Boehme Stefan, Bentley Alexander H, Hartmann Erik K, Chang Shi, Erdoes Gabor, Prinzing Anatol, Hagmann Michael, Baumgardner James E, Ullrich Roman, Markstaller Klaus, David Matthias
1Department of Anesthesia, General Intensive Care, and Pain Management, Medical University Vienna, Vienna, Austria. 2Department of Anesthesiology, Medical Center of the Johannes-Gutenberg University Mainz, Mainz, Germany. 3Beijing Institute of Pharmacology and Toxicology, National Beijing Center for Drug Safety Evaluation and Research, Beijing, People's Republic of China. 4Department of Cardiovascular Surgery, German Heart Center Munich, Munich, Germany. 5Center for Medical Statistics, Informatics, and Intelligent Systems, Medical University Vienna, Vienna, Austria. 6Oscillogy LLC, Folsom, PA.
Crit Care Med. 2015 Mar;43(3):e65-74. doi: 10.1097/CCM.0000000000000788.
Cyclic recruitment and derecruitment of atelectasis can occur during mechanical ventilation, especially in injured lungs. Experimentally, cyclic recruitment and derecruitment can be quantified by respiration-dependent changes in PaO2 (ΔPaO2), reflecting the varying intrapulmonary shunt fraction within the respiratory cycle. This study investigated the effect of inspiration to expiration ratio upon ΔPaO2 and Horowitz index.
Prospective randomized study.
Laboratory investigation.
Piglets, average weight 30 ± 2 kg.
At respiratory rate 6 breaths/min, end-inspiratory pressure (Pendinsp) 40 cm H2O, positive end-expiratory pressure 5 cm H2O, and FIO2 1.0, measurements were performed at randomly set inspiration to expiration ratios during baseline healthy and mild surfactant depletion injury. Lung damage was titrated by repetitive surfactant washout to induce maximal cyclic recruitment and derecruitment as measured by multifrequency phase fluorimetry. Regional ventilation distribution was evaluated by electrical impedance tomography. Step changes in airway pressure from 5 to 40 cm H2O and vice versa were performed after lavage to calculate PO2-based recruitment and derecruitment time constants (TAU).
In baseline healthy, cyclic recruitment and derecruitment could not be provoked, whereas in model acute respiratory distress syndrome, the highest ΔPaO2 were routinely detected at an inspiration to expiration ratio of 1:4 (range, 52-277 torr [6.9-36.9 kPa]). Shorter expiration time reduced cyclic recruitment and derecruitment significantly (158 ± 85 torr [21.1 ± 11.3 kPa] [inspiration to expiration ratio, 1:4]; 25 ± 12 torr [3.3 ± 1.6 kPa] [inspiration to expiration ratio, 4:1]; p < 0.0001), whereas the PaO2/FIO2 ratio increased (267 ± 50 [inspiration to expiration ratio, 1:4]; 424 ± 53 [inspiration to expiration ratio, 4:1]; p < 0.0001). Correspondingly, regional ventilation redistributed toward dependent lung regions (p < 0.0001). Recruitment was much faster (TAU: fast 1.6 s [78%]; slow 9.2 s) than derecruitment (TAU: fast 3.1 s [87%]; slow 17.7 s) (p = 0.0078).
Inverse ratio ventilation minimizes cyclic recruitment and derecruitment of atelectasis in an experimental model of surfactant-depleted pigs. Time constants for recruitment and derecruitment, and regional ventilation distribution, reflect these findings and highlight the time dependency of cyclic recruitment and derecruitment.
在机械通气过程中，尤其是在受损肺脏中，肺不张可能会周期性地出现复张和萎陷。在实验中，周期性复张和萎陷可通过动脉血氧分压（ΔPaO₂）的呼吸依赖性变化进行量化，这反映了呼吸周期内肺内分流分数的变化。本研究调查了吸呼比对ΔPaO₂和霍洛维茨指数的影响。
前瞻性随机研究。
实验室研究。
平均体重30±2千克的仔猪。
在呼吸频率为6次/分钟、吸气末压力（Pendinsp）为40厘米水柱、呼气末正压为5厘米水柱且吸入氧分数为1.0的条件下，在基线健康状态和轻度表面活性剂耗竭性损伤期间，以随机设定的吸呼比进行测量。通过重复冲洗表面活性剂来滴定肺损伤，以诱导最大程度的周期性复张和萎陷，通过多频相位荧光法进行测量。通过电阻抗断层扫描评估区域通气分布。在灌洗后，将气道压力从5厘米水柱逐步升至40厘米水柱，然后再降至5厘米水柱，以计算基于氧分压的复张和萎陷时间常数（TAU）。
在基线健康状态下，无法诱发周期性复张和萎陷，而在急性呼吸窘迫综合征模型中，在吸呼比为1:4（范围为52 - 277托[6.9 - 36.9千帕]）时，通常会检测到最高的ΔPaO₂。较短的呼气时间显著减少了周期性复张和萎陷（158±85托[21.1±11.3千帕][吸呼比，1:4]；25±12托[3.3±1.6千帕][吸呼比，4:1]；p<0.0001），而动脉血氧分压/吸入氧分数比值增加（267±50[吸呼比，1:4]；424±53[吸呼比，4:1]；p<0.0001）。相应地，区域通气重新分布至肺低垂区域（p<0.0001）。复张比萎陷快得多（TAU：快速1.6秒[78%]；慢速9.2秒）（TAU：快速3.1秒[87%]；慢速17.7秒）（p = 0.0078）。
反比通气可使表面活性剂耗竭猪的实验模型中肺不张的周期性复张和萎陷降至最低。复张和萎陷的时间常数以及区域通气分布反映了这些结果，并突出了周期性复张和萎陷的时间依赖性。
