University of Wuerzburg, Department of Anaesthesiology; University hospital Wuerzburg; Oberduerrbacherstr, 6; 97080 Wuerzburg, Germany.
BMC Anesthesiol. 2008 Nov 14;8:7. doi: 10.1186/1471-2253-8-7.
Although the minimization of the applied tidal volume (VT) during high-frequency oscillatory ventilation (HFOV) reduces the risk of alveolar shear stress, it can also result in insufficient CO₂-elimination with severe respiratory acidosis. We hypothesized that in a model of acute respiratory distress (ARDS) the application of high oscillatory frequencies requires the combination of HFOV with arteriovenous extracorporeal lung assist (av-ECLA) in order to maintain or reestablish normocapnia.
After induction of ARDS in eight female pigs (56.5 ± 4.4 kg), a recruitment manoeuvre was performed and intratracheal mean airway pressure (mPaw) was adjusted 3 cmH₂O above the lower inflection point (Plow) of the pressure-volume curve. All animals were ventilated with oscillatory frequencies ranging from 3-15 Hz. The pressure amplitude was fixed at 60 cmH₂O. At each frequency gas exchange and hemodynamic measurements were obtained with a clamped and de-clamped av-ECLA. Whenever the av-ECLA was de-clamped, the oxygen sweep gas flow through the membrane lung was adjusted aiming at normocapnia.
Lung recruitment and adjustment of the mPaw above Plow resulted in a significant improvement of oxygenation (p < 0.05). Compared to lung injury, oxygenation remained significantly improved with rising frequencies (p < 0.05). Normocapnia during HFOV was only maintained with the addition of av-ECLA during frequencies of 9 Hz and above.
In this animal model of ARDS, maximization of oscillatory frequencies with subsequent minimization of VT leads to hypercapnia that can only be reversed by adding av-ECLA. When combined with a recruitment strategy, these high frequencies do not impair oxygenation.
虽然高频振荡通气（HFOV）时应用的潮气量（VT）最小化可降低肺泡剪切力的风险，但这也可能导致严重呼吸性酸中毒时 CO₂ 清除不足。我们假设，在急性呼吸窘迫综合征（ARDS）模型中，高频振荡频率的应用需要将 HFOV 与动静脉体外肺辅助（av-ECLA）相结合，以维持或重新建立正常碳酸血症。
在 8 头雌性猪（56.5 ± 4.4 kg）中诱导 ARDS 后，进行募集操作，将气管内平均气道压（mPaw）调整至压力-容积曲线下拐点（Plow）以上 3 cmH₂O。所有动物均以 3-15 Hz 的振荡频率进行通气。压力幅度固定在 60 cmH₂O。在每个频率下，使用夹闭和去夹闭 av-ECLA 进行气体交换和血液动力学测量。每当去夹闭 av-ECLA 时，都会调整通过膜肺的氧气吹扫气体流量，以实现正常碳酸血症。
肺募集和 Plow 以上 mPaw 的调整导致氧合显著改善（p < 0.05）。与肺损伤相比，随着频率的升高，氧合仍显著改善（p < 0.05）。仅在频率为 9 Hz 及以上时添加 av-ECLA，才能维持 HFOV 期间的正常碳酸血症。
在这种 ARDS 动物模型中，最大程度地增加振荡频率，随后最小化 VT，导致高碳酸血症，只有通过添加 av-ECLA 才能逆转。当与募集策略结合使用时，这些高频不会损害氧合。
