Dr Arthur CW Lau, Department of Intensive Care, Pamela Youde Nethersole Hospital, Hong Kong, China. 25 Jan 2010

Figure. Setup of ECMO and CRRT circuits in ICU, Pamela Youde Nethersole Eastern Hospital
Some human swine flu patients present with rapidly progressive respiratory failure. When there is relentless oxygen desaturation despite maximal ventilatory support, extracorporeal membrane oxygenation (ECMO) using a veno-venous circuit becomes a useful option to almost fully replace or support the ventilatory function of the lungs.
It could be beneficial to start ECMO early before the lungs are damaged by oxygen toxicity and mechanical ventilation, and certainly before the patient dies as a result of oxygen desaturation. Not uncommonly, these patients also have acute renal failure. Drawing blood from the ECMO cirucuit for continuous renal replacement therapy (CRRT) in a sub-circuit is a logical strategy. The following shows you how to start a veno-venous circuit for ECMO as well as a sub-circuit for CRRT.

Disclaimer: The following is a general guidance for your reference only. The procedure should only be carried out by persons experienced in its use. Individual patient requirement must be considered.

1. On the ECMO machine, check
a. no air in circuit
b. circuit has been clamped closed to pump
c. centrifugal pump not yet running
d. water bath connected and set at 37 degrees Celsius
e. air-vent of the oxygenator is released
f. 6L/min oxygen is flowing to the oxygenator

2. Prepare the groins for insertion. Our plan this time is to insert the blood removal catheter (blue mark) at the right femoral vein and the blood return catheter (red mark) at the left femoral vein. N.B. the convention of blue/red colours as venous/arterial cannula for blood removal/return is the opposite from that for CRRT. 

3. Insert the larger cannula (e.g. 23 Fr) for blood removal (blue mark) at the right femoral vein using the Seldinger technique. It is advisable to use a bigger cannula with a lot of side holes for blood removal (labelled VENOUS cannula by the manufacturer). Link to cannla information here.

Figure. Guidewire and dilators. Procedure for the insertion of the larger and smaller cannulae is the same and is shown below

4. Insert the smaller cannula (e.g. 21 Fr) for blood return (red mark) at the left femoral vein. A tightening band has to be applied to the connection because blood is under positive pressure here after the pump. It is advisable to use a cannula of smaller size with less only 2 side holes (labelled ARTERIAL cannula by the manufacturer), otherwise re-circulation of blood from the return cannula to the removal cannula will occur. N.B. Even though this is a V-V ECMO that we are setting up, we still need one VENOUS cannula for blood removal and one ARTERIAL cannula for blood return, i.e. the reference point is the human body.

5. Give systemic heparin 5000 units iv immediately after finishing insertion of the two cannulae

6. Cutting the cannulae to prepare for connection to ECMO tubings

7. Connect the blood removal cannula (blue) to ECMO

Steps: remove introducer, make sure blood is flowing out smoothly, clamp the cannula, fill up both cannula with normal saline and make sure there is no bubble, connect the ECMO tubing to the cannula while normal saline is dripping to remove air

8. Connect ECMO to the blood return cannula (red)
Procedure as for 7 above

9. Prepare CRRT v-tubing at the blood return (red) cannula by inserting a three-way stopcock.

10. Remove all clamps to start the ECMO circulation

Clamps are removed one by one and circulation starts. If blood flow is smooth and there is no significant recirculation, SpO2 should increase almost instantaneously. SpO2 of this patient began as only around 85% on 100% oxygen, and it can be seen to be increasing up to 98% when ECMO starts, and thus the oxygen supply through the ventilator can be dialed down to avoid oxygen toxicity, and pressure level or tidal volume can be further decreased to minimize baro-/volutrauma in the diseased lungs.

11. Start the CRRT sub-circuit within the ECMO circuit. Blood is drawn from the blood removal cannula (blue) near the ECMO machine and returns to the blood return cannula (red) at the three-way stopcock.

12. Start blood pump at 2000 revolutions per minute (RPM ). Adjust to achieve the desired blood flow (Liters per minute, LPM). Exact blood flow obtained depends on the mechanical patency of the blood removal (blue) cannula, which is in turned determined by the size of the cannula, vascular patency of the patient, volume status and other mechanical factors.

13. Start systemic heparin 

The ECMO is simply an extracorporeal circuit for blood oxygenation and CO2 removal. Practically speaking, it is analogous to a CRRT circuit, only that the replacement is not fluid, but oxygen and a much higher circuit flow. The most difficult part of the procedure is possibly the large size cannulae insertion. Our opinion is that for ECMO to be effective for human swine flu patients, it is intuitive to start early at the first instance when oxygen desaturation is relentless. Delaying till the lungs are damaged by oxygen toxicity and/or complicated with secondary bacterial infection may not reveal the full benefits of this treatment modality. The CRRT machine we are using has online fluid production for replacement, and thus nursing workload to look after the whole setup can be further minimized.