During veno-venous extracorporeal membrane oxygenation (V-V ECMO), blood is drained from the central venous circulation to be oxygenated and decarbonated by an artificial lung. It is then reinfused into the right heart and pulmonary circulation where further gas-exchange occurs. Each of these steps is characterized by a peculiar physiology that this manuscript analyses, with the aim of providing bedside tools for clinical care: we begin by describing the factors that affect the efficiency of blood drainage, such as patient and cannulae position, fluid status, cardiac output and ventilatory strategies. We then dig into the complexity of extracorporeal gas-exchange, with particular reference to the effects of extracorporeal blood-flow (ECBF), fraction of delivered oxygen (FdO2) and sweep gas-flow (SGF) on oxygenation and decarbonation. Subsequently, we focus on the reinfusion of arterialized blood into the right heart, highlighting the effects on recirculation and, more importantly, on right ventricular function. The importance and challenges of haemodynamic monitoring during V-V ECMO are also analysed. Finally, we detail the interdependence between extracorporeal circulation, native lung function and mechanical ventilation in providing adequate arterial blood gases while allowing lung rest. In the absence of evidence-based strategies to care for this particular group of patients, clinical practice is underpinned by a sound knowledge of the intricate physiology of V-V ECMO.

中文翻译：

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静脉-静脉体外膜氧合的复杂生理学：临床医生概述

在静脉-静脉体外膜氧合 (VV ECMO) 过程中，血液从中心静脉循环中排出，通过人工肺进行氧合和脱碳。然后它被重新注入右心和肺循环，在那里发生进一步的气体交换。这些步骤中的每一个都具有本手稿分析的特殊生理学特征，目的是为临床护理提供床边工具：我们首先描述影响血液引流效率的因素，例如患者和插管位置、液体状态、心输出量和通气策略。然后，我们深入研究体外气体交换的复杂性，特别是体外血流量 (ECBF)、输送氧气分数 (FdO2) 和吹扫气流 (SGF) 对氧合和脱碳的影响。随后，我们重点关注动脉血回输到右心，强调对再循环的影响，更重要的是对右心室功能的影响。还分析了 VV ECMO 期间血流动力学监测的重要性和挑战。最后，我们详细介绍了体外循环、自然肺功能和机械通气之间的相互依赖性，以提供足够的动脉血气，同时让肺部得到休息。在缺乏基于证据的策略来照顾这一特定患者群体的情况下，临床实践需要对 VV ECMO 复杂的生理学有充分的了解。