Extracorporeal membrane oxygenation for acute respiratory distress syndrome

Abstract

Extracorporeal membrane oxygenation (ECMO) can be a lifesaving therapy in patients with refractory severe respiratory failure or cardiac failure. Severe acute respiratory distress syndrome (ARDS) still has a high-mortality rate, but ECMO may be able to improve the outcome. Use of ECMO for respiratory failure has been increasing since 2009. Initiation of ECMO for adult ARDS should be considered when conventional therapy cannot maintain adequate oxygenation. ECMO can stabilize gas exchange and haemodynamic compromise, consequently preventing further hypoxic organ damage. ECMO is not a treatment for the underlying cause of ARDS. Because ARDS has multiple causes, the diagnosis should be investigated and treatment should be commenced during ECMO. Since ECMO is a complicated and high-risk therapy, adequate training in its performance and creation of a referring hospital network are essential. ECMO transport may be an effective method of transferring patients with severe ARDS.

Keywords: Acute respiratory distress syndrome; Extracorporeal life support; Extracorporeal membrane oxygenation; Hypoxia.

Figure 1

Vascular access and cannula position. Panel (A) shows the circulatory kinetics of VV ECMO with drainage from the right internal jugular vein (RIJV) and infusion to the femoral vein (FV). The oxygenated blood from the infusion cannula (red arrow) is mixed with the venous blood in the inferior vena cava (IVC) and right atrium (RA). The mixed blood (purple arrow) flows through the lungs to the arterial side. Panel (B) shows the circulatory kinetics of VA ECMO with drainage from the RIJV and infusion to the femoral artery. The venous blood (blue arrow) flows through the lungs to the upper body without oxygenating the blood if the lung function is poor. Panel (C) shows the correct position of the draining cannula tip for VV/VA ECMO with drainage from the RIJV and infusion to the femoral vein/artery as panels (A, B). The tip should be located in the upper or middle RA to drain blood with a lower O₂ saturation from the superior vena cava (SVC). Panel (D) shows the tip locating the lower position than panel (C), where the blood from the IVC is mostly drained. Because the blood from the IVC contains more oxygen than that from the SVC, the O₂ saturation of the drained blood becomes higher; consequently, the efficiency of oxygenation by ECMO is decreasing. A-Ao denotes ascending aorta, D-Ao descending aorta, RV right ventricle, and FA femoral artery.

Figure 2

Changes of O ₂ supplied by ECMO. Oxygen supplied by ECMO (VO₂ ECMO) is shown in an adult ARDS patient with H1N1 influenza. The amount of oxygen supplied decreases after the 30th day, indicating recovery of lung function. (Reproduced from Ref. [9]). VO₂ ECMO is calculated as follows: ECC [l/min] × 1.39 [mlO₂/gHb] × Hb [g/dl] × 10 × (outSaO₂ − inSvO₂), where ECC is extracorporeal circuit flow, outSaO₂ is the saturation of arterialized blood in the returning circuit, inSvO₂ is the venous blood saturation in the draining circuit, and Hb is the haemoglobin. The coefficient 1.39 (mlO₂/gHb) denotes the O₂ content (ml) per 1 g of haemoglobin.