Change of configuration

Conversion to high-flow ECMO

High flow ECMO configuration may be considered in both VA and VV ECMO configurations. It involves using two different access cannulae to access blood from both the superior and inferior vena cavae (bi-caval access) to ensure a higher proportion of venous return is captured by the ECMO circuit, allowing for higher flow rates. In VV some degree of recirculation will occur and can be accepted.

Common indications

VV ECMO

• Recurrent access insufficiency (this is important to recognise, as one might be tempted to give repeated fluid boluses that ultimately lead to worse hypoxaemia)
• Hypoxaemia with a relatively low percentage of cardiac output being captured by the ECMO circuit in the setting of suboptimally positioned VV cannulae or high cardiac output

VA ECMO

• Generally, access problems in VA ECMO are due to bleeding, cardiac compression or uneven cardiac failure with severe LV failure which will NOT BE CORRECTED with additional access cannulae.
• Differential hypoxaemia with fem-fem VA ECMO may be overcome by changing access to SVC access (jug-fem VA ECMO), a high flow configuration provides an alternative or transition to a jugular single access.
• Recurrent access insufficiency, inability to desedate and neurologically assess patients where this is a priority e.g. post-ECPR.

Prerequisites / assessment

Both the internal jugular veins need to be imaged using ultrasound to ensure that there is no DVT in the contralateral IJV, to prevent any cerebral oedema from reduced venous return due to a big cannula in the right internal jugular vein after cannulation. In patients with long term indwelling catheters like Portacaths, angiography of the superior vena cava needs to be done to rule out any SVC stenosis.

The patient’s head needs to be shaved prior to cannulation as the connecting limb from the cannula to the circuit is wrapped around the patient’s head using Grip locks to prevent cannula dislodgement.

Technique

Requirements

• Two cannulators are required as per normal cannulation
• Echocardiographer to ensure that the guidewire is not going into the RV (by confirming placement in the IVC)
• Right internal jugular vein is examined with ultrasound to exclude occlusion
• 5 Clamps and 3 (or more) staff are required to complete all connections
• ECMO flow needs to be reduced during the dilatation phase to prevent any air entrainment in the circuit due to the negative pressure at the tip of the access cannula
• Optimise patient, ventilator FiO₂ is increased to 100%

Main steps

• Cannulation of jugular vein and insertion of arterial cannula
• Extension “extension high flow tubing” primed and connected
• Y-connector spliced into access limb of circuit
• Short (“arterial”) cannula is inserted into the right internal jugular vein with the standard percutaneous cannulation technique.
• The staged dilatation technique is used to dilate over the guidewire using standard dilators and the catheter is then placed using the usual white stiff plastic introducer over the guidewire. Once the cannula tip is inside the blood vessel, the introducer is withdrawn to the marker level so that the introducer is withdrawn inside the catheter, preventing accidental RA or RV perforation.
• Attention is required to meticulous technique whenever there is potential for air embolism. Advancing the cannula with the introducer withdrawn and on flushing the cannula.
• Make sure the side port is closed tightly, and the cannula fixated and should not impinge on the ear.
• Under sterile conditions the Y-connector with long extension is primed with 0.9% Sodium Chloride and the distal (long) end (without the Y-connector) is connected to the right jugular catheter with an “under-water” seal.
• The femoral access cannula – ECMO tubing junction is draped and prepared with Betadine antiseptic
• The circuit and the access cannula are clamped and the pump is stopped. An additional clamp is applied post oxygenator by the person controlling the ECMO pump – this will be the last clamp to be removed when ECMO flow is re-established.
• The access tubing is cut approximately 50 cm below the connection to the femoral cannula and a ⅜ Y- connector inserted
• The short end of the Y-connector tubing is attached to the existing access cannula (underwater seal not required)
• The “common” end of the Y-connector is connected to the access tubing draining to the pump head after all air is excluded (underwater seal required)
• All clamps are removed and ECMO flow is re-establishedVV