Up to now, the history of extracorporeal lung support has been a tale of great expectations and even greater disappointments. In 1972, Hillet al.1published the first case report on the use of extracorporeal membrane oxygenation (ECMO) in a young patient who suffered from acute respiratory distress syndrome (ARDS) after trauma. At that time, mortality rates from ARDS were extremely high and thus this report was embraced with great enthusiasm. However, only 2 yrs later reality caught up when the results of a randomised controlled trial using ECMO in ARDS were published showing mortality rates of >90% in both treatment arms2.
Despite these sobering results, several groups of investigators continued to work on extracorporeal devices. Gattinoni and co-workers3,,,,4were the first to introduce the use of extracorporeal CO2removal to support protective ventilation strategies, now with survival rates of ∼50% among patients with ARDS. However, once again a randomised controlled trial failed to show a survival benefit in ARDS patients treated with extracorporeal CO2removal5although the survival rates (33% in the extracorporeal groupversus现在,常规通风组的42%比1970年代要好得多。
The reasons for the failure to demonstrate a survival benefit with extracorporeal lung support were certainly manifold. The study by Morriset al.5included only 40 patients and was gravely underpowered (for comparison, the ARDS Network trial on low tidal volumes recruited >800 patients before a survival difference of 22% became statistically significant6)。更重要的是,在这些时代使用的技术设备没有充分开发,因此容易发生并发症,例如血栓形成,出血和感染。此外,保护性通风策略与当今使用的策略有很大不同。例如,在他们的第一批研究中,Gattinoniet al.4使用了基于低呼吸频率和高潮汐体积的通气概念。如今,这种方法不会被认为是肺部保护性6-8.
那么,为什么在现代重症监护病房中,体外设备可能比以往任何时候都更频繁?有几种解释,包括提供更好的设备的可用性,这些设备较不容易发生并更方便使用。此外,我们对体外设备的生理学有了更好的了解,并可以针对单个患者的需求定制使用。现在,常规的静脉静脉ECMO现在主要用于需要全部心肺支持的患者。严重氧合衰竭的患者是静脉内肺载体的候选者。主要伴有高含量呼吸衰竭的患者可以通过动脉抗辅助装置治疗。静脉动脉和静脉静脉的方法都需要使用泵来产生3-5 L·min的流速-1to ensure sufficient organ perfusion and oxygenation, respectively. In contrast, no pump is needed for the arterio-venous approach since low-resistance devices are available which allow sufficient blood flow driven by the patient's own blood pressure. These so-called pumpless extracorporeal lung assist (pECLA) devices achieve flow rates of 0.8–1.5 L·min-1which is sufficient to allow effective CO2removal. Vascular access is usually obtained with 13–15F arterial cannulas and 15–17F venous cannulas inserted into the femoral vessels.
The pumpless arterio-venous approach is increasingly being used in patients with ARDS, although there is still no data from randomised controlled trials to support this concept. However, the results of the ARDS Network have demonstrated that a less invasive ventilation strategy with low tidal volumes of 6 mL·kg-1and inspiratory plateau pressures of 30 cmH2O (3 kPa) resulted in a better survival rate than what was considered conventional ventilation at that time,IE。tidal volumes of 12 mL·kg-1和灵感高原压力高达50 cmh2o(5 kPa)6.Data from experimental models suggest that even lower tidal volumes and plateau pressures might be more beneficial9but in real life, protective ventilation is often limited by hypercapnia and respiratory acidosis. Although hypercapnia by itself has not been associated with adverse consequences, it may be extremely distressing for the patient, resulting in poor patient-ventilator interaction, the need for intensified analgosedation or even relaxation and an increasing use of catecholamines.
Beinet al.10have reported the largest series on the use of pECLA in 90 patients with ARDS. Although this study was noncontrolled, it confirmed the concept that pECLA can be used to ensure protective ventilation. In that study, survival rates were lower than expected but this does not prove that pECLA was responsible for improved survival. Another study demonstrated that pECLA can be used successfully to bridge patients with end-stage lung disease to transplantation11.但是,pecla的使用可能有害,因为它与显着的并发症,最重要的下肢缺血,隔室综合征和插管血栓形成有关10.
In the present issue of theEuropean Respiratory Journal,,,,Hommelet al.12report on four patients with ARDS and bronchopleural fistulas with persistent air leakage despite surgical interventions. These patients usually have a poor prognosis if they develop respiratory failure and require mechanical ventilation with high airway pressures. In all four patients, the use of pECLA corrected hypercapnia and enabled the reduction of airway pressures, and all patients were eventually discharged from the hospital. As Hommelet al.12在他们的论文中指出,没有证据表明Pecla的使用是良好结果的原因,但是有令人信服的病理生理原因支持这一假设。
未来发展的主要障碍是什么ment of extracorporeal lung assist? Many would argue that we need data from randomised controlled trials to warrant the use of such invasive, costly and potentially dangerous devices. In fact, such trials are currently underway but it will take years until results become available and the question remains as to whether these trials are adequately designed and powered to demonstrate an improved outcome. Unfortunately, those patients who might benefit the most from extracorporeal lung support may be too ill to be eligible for randomised controlled trials. Even in modern intensive care medicine many of our decisions are based on experience and pathophysiological considerations rather than on evidence from rigorous trials, and this must not necessarily be a bad thing. In the setting of intensive care medicine, randomised controlled trials often enrol heterogeneous patient populations. If those trials fail, a drug or intervention is usually considered not effective although it may still be useful in selected patients. The study by Hommelet al.12is a good example of a judicious use of an experimental device based on a sound clinical and pathophysiological rationale. Until further data become available it seems to be crucial to limit the use of such devices to well-equipped intensive care units with extensive experience in managing patients with severe ARDS. Similar to other areas in medicine, volume matters and the whole team needs substantial experience with the use of these devices to avoid the numerous pitfalls and to manage potentially dramatic complications.
体外肺辅助没有死;实际上,它似乎比以往任何时候都更加活跃。但是,目前,使用Pumpless体外肺辅助和其他体外装置应仅限于专业中心,主要是三级护理医院。如Hommel的病例系列所述,此类设备可能改善了选定的呼吸衰竭患者的管理et al.12但是,当不在适当的环境中使用时,它们也可能造成重大伤害。
利益声明
A statement of interest for M.M. Hoeper can be found atwww.www.qdcxjkg.com/misc/statement.shtml
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