Percutaneous ECMO cannulation

Preamble

Ultrasound-guided percutaneous arterial and venous peripheral ECMO cannulation by accredited staff is the default cannulation technique used at the Alfred ICU for both VA and VV ECMO commencement. This technique has led to fewer complications (in particular less bleeding) compared to open cut down techniques.

It is used for femoral vein, right internal jugular vein and femoral artery cannulation depending on the chosen ECMO configuration. Real-time vascular ultrasound and echocardiography imaging is used for access and positioning. Generally, transthoracic echocardiography is sufficient in patients with reasonable subcostal views. Trans-oesophageal echocardiography may be used only if the subcostal views are not possible and alternative assessments for positioning e.g. bedside CXR is unsatisfactory. For Dual lumen cannula (Avalon ELITEᵀᴹ) placement for VV ECMO both TOE and TTE are used.

Additional, targeted cannulation advice in the ECPR setting can be found here.

Pre-cannulation phase

Overview

Post patient selection (see each section VA, VV, ECPR for criteria) and discussion with the ECMO consultant the following pre-cannulation preparations occur at the bedside

• Patient preparation and positioning
• Bedside ultrasound sizing of vessels
• Gathering of equipment and set up at the bedside
• Allocation of roles
• Formulation of a cannulation plan (including configuration and cannula sizes)

All patients should have focused bedside echocardiography and vascular ultrasound performed (if not already done) as part of their check for suitability, to assess for any potential contraindications to cannulation e.g. aortic regurgitation (>mild) in the case of VA ECMO, severe LV dysfunction in VV ECMO and abnormal or thrombosed target vessels.

Patient preparation

The patient and/or family should receive an explanation of the procedure prior to commencement where circumstances permit. In particular, in awake patients there may be a window to brief them together at the bedside. Patient explanations should be documented including the aim of this therapy.

Patient positioning

Optimal patient positioning is important for femoral cannulation to expose the proximal part of the femoral vessels and be clear about the anatomy. Access the femoral vein above the confluence of the great saphenous vein, and the femoral artery above the bifurcation into the superficial and deep femoral arteries.

Ideally, the patient is positioned supine without any angulation at the hips. Patients in cardiogenic shock may not tolerate this and generally are more easily managed by intubation and control over their work of breathing and oxygenation before positioning and cannulation.

Note on awake ECMO cannulation

There is inter-physician variability in the practice of awake ECMO cannulation. In particular, the following should be judged before commencing awake cannulation

• Patient co-operation (and role of analgesia / local anaesthetic)
• Underlying condition e.g. severe pulmonary hypertension may mandate awake ECMO
• VV ECMO cannulation is generally not done awake due to potential for air embolism with large swings of intrathoracic pressure (patient can be intubated and then extubated post cannulation)
• Availability of medical staff to manage an airway during cannulation if required
• Ability to expose the groin with ease: a large abdominal apron may significantly impede optimal cannulation conditions, particularly if the patient requires to have the head elevated
• Presence of increased respiratory effort strongly cautions against awake ECMO due to risk of air embolism. This may be a lesser risk in cardiogenic shock with likely elevated central venous pressure
• Optimal communication with the patient to explain the process

Ultrasound assessment of target vessels

The target vessel, anatomy and the relationship with the adjacent structures are discerned. The vessel’s size is assessed by

• Ensuring that the vessel is round and the mid-line of the vessel is identified
• Measuring the inner diameter (in mm) of the target vessel in the anteroposterior dimension
• The measure in mm (!) is multiplied by a factor of 3 to determine the size of the cannula in French that can fit the vessel (1mm = 3Fr). This is more relevant for arterial cannulation. There is considerable variation in venous vessel size depending on vascular tone and filling, this is also a factor in arterial vessels
• Confirm veins are fully compressible along the accessible cannula path to rule out thrombus. Colour flow Doppler may be used to assess the artery.

Common venous cannula sizes used range from 19Fr to 25Fr. Common arterial cannula sizes range from 15 Fr to 21Fr.

Gathering equipment

Cannulation equipment is stored near bed 1 in ICU, and the primed circuit next to the ECPR trolley, which is located in the ECMO equipment area. After the equipment is gathered, the kits are opened in a sterile manner and the trolley is prepared for cannulation.

