Peripheral VA ECMO
Femoral vessels are commonly used for canulation of a peripheral VA ECMO. Canulas can be inserted either through a surgical cut-down or percutaneously (fig. 1). In order to avoid arterial complications, it is recommended to canulate the common femoral artery rather than its bifurcation or the superficial one. It has to be reminded that the bifurcation is higher that the inguinal groove, just below the inguinal ligament. Thus, cut down, particularly if horizontal, or puncture have to be between the inguinal ligament and the inguinal groove. This notion is even more important in obese patients. Regarding canula diameter, the size of the venous one will be the limit for getting an optimal flow. For adult patients, venous canula diameter should be at least 24 French. Regarding the arterial canula, 17 to 19 French diameters will cover most of the adult patient’s requirement.
Fig. 1. Peripheral femoro-femoral veno-arterial ECMO
Surgical cut down
Horizontal incision gives better esthetic results and less infectious/lymphorea complications. However, exposition of the superficial femoral artery to insert the lower limb reperfusion catheter might be more difficult through this way. Moreover, in emergent situations like patients on cardiac massage, vertical incision might be more easy and efficient. In such a situation, the emergency is to restore outflow. We recommend only exposing the anterior aspect of the artery and the vein. In more stable situation, it is more safe (not only for implantation but also to prepare the explantation) to control proximal and distal part of both vessels with surgical loop as well as to secure the canulation site using purse string. Even the entry site for of the reperfusion catheter should be secured with a purse string. Again, if the situation allows it, it is easier to insert the reperfusion catheter before inserting the two other canulas. The guidewire is then let into the reperfusion catheter to avoid bleeding. The rest of the canulas insertion is done using Seldinger technique. Vessels can be punctured (in the middle of the purse string) directly in the operative field or through the skin in order to tunnelise the canulas. Of course, it is preferable in order to decrease infectious complication rate to avoid leaving the canulas through the surgical wound. However, more emergent is the situation, less tunnelisation will be used. Furthermore, in obese patients, direct puncture might be easier. But the guidewire can be secondary retrogradly slide through the skin in order to tunnelise the canulas. Once the guidewire is slide into a vessel, the entry point is gradually dilated and then the canula is slide on the guidewire. Surgical insertion is of course performed bedside and can be even done in remote institution by a mo- bile team [1].
Percutaneous insertion
The main difference is the puncture of the vessel. We recommend to position first the reperfusion cath- eter because it is very difficult to do it once the ou- flow canula is in place. Again, it is important to point out that puncture should be higher than the inguinal groove in order to the reach the common femoral artery. Ideally, no more than one or two attempts of puncture should be done in order to avoid hemor- rhagic complications. Echo guidance is very helpful for safe vascular puncture. Then guidewires is slide into the vessel and the orifice will be progressively dilated the same way it is done for surgical artery. Like for surgical implantation, the transcutaneous tunnel should be dilated (particularly the facia) with a for- ceps to help the sliding of the canula. The tip of the venous canula should reach the right atrium which is about 45 cm from the groin. Is is anyway better for the venous canula to be slide higher than lower since it is more easy and safe to pull on it later on rather than pushing it. The arterial canula should be introduced at the maximum. Once the canulas are on place and deaired, they are filled with saline and connected to the ECMO circuit. Lines are unclamped and pump is gradually activated to reach the appropriate outflow.
Surgical vs percutaneous implantation
There is no data in the literature randomly comparing percutaneous and surgical techniques. It is obvious that surgical implantation requires surgical tools, as well as an electro-cauteri and if possible a surgical light. It has to be done by a surgeon. In case of CPR, surgical cut-down is safer and faster. On the other hand, in stable situations, full percutaneous implantation avoids opening and might decrease the risk of infection. However, it has to point out that percutaneous method can increase the risk of vascular complication such as dissection, rupture, or event extravascular route. Thus, the choice between both methods definitely depends of the skill of the operator and the situation but it has to be emphases that conversion to surgical implantation because of percutaneous failure after multipuncturing is the worse situation.
