DISCUSSION
An important consideration of VV-ECMO cannulation is the minimization of recirculation. Dual-site VV-ECMO, the femoral to internal jugular VV-ECMO configuration is usually used in many centers.1-3 Recirculation refers to the reintroduction of oxygenated blood to the drainage cannula without passing through the systemic circulation, and reduces the efficiency of oxygenation by VV-ECMO. Various factors influence recirculation, such as cannulation configuration, cannula positioning, pump speed, extracorporeal blood flow, cannula size, cardiac function, intrathoracic and intraabdominal pressures, and direction of returned blood flow. In a previous study, it was recommended that the use of a multistage cannula and cannula position adjustment be used to minimize recirculation.5 The author demonstrated that the location of the most proximal holes of a multistage cannula drain a larger fraction deoxygenated blood from the upper body and less from the RA junction. Fifteen centimeter between the two cannulae is recommended to decrease recirculation, but if the drainage cannula is positioned at a lower level of RA for maintaining this distance, the ECMO flow disturbance could occur due to chattering. Single-site VV ECMO using a bicaval dual lumen cannula has recently been reported to reduce recirculation as compared with dual site cannulation.6However, due to the high cost, single-site VV ECMO could not always be available.
The cannulae position used in the present study have the benefits that deoxygenated blood from upper and lower body are effectively drained, and that VV-ECMO flow disturbance due to chattering can be prevented. Using the described technique, we were able to reduce recirculation by adjusting the position of the return cannula by the ELSA monitor, which measures the amount of recirculation using the ultrasound dilution technique. The cannula repositioning procedure described has an effect similar to a single dual-lumen bicaval cannula but does not impose a cost burden, and complication related to the procedure, such as hemopericardium (Fig. 3).7
A similar cannula position, called the X-configuration, was reported to reduce the blood recirculation fraction, significantly. However, this configuration has weaknesses that could be used after modifying return cannula by self, and might result in tricuspid valve injury or tricuspid regurgitation if the cannula were positioned through the tricuspid valve.8 Hori D. et al introduced that the double venous drainage system, which is jugular and femoral veinous drainage, provided better oxygenation than femoral venous drainage alone system.9 This system could supply sufficient venous drainage from both SVC and IVC, but there are complications, such as vessel injury, bleeding and infection related to an additional cannula. In addition, the patient’s management becomes more difficult.
This alternative position has a number of limitations. First, it could increase the risk of cannula-related infection. Cannula sites in our center were kept sealed with antimicrobial iodophor-impregnated incision drapes (3M Ioban; 3M Health Care, St. Paul, Minn). The cannula-related infection has not occurred in our ECMO cases when the sealed dressing of cannula sites was well maintained with the sterile procedure. Second, the drainage cannula could move into the RA appendage, not into SVC. The fluoroscopy-guided repositioning could be helped in this case. Last, this technique can not apply for tall patients because of the limitation of cannula length. In tall patients, inserting an additional cannula at SVC is needed for maintaining full ECMO support. However, it is able to predict that the drainage cannula could be repositioned to SVC by measuring the length between SVC and the tip of the drainage cannula in a chest x-ray.
Without cannula modification and additional cannulation, this alternative position of cannulae in VV-ECMO can provide sufficient full support in a patient even with a low intravascular volume or high intrathoracic/intraabdominal pressure. The highlight of this position technique is that position of the lowest recirculation rate has to identify using dilution ultrasound monitoring.