Cannulation equipment checklist

Trolley and sterile field

Defries ECMO-pack

Betadine

Four ECMO clamps

1000 ml NaCl 0.9%

10,000 units heparin

Cannulae according to formulated plan

Venous cannula – multistage for femoral access, single-stage for venous return

Arterial cannula – arterial return or jugular venous access

Ultrasound for sizing and insertion

Pajunk (ultrasound localizable) needle

Guidewire kit or guidewire with separate dilators

Dilators

Cannula fixation

Cable ties & cable tie gun

Tincture benzoin skin preps & Griplocks

ECMO console

Checked ECMO console with primed circuit

Attached heater unit

Portable oxygen

Oxygenator tubing

C clamp for the oxygenator (PLS)

Additional equipment checklist for High Flow configuration

Same as for ECMO cannulation, single arterial cannula for access

Y High flow connector

Clamps

3/8 inch Straight connector

Role allocation

Role allocation can be analogous to the ECPR role cards regarding the cannulation part. Assign a team leader (often the senior ECMO consultant), cannulator 1, cannulator 2, cannulator 3, echocardiographer, ECMO console support, and airway person if needed.

The essential task for each role

Team leader

He or she should ideally be free of any other physical task to ensure good communication between the team members, and give advice as required. It is also the team leader’s role to ensure that there is a plan for the cannulation, to anticipate potential complications, to moderate if difficulties occur and to provide feedback to cannulators and about team performance. All communication should include the team leader.

Cannulator roles

First cannulator – needle insertion, guidewire insertion, dilatation

Second cannulator – ensures that the guidewire does not get kinked or contaminated. Avoids migration of guidewire (arrhythmia risk) and withdraws the obturator before entering the right atrium.

Echo skilled operator

Provides views of IVC and aorta from subcostal position as required for guidewire confirmation. Orientation for ECMO cannula placement in RA.

ECMO console operator

Completes console and circuit check (see ECMO initiation), controls ECMO clamp, hands over circuit and runs the console.

Formulation of cannulation plan

The team leader ensures the cannulation plan is communicated to the team. Site, size and placement of the ECMO cannulae, sequence of cannulations, anticipated complications and a backup plan and resus status should be discussed. Particularly for more complex cannulations, it is useful to have every team member describe their task to everyone else to achieve maximum clarity and overview. The aim is to facilitate a smooth cannulation.

Note: Using pre-existing arterial or central venous lines in the target vessels for guidewire placement is discouraged and associated with an increased risk of infection. If patients already have a central venous line or arterial line located in the target vessels, they are to be re-sited prior to cannulation attempt. However in an emergency a re-wiring technique may be acceptable.

Cannulation phase

Ultrasound-guided vessel puncture

The sterile field is prepared with Betadine solution and the drapes applied. An ultrasound probe, covered in a sterile sheath, is used to identify the target vessels. Decide upon the optimal entry point in the vessel, focusing on the mid-point of the vessel. Both in-plane and out-of-plane techniques can be used for guidance of the procedure depending on the proceduralist’s preference. Commonly an out-of-plane technique is preferred for cannulation (except for the distal perfusion cannula). Visualisation of the tip of the needle needs to be mastered to avoid unnecessary attempts. A steady needle angle (45°) and midpoint entry into the vessel will assist in a safe dilation and cannula placement.

Note on femoral cannulation

The vessel entry point must be caudal to the inguinal ligament to prevent injury. However, it should be proximal to the inflow of the great saphenous vein to the femoral vein (risk of venous incompetence as a late complication) and proximal to the bifurcation (into superficial and deep femoral artery) of the femoral artery.

Note on internal jugular vein cannulation

If the jugular vein is used as the access line, it is advisable to puncture the vein low in the neck (e.g. two fingers above the clavicle) to allow enough distance to manipulate the tip position into the right atrium. The shorter arterial cannulae may not reach the right atrium if placed high in the neck, particularly in larger adults. This is also true for dual lumen cannulae.

Guidewire placement

After puncturing the vessel, cannulator 1 holds the needle, maintaining visualization of the puncture site to prevent needle tip migration, while cannulator 2 inserts the guidewire into the vessel. The guidewire should enter freely into the vessel and there should be no resistance while advancing the guidewire.

If resistance is encountered, remove guidewire and ensure free aspiration of blood to confirm the needle is still in the vessel. Various techniques may be trialed (including angulation, rotation, exchange to stiffer guidewire, real-time visualization of needle/guidewire with US) by an experienced operator if the guidewire can not be advanced. It is important to consider anatomical variations or obstructions which can not be overcome.

Arterial dissection and / or wall haematoma with vasospasm can also occur after vessel puncture during arterial cannulation. If there is any difficulty with advancing the guidewire check with colour flow Doppler to rule out this complication.

The best way to confirm guidewire placement is using echocardiography via the subcostal view on TTE, or via the bicaval view on TOE imaging. The J loop of the guidewire is positioned in the right atrium or the distal SVC (in the case of multi-stage cannula) for access cannula insertion. For arterial cannulation, the J loop of the guidewire is visualised in the descending aorta (if a short, 110 cm arterial guide wire is used it may not be inserted far enough to be seen in this view).

Visualisation of a single guidewire in the aorta

Visualisation of a single guidewire in the IVC

Guidewire confirmation is a crucial step before proceeding particularly in emergent cannulations to ensure the desired support modality is delivered – VA (single guidewire in IVC and aorta) vs VV (two guidewires in IVC).

Conscious monitoring of the guidewire length outside the body is also important to prevent guidewire migration out of the body (potential loss of vascular access) or migration in with potential arrhythmias or vascular damage. Following guidewire confirmation, the external length of guidewire should be noted relative to landmarks and maintained by Cannulator 2.

Vessel dilation

Once the guidewire is placed and the position is confirmed as arterial or venous, standard dilators are used to dilate over the guidewire. Cannulator 1 dilates over the guidewire. In parallel, cannulator 2 helps in preventing kinking of the guidewire by ensuring the play of the guidewire is kept intact by constantly advancing / retreating the guidewire (2-5cm). This is very important in the process of cannulation and prevents malposition of the cannula and creation of false tracks/ ruptured vessel walls. Communication between the cannulators is crucial, with immediate cessation of forward motion of the dilator if cannulator 2 indicates difficulties with the guidewire “play”.

Under-dilation (cannula size minus 1 Fr size) is the routine practice that provides a tight seal at the skin and vessel level. Over-dilation by using a dilator which is one French size bigger than the cannula can be used if difficulties are encountered during the cannula insertion stage; however, this is not usually required. Use of a scalpel is avoided altogether.

If difficulties with the dilation process are encountered, exchange to an extra stiff Amplatz wire through a smaller size fully inserted dilator can be considered. Caution should still be exercised in advancing this stiffer guidewire. The safest approach to placing a stiff guidewire without real-time radiological guidance is to limit the insertion distance to the dilator or introducing catheter distance. i.e. not introducing the guidewire beyond the introducing catheter or dilator.

Cannula placement

The cannula is fed over the guidewire in the same fashion as the dilators, with the same technique as the dilator insertion (guidewire “play” must be maintained). In addition, it is advisable to keep the cannula straight in line with the insertion path, and vital to maintain a fully inserted obturator within the ECMO cannula. Once all catheter side-holes are well within the vessel, the obturator needs to be withdrawn for venous cannulation before reaching the right atrium to avoid injury. The venous cannula can then be advanced under ultrasound visualisation. Guidewire and obturator are fully withdrawn, the cannula clamped and flushed 3 times with a tightly sealing bladder syringe, with 50 ml normal saline (generally from a solution of 1L normal saline to which 10,000 units of heparin has been added).

Cannula positioning

Cannula position in the venous system is optimised under ultrasound guidance where possible. Small corrections may also be made according to ECMO blood flow and position on CXR while maintaining sterility of the cannulation field.

VV ECMO

Venous access

Ultrasound-guided placement into the high RA or SVC. Using a multistage cannula, it is important to note that most blood enters the cannula via the most proximal (first) hole. It is essential that this portion of the cannula is sited as close to the cavo-atrial junction as possible. As a result, the tip of the multistage cannula will be beyond the RA when optimally placed (see below).

Marked reductions to PEEP following ECMO placement may result in a lower (suboptimal) cannula position after cannulation due to relative lung deflation. It is preferred and safe to place the cannula relatively high rather than too low initially.

Venous return

The single-stage return cannula is guided into the right atrium generally with a separation between access (proximal, active draining holes of the access cannula) and return cannula of at least 5 cm beyond the proximal hole of the multistage cannula to prevent clinically significant recirculation in the circuit (see image below). This refers to the radio-opaque part of the venous return cannula. There is an additional 4 cm length of a perforated tip that is not visible on the X-ray.