Intrathoracic ECMO
ECMO can also be implanted intrathoracic, with canulas implanted in cardiac cavities (fig. 2). In case of post cardiotomy cardiogenic shock, it is usual in many teams to use the CBP canula to connect the ECMO circuit. It has to be pointed out that in many situations, CPB canulas do not allow to close the chest which is associated with a higher risk of bleeding. This is why we prefer to change the canulas (fig. 3). We use a 32 to 34 French angulated right atrial canula for inflow. For the outflow, we use the same canula than the one we use for femoral artery canulation, ie. a straight 19 French canula. Both canula are tunalized through the skin in order to enable chest closure and thus decreasing risk of bleeding and infection. Also, canula insertion should be performed with many cautions in order to avoid bleeding complication. Thus, purse string sutures can be reinforeced with teflon pledget. Moreover, for aortic canulation, percutaneous tools can be used allowing step by step insertion, ie. puncture of the aortic wall, slide of the guidewire, dilation of the orifice and finaly insertion of the canula. It has also to be pointed out that canulas have to be well secured. Even the ligature of the silicone tourniquet to the canula can become loos after many weeks of support. To avoid such complication, Tsui described an interesting method: before insertion, the canula is introduced into a Dacron tube which is sutured to the vascular or cardiac tissue around the insertion orifice with a running suture thus allowing to tied the Dacron graft and the canula together [2]. Due to the diameter of canulas, intra-thoracic ECMO allows an output about 1 liter higher for the same rpm, in comparison to peripheral ECMO. However, intrathoracic Ecmo does not better unload the left side cavities.
ECMO patient care
One has to understand that ECMO should be con- sidered regarding hemodynamic support what mechanical ventilation is to the respiratory support. Thus, patient care has to be the main focus but the safety and the quality of support should be regularly checked. On the other hand, this does not require a 24/7 presence of a perfusionist. Flow and rpm should be checked by the patient nurse hourly. The ECMO circuit and particularly the membrane is inspected once or twice a day by perfusionist. Particularly important is to check every day the wound and entry point dressing and to closely assess the quality of canulas attachment. Any loose attachment has to be replaced to prevent that canula slide out. If hemodynamic stability is obtain then patient should be wake up and extubation attempted. Cardiac cavities unloading as well as myocardial recovery is as- sessed with transthoracic or transoesophagal
)
Fig. 2. Аpical canulation
)
Fig. 3. Intrathoracic ECMO
echocardiography. We published that the main echocadiogra- phic predictive factor for ECMO weaning is aortic time velocity integral higher than 12 [3]. Canula withdrawal should be performed with echocardiographic assessment of cardiac function. We recommend to transitory clamp the ecmo circuit for 15 to 20 min after patient heparinization in order to assure that hemodynamic can remain stable without the ECMO support. If not, the circuit has to be exchanged and ECMO restarted.
Anticaogulation and bleeding management
After implantation, the main risk comes from bleeding. Even if the risk of bleeding is higher after surgical implantation particularly in case of intra- thoracic implantation or after cardiac surgery, and even if many of the implanted patients receive high dose of antiaggregant therapies, bleeding should not be tolerated. Thus, any attempt should be made to correct biological disorders from protamine to FFP and platelets transfusion to activated clotting fac- tors infusion. Moreover, any surgical bleeding should be corrected because in such patients, even small bleeding will not stop spontaneously. In case of ster- notomy and intractable bleeding, packing can be the solution leaving the chest open for 24 to 48 hours. Patients can be anticoagulated before canula insertion using a small dose of IV heparin (3000 to 5000 Unit). However, in most of the patients requiring ECMO implantation, coagulation is already altered due to low flow as well as to antiplatelets medication. In this situation, IV bolus of heparin might be dangerous. Thus we prefer not to give any systemic anticoagulation before ECMO implantation. After insertion, canulas are rinsed with saline to avoid clot formation during connection. Heparin is secondarily started once the patient is on support. Heparin dosage will be then adapted for aPTT around 60 seconds and according to complication. We don’t use ACT to adapt anticoagulation on ECMO.
)
Fig. 4. Рulmonary edema on ECM
If ECMO is used after cardiac CPB surgery, then procoagulant therapy should be given as usual. It has to be noted that those therapies should not be infused through ecmo port. Once the patient is on ECMO, if bleeding complication occurs, anticoagula- tion therapy can be stopped until bleeding resolves.
Unloading the left side cavities
The physiology of left ventricle overloading and genesis of pulmonary edema on ECMO is not well understood. Of course, it is well known that VA ECMO increase left ventricle afterload thus impairing ejection. However, pulmