肺泡复张后不同呼气末正压和潮气量调节策略对防止肺泡再萎陷效果的实验研究

Positive end-expiratory pressure and tidal volume titration after recruitment maneuver in a canine model of acute respiratory distress syndrome

目的探讨肺泡复张(RM)后再萎陷的机制以及呼气末正压(PEEP)和潮气量(VT)的调节策略。方法健康杂种犬18只,建立油酸所致急性呼吸窘迫综合征(ARDS),行容量控制通气(VCV)、PEEP 16 cm H2O、VT10 m l/kg、通气频率(RR)30次/m in,稳定后作为基础状态(0 m in)。以压力控制通气[气道峰压(PIP)50 cm H2O,PEEP 35 cm H2O,持续60 s]行RM,然后随机分为小VT中等PEEP组(LVMP组,VT10 m l/kg、PEEP 16 cm H2O、RR 30次/m in),小VT低PEEP组(LVLP组,VT10 m l/kg、PEEP 10 cm H2O、RR 30次/m in)和中等VT低PEEP组(MVLP组,VT15 m l/kg、PEEP 10cm H2O、RR 20次/m in)。观察4 h后处死动物,行支气管肺泡灌冼。监测氧合、呼吸力学、血流动力学及肺损伤指标。结果(1)LVMP、LVLP、MVLP组低位拐点(LIP)分别为(16.0±1.3)、(15.8±3.0)、(16.3±1.9)cm H2O。(2)在RM后30、60 m in,LVMP组动脉血氧分压(PaO2)[(371±64)、(365±51)mm Hg]显著高于LVLP组[(243±112)、(240±108)mm Hg]及MVLP组[(242±97)、(232±87)mm Hg,P均<0.05],但直至RM后4 h 3组比较差异无统计学意义;LVLP与MVLP组在RM后各个时间点的PaO2与基础状态比较差异均无统计学意义;MVLP组的通气功能较其他两组显著改善。(3)与基础状态比较,RM后LVMP组平均动脉压(mABP)显著降低,平均肺动脉压(mPAP)显著增加,而其他两组mABP保持稳定,mPAP降低。(4)与基础状态比较,3组PIP和气道平台压(Pp lat)在RM后均显著降低,呼吸系统静态顺应性(Cst)显著改善。在RM后同一时间点比较,MVLP组PIP、Pp lat和Cst均显著好于LVMP组。MVLP组与LVLP组相比,Cst有增加趋势。(5)在相同部位的支气管肺泡灌冼液中,肺损伤指标在各组之间无显著差异。结论与LIP相近的高PEEP有助于防止复张肺泡的再萎陷,但对血流动力学和呼吸力学产生不利影响;早期应用RM能有效“节约”PEEP,并为上调VT提供了较肺泡复张之前更大的空间。

Objective To investigate the mechanisms of alveolar dereeruitment and titration of positive end-expiratory pressure（PEEP） and tidal volume（ VT） after recruitment maneuver（RM） in acute respiratory distress syndrome （ARDS）. Methods Eighteen dogs with oleic acid induced ARDS were ventilated with volume controlled ventilation [ VCV, PEEP 16 cm H2O, VT 10 ml/kg, respiratory rate （RR） 30 breaths/min] and the steady state in this mode was defined as baseline（0 min）. All animals accepted RM by using pressure controlled ventilation [ PEEP 35 cm H2O and peak inspiratory pressure（PIP） 50 cm H2O for 1 min ] and then randomly assigned into three groups and ventilated by VCV for 4 h： low VT and moderate PEEP group（LVMP group,VT 10 ml/kg, PEEP 16 cm H2O,RR 30 breaths/min）,low VT and low PEEP group（LVLP group,VT 10 ml/kg,PEEP 10 cm H2O,RR 30 breaths/min） and moderate VT and low PEEP group（MVLP group,VT 15 ml/kg,PEEP 10 cm H2O,RR 20 breaths/min）. Oxygenation,lung mechanics, hemodynamlcs and lung injury score were measured. Results （ 1 ） The average lower inflection pressure （LIP） was identified as （ 16.0 ± 2. 1 ） cm H2O. （2） PaO2 in the LVMP group [ （ 371 ± 64） mm Hg at 30 min and （365 ±51）mm Hg at 60 mini was higher than that in the LVLP and the MVLP group[ （243 ± 112）, （242 ± 97 ）mm Hg at 30 min and （240 ± 108 ）, （ 232 ± 87 ） mm Hg at 60 min, respectively; all P 〈 0. 05 ], but no significant differences were observed among three groups from the second hour after RM to the end of the experiment. Better ventilation profiles were observed in the MVLP group. （3）Compared with baseline, marked cardiac compromise with higher airway plateau pressure （Pplat） and lower static respiratory compliance（Cst） were found in the LVMP group,while improvement was observed in other two groups. Cst in the MVLP group was slightly higher than that in the LVLP group. （4） No significant differences of lung injury were found from bronchoalveolar lavage fluid（BALF） analysis. Conclusions Higher PEEP close to LIP maybe useful in preventing alveolar recollapse and improving oxygenation,but harmful to hemodynamics and may increase the risk of lung jury. Lower PEEP combined with moderate tidal volume after RM may be a more reasonable approach than conventional lung protective ventilation.