ECMO is the last treatment option for critically ill patients suffering from respiratory and circulatory failure or even cardiac arrest[8]. Air embolism in the ECMO circuit is a lethal and iatrogenic complication. Several factors contribute to gas entering the ECMO circuit, which is listed as follows: 1) gas accidentally transits from deep veins to ECMO pipelines during venipuncture. 2) Gas enters into the side hole due to the pressure difference when adjusting or withdrawing the side hole because the ECMO venous line takes off, leading to severe gas embolism. 3) gas enters the oxygenator. There are three channels for air, blood, and water in the oxygenator. The oxygenator is under positive pressure when the pump works and under negative pressure when the pump temporarily runs, which may allow gas to enter the membrane for a prolonged period; or 4) the extension of continuous renal replacement therapy(CRRT) pipelines, including many joints and tees, increases the possibility of gas entering pipelines when patients are treated with ECMO in combination with CRRT (Fig. 2).
We present the case of air bubbles appearing in the pipelines during ECMO therapy. In this case, gas that has quickly dissolved in the blood turns into bubbles, which is different from gas entering the pipelines. Insufficient venous return is caused by cardiac arrest and trauma (hypovolemia), whereas high pump speed relative to inflow resistance and blood volume results in excessively negative drainage pressure. When the ECMO flow rate was not smooth, negative pressure formed at the venous line of the ECMO machine. The reason may be due to a contradiction between insufficient venous return and excessively negative drainage pressure. This occurrence is similar to that of decompression sickness[7]. Air bubbles rarely occur in the ECMO circuit when it is well sealed. When the pump speed and blood flow are extremely mismatched, it is vital for us to pay attention to ECMO decompression illness caused by drainage insufficiency[9]. Air intake in this pipeline is different from the above four conditions. In either case, gas entering ECMO pipelines is lethal. With effective management, air in the circuit could be avoided during ECMO therapy. If this happens, we need to immediately clip the ECMO loop and check the reasons. Circuit change or deairing using the backflush technique could be used to re-establish ECMO flow[6]. Air in circuits leads to deleterious consequences, such as cerebral air embolism[5]. Decompression illness during extracorporeal membrane oxygenation should never be overemphasized, especially during special procedures.