Echocardiography holds a central role in the cannulation and the whole management of patients on extracorporeal membrane oxygenation (ECMO).1
Despite a limited scientific evidence, a dual-lumen cannula (DLC) seems to retain some advantages over multisite cannulation, as it can favor pronation and early mobilization on ECMO.2 Also recirculation seems reduced when correctly positioned.3 Nevertheless, a higher rate of complications, mainly because of the transatrial passage of the cannula, is reported.4,5 Therefore, experience and scrupulous technique for insertion monitoring is mandatory.
Since 2009, at our Center, all insertion procedures for ECMO cannulation have been guided and monitored by echocardiography.6
We describe how a combined transthoracic (TTE) and transesophageal (TEE) approach allows a comprehensive preimplantation assessment of biventricular functions and safely guides the procedure of insertion of a DLC.
An ultrasound venous assessment of the right internal jugular vein (patency and dimensions in relation to selected cannula size) is a prerequisite for DLC insertion. If any anatomical or pathological vein abnormality is detected, a different cannulation site (i.e., femoral-femoral) should be selected. Dual-lumen cannula insertion through the left subclavian vein has been reported,7 but this is feasible only in small size patients (because of the limited cannula length, hence not permitting a correct positioning of the inflow and outflow holes). Because its insertion is not through a straight path, it demands a stiff guidewire and a fluoroscopic visualization is recommended.
A preimplantation comprehensive echocardiographic evaluation holds great utility in further patient management. Both a TTE and a TEE evaluation should be undertaken, firstly to obtain all measurements and secondly, because the subsequent echocardiograms that will be performed in the following days are more often TTE, so baseline measurements are needed to better detect potential variations.
The preimplantation echo assessment has the following objectives:
- Evaluation of Left Venticle (LV) function, dimension and wall motion abnormalities to guide the selection between Veno-Arterial ECMO and Veno-Venous ECMO, to monitor the effects of restored oxygenation on cardiac function and changes of LV function in relation to ventilator settings and to optimize inotropic and volume therapies.
- To investigate valvulopathies and rule out the presence of endocarditis.
- Evaluation of preimplantation Right Ventricle (RV) dimensions, function, and the degree of pulmonary hypertension to be compared with post-ECMO findings. Also RV wall thickness should be considered to rule out chronic diseases.
- Search for a patent foramen ovale or any septal defect to detect a shunt as cause of hypoxia and to assess the risk of cannula migration through a septal defect.
- Assessment of volume status by evaluation of superior and inferior vena cava (SVC, IVC) dimensions and their ventilator-induced variations.
- Careful evaluation of pericardial effusion to rule out cardiac lesions correlated to the procedure.
Precannulation evaluation seems effective for risk stratifying these patients because RV dilatation, detected just before ECMO start, is an independent predictor for early mortality in severe acute respiratory distress syndrome requiring VV ECMO.8
We recommend a closed-loop communication within the team so to get a clear understanding of what maneuvers are performed and what images are displayed. As long as possible, a wide range vision of the operating field and of the echo screen should be assured for all the operators who should be contemporary capable to correlate actions, words, and images altogether.
The TEE probe should be positioned, images checked and left in place, before starting draping the patient with sterile technique.
The right internal jugular vein should be punctured under direct ultrasound visualization, by a linear probe covered with a full-length sterile sheath, in order to minimize puncture-related complications and to select the best cannulation point (larger bore of the vein, in a superficial plane, not passing through muscular structures).
Step 1: Through the Right Atrium
Gently advance the guidewire (150 cm, J-tipped, 0.36–0.8 inch, Maquet Cardiopulmonary GmbH, Rastatt, Germany) through the needle and advance it in SVC, right atrium, and direct it toward IVC. A TEE bicaval view should be obtained to clearly visualize the wire progression ((see Video 1, Supplemental Digital Content, http://links.lww.com/ASAIO/A291), which shows guidewire progression from SVC through atrium and into IVC and (see Figure 1, Supplemental Digital Content, http://links.lww.com/ASAIO/A300), depicting a TEE bicaval view with the guidewire advancing through right atrium).
The advancement of the guidewire has to be very gentle, and no resistance should be perceived during its progression. An obstacle could be caused by a jamming of the wire, and a damage of the thin wall of atrium could occur. During wire introduction, cardiac arrhythmias should prompt an immediate interruption of the procedure.
Step 2: Guidewire Advancement in Inferior Vena Cava
Gently advance further the guidewire into IVC.
In the TTE subcostal view, visualize the guidewire coming from the atrium and proceeding into IVC ((see Video 2, Supplemental Digital Content, http://links.lww.com/ASAIO/A292), which demonstrates guidewire advancing in IVC and (see Figure 2, Supplemental Digital Content, http://links.lww.com/ASAIO/A301), depicting a TTE subcostal view with the guidewire advancing into inferior vena cava). A straight (not bended) wire should be visualized continuously. Sometimes the presence of the guidewire in IVC has to be checked by moving the guide itself because it is not infrequent that artifacts mimic the presence of the wire.
The wire tip should be advanced beyond the IVC tract visible with the subcostal view to ensure an adequate firmness of the wire, provided that an excessive advancement does not cause the bending of the wire itself, because of the wedging into a distal branch.
Not rarely the guidewire can enter a sovra-hepatic vein ((see Video 3, Supplemental Digital Content, http://links.lww.com/ASAIO/A293), which demonstrates guidewire misplacement in sovra-hepatic vein). In this case, echocardiography can be helpful in detecting the wire misplacement and assist the operator in the attempts to enter the IVC. Sometimes, it is necessary to completely extract the wire and mould its terminal part in a bended shape and try to redirect the wire in IVC by rotating it.
Once the wire is visualized as properly inserted and a smooth cannula insertion can be presumed, a bolus of heparin (i.e., 30 UI/kg) can be administered, if appropriate.
Step 3: Dilators Insertion
To permit the insertion of a large bore DLC, a series of progressively larger dilators have to be subsequently introduced to dilate tissues.
As the available guidewires are long and quite cumbersome to handle and generally are not length marked, sometimes they can be inadvertently extracted during dilators withdrawn. Furthermore, quite a considerable effort is needed to dilate the tissues and the wire can be excessively pushed in. For these reasons, the position of the wire in the atrium should be continuously checked with a bicaval TEE view and viewing the wire getting out of the atrium should be promptly signaled as well as its bending ((see Video 4, Supplemental Digital Content, http://links.lww.com/ASAIO/A294), which demonstrates guidewire inadvertently extracted + guidewire bended, during dilators insertion).
Step 4: Cannula Insertion
The DLC is inserted with its dedicated tapered point spindle over the wire. The cannula progression should be as smooth as possible, but at the same time expeditious, as quite an important blood loss can occur from the drainage holes of a partially inserted cannula. A small skin incision generally can contribute to a smoother insertion. Nevertheless, the advancement of the cannula is the more dangerous part of the procedure. For this reason, the correct position of the guidewire in IVC and atrium should be rechecked before cannula insertion. In the TEE bicaval view ((see Video 5, Supplemental Digital Content, http://links.lww.com/ASAIO/A305), which demonstrates DLC insertion and (see Figure 3, Supplemental Digital Content, http://links.lww.com/ASAIO/A302), depicting a TEE bicaval view with the cannula mounted on its spindle advancing through right atrium), visualize the tip of the spindle and the cannula advancing from superior vena cava, going across the atrium and heading toward the IVC. Rapidly switch to TTE subcostal view to visualize the spindle and the cannula advancing in the IVC ((see Video 6, Supplemental Digital Content, http://links.lww.com/ASAIO/A295), which demonstrates cannula advancement in IVC and (see Figure 4, Supplemental Digital Content, http://links.lww.com/ASAIO/A303), depicting a TTE subcostal view, with the cannula mounted on its spindle advancing into inferior vena cava). Once the cannula is enough advanced in the IVC, the spindle and the wire can be removed altogether and the cannula further adjusted in its advancement.
A proper DLC position can be verified by the distance of the tip from to the atrium (according to cannula specifications and size) or directly visualizing the outflow port in right atrium ((see Video 7, Supplemental Digital Content, http://links.lww.com/ASAIO/A296), which demonstrates DLC position confirmation).
Pericardial effusion enlargement or onset must be closely monitored after cannula insertion.
Step 5: Extracorporeal Membrane Oxygenation Start
At ECMO start, the initial saline flow can be visualized from the inlet port to the atrium toward the tricuspid valve. A Doppler flow imaging from the cannula outflow can be visualized from the bicaval (TEE) or subcostal/apical views (TTE) ((see Video 8, Supplemental Digital Content, http://links.lww.com/ASAIO/A306), which demonstrates ECMO start and confirmation of correct flow from DLC).
The correct orientation of the outflow port is generally obtained placing the arterial extension above the venous one at the neck. Visualizing the flow directed toward the tricuspid valve further confirms the correct position.
Echocardiography is feasible at bedside and contributes to the safety of the procedure of DLC implantation for ECMO because it allows a complete visualization of all steps of the procedure, permits an early detection of potential complications, and assures a comprehensive preimplantation cardiac assessment.