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.