1 Department of Radiology and.
2 Department of Anesthesiology and Critical Care, University of Pennsylvania, Philadelphia, Pennsylvania.
Am J Respir Crit Care Med. 2018 Jul 15;198(2):197-207. doi: 10.1164/rccm.201708-1728OC.
It remains unclear how prone positioning improves survival in acute respiratory distress syndrome. Using serial computed tomography (CT), we previously reported that "unstable" inflation (i.e., partial aeration with large tidal density swings, indicating increased local strain) is associated with injury progression.
We prospectively tested whether prone position contains the early propagation of experimental lung injury by stabilizing inflation.
Injury was induced by tracheal hydrochloric acid in rats; after randomization to supine or prone position, injurious ventilation was commenced using high tidal volume and low positive end-expiratory pressure. Paired end-inspiratory (EI) and end-expiratory (EE) CT scans were acquired at baseline and hourly up to 3 hours. Each sequential pair (EI, EE) of CT images was superimposed in parametric response maps to analyze inflation. Unstable inflation was then measured in each voxel in both dependent and nondependent lung. In addition, five pigs were imaged (EI and EE) prone versus supine, before and (1 hour) after hydrochloric acid aspiration.
In rats, prone position limited lung injury propagation and increased survival (11/12 vs. 7/12 supine; P = 0.01). EI-EE densities, respiratory mechanics, and blood gases deteriorated more in supine versus prone rats. At baseline, more voxels with unstable inflation occurred in dependent versus nondependent regions when supine (41 ± 6% vs. 18 ± 7%; P < 0.01) but not when prone. In supine pigs, unstable inflation predominated in dorsal regions and was attenuated by prone positioning.
Prone position limits the radiologic progression of early lung injury. Minimizing unstable inflation in this setting may alleviate the burden of acute respiratory distress syndrome.
俯卧位如何提高急性呼吸窘迫综合征患者的生存率仍不清楚。我们之前通过连续计算机断层扫描（CT）报道，“不稳定”充气（即局部充气不均匀伴大潮气量波动，表明局部应变增加）与损伤进展有关。
我们前瞻性地测试俯卧位是否通过稳定充气来抑制实验性肺损伤的早期进展。
通过气管内盐酸诱导大鼠肺损伤；随机分为仰卧位或俯卧位后，采用大潮气量和低呼气末正压开始损伤性通气。在基线和 1 小时至 3 小时期间，每小时采集一次吸气末（EI）和呼气末（EE）的 CT 扫描。将每对连续的 CT 图像（EI、EE）叠加在参数响应图中以分析充气情况。在依赖和非依赖肺的每个体素中测量不稳定充气。此外，对五头猪进行成像（EI 和 EE），仰卧位和俯卧位，在盐酸吸入前后。
在大鼠中，俯卧位限制了肺损伤的传播并提高了生存率（11/12 例俯卧位比 7/12 例仰卧位；P=0.01）。仰卧位大鼠的 EI-EE 密度、呼吸力学和血气恶化程度高于俯卧位大鼠。在基线时，仰卧位时依赖区比非依赖区有更多的不稳定充气体素（41%±6%比 18%±7%；P<0.01），但俯卧位时则不然。在仰卧位猪中，不稳定充气主要发生在背部区域，俯卧位可减轻其发生。
俯卧位限制了早期肺损伤的影像学进展。在这种情况下，尽量减少不稳定充气可能会减轻急性呼吸窘迫综合征的负担。