The tip of the multistage access cannula is positioned at the RA/SVC junction whereas the return cannula is placed more than 5cm above the proximal drainage hole.

VA ECMO

Venous access

Typically multistage access via the femoral vein is guided into the SVC (if possible) to facilitate proximal catheter drainage across the right atrium.

Arterial return

The arterial cannula is inserted to full length (most cannulae have 15 -18 cm insertable length, we do not use 23 cm for arterial return). However, if there is significant resistance to blood flow i.e. a significant elevation in post-oxygenator pressure and low blood flow, X-ray of the pelvis should be ordered to delineate the arterial cannula position and course to rule out any kink in the cannula.

Post-cannulation phase

Circuit connection

The flushed access and return cannulae are connected to the access and return limbs of the primed circuit. The procedure is slightly different in PLS and HLS circuits.

PLS circuit – sterilise the end portion of the circuit with Betadine soaked gauze (this can be done by a third scrubbed assistant if available), apply clamp and cut one hand-width above. Bring the two ends into the sterile field.

HLS circuit – reach into the sterile tray, clamp circuit with provided blue clamps at marked ends. Cut ends and remove the circuit.

Be certain about matching the access cannula to access tubing (entering pump first, blue mark on tubing) and the return cannula to return tubing (coming from oxygenator, red mark on tubing).

Final checks

Mandatory checks by cannulator before connection – assistant to remind them

• Check for obvious air – tubing, oxygenator, pumphead
• Clamp on the circuit
• Oxygen connected and turned on

Perform underwater seal connection

• Check connection for air bubbles
• Cannulators: CLAMPS OFF
• Set 1500 RPM and Console operator: CLAMP OFF
• Steadily increase ECMO support (3000-4000 RPM) to achieve desired blood flow

Confirmation

• Visualise direction of blood flow from the access cannula to pump head
• Colour change across the oxygenator confirms gas delivery and function

Notes and explanation of the process

After the patient connection, all other clamps are removed by the proceduralists. The console person takes control, sets the pump speed to approximately 1500 RPM and the post oxygenator clamp is released over approximately 3 seconds as RPM is gradually increased. The correct direction of blood flow confirmed by the cannulators. Setting the RPM to 1500 is commonly required in VA ECMO to overcome the pressure in the arterial system.

Assessment of support

Before de-sterilising the ECMO field, ensure the blood flow is adequate and the cannula position is satisfactory either by further ultrasound assessment or a CXR whilst maintaining sterility.

Securing cannulae

After ECMO commencement, the cannulation sites are dried and cannulae are secured via application of semi-occlusive dressings (tegaderm). Cannulae should be secured in position using appropriate securing devices (Griplock) with prior use of skin prep for better adhesion. Cable ties should be applied at the sites where the ECMO circuit is connected to the cannulae.

Cannulae are secured with two adhesive Griplocks, both above the knee to avoid any pull with knee movement. Tubing over potential pressure points such as the patella should be avoided.

Dispose of all the disposable items into appropriate bins. Please don’t throw the ECMO clamps as they are not disposable items. They need to be cleaned and returned for sterilisation.

Determine priorities

After establishing the patient on support, it is important to pause and assess the priorities and rank them. These may be very different in individual patients but would include

• Patient sedation
• Other vascular access
• ECMO support – distal perfusion cannula in VA ECMO
• Optimisation of blood flow and fresh gas flow
• Diagnostic tests – e.g. CT
• Interventions – cath lab, interventional radiology, etc.
• Transfer to ICU if applicable

Documentation of ECMO cannulae / Electronic Medical Record

It is essential to document the cannulation and any observed complications in the patient notes. The graphic below shows the documentation in the interactive view, which should contain as a minimum

• Site, size and type of cannula
• Insertion depth and confirmation of tip placement (if relevant)
• Operators
• Complications encountered

Step 1

Go to Interactive view – lines/devices – ECMO

If ECMO does not come up in the menu (1) go to customise view (2) to turn it on (3).

Step 2

Add device line (4) and characteristics (5). Document each line separately, including distal perfusion cannula.

Step 3

Fill in details (6) starting with Activity, and finish by signing (7)