradual decrease, while serum PAI-1 and PⅢP as well as PⅢP in lung tissue were significantly increased. There was no significant difference in oxygenation index between all VT groups and model group, with a tendency to increase in low VT group. W/D ratio in low VT group was the lowest （5.09±0.19）, and it was significantly lower than that of the model group （6.02±0.27, 〈 0.01）, while it was the highest in high VT group （6.27±0.32）. PT and APTT in all VT groups were gradually prolonged, and Fib and AT-Ⅲ were gradually decreased. PT and APTT in low VT group were significantly shorter than those in model group from 120 minutes on [PT （s）： 120 minutes： 8.90±0.28 vs. 11.43±0.28, 240 minutes： 9.18±0.21 vs. 11.99±0.50, 360 minutes： 9.25±0.15 vs. 12.49±0.29; APTT （s）： 120 minutes： 69.09±3.91 vs. 76.08±4.21, 240 minutes： 67.53±2.14 vs. 79.71±2.25, 360 minutes： 66.95±1.13 vs. 83.21±4.01, all〈 0.05], Fib （g/L） was significantly elevated （120 minutes： 3.80±0.09 vs. 3.38±0.15, 240 minutes： 3.91±0.05 vs. 2.47±0.16, 360 minutes：4.06±0.13 vs. 2.39±0.16, all〈 0.05）, and no significant difference was found in AT-Ⅲ. Serum contents of PAI-1 and PⅢP as well as PⅢP in lung tissue were significantly lowered [serum PAI-1 （ng/L）： 1.14±0.26 vs. 1.63±0.91, serum PⅢP （ng/L）： 1.62±0.52 vs. 2.91±0.64, lung PⅢP （ng/L）： 4.40±0.58 vs. 5.75±0.47, all〈 0.01]. The change tendency of all parameters in routine VT group was lower than that in low VT group, PT at 120 minutes and 360 minutes, APTT at 240 minutes and 360 minutes was significantly shorter than that in model group, and Fib at 120 minutes and 240 minutes were significantly higher than those in model group （all〈 0.05）. No significant difference was found in AT-Ⅲ, serum PAI-1 and PⅢP as well as lung PⅢP as compared with model group. PT and APTT at 360 minutes in high VT group were significantly longer than those in model group, Fib at 360 minutes was significantly lower than that in model group, and lung PⅢP was significantly higher than that in model group. Conclusions There are some important changes in coagulability which changes from a hyper state into a hypo coagulate state, while fibrinolysis is inhibited during the pathological process of ARDS produced by two-hit of OA and LPS. Mechanical ventilation with low VT can obviously improve coagulability and fibrinolytic status, while ventilation with routine VT has little effect on coagulability and fibrinolytic status. Mechanical ventilation with high VT, however, will greatly deteriorate the coagulability and fibrinolytic function in ARDS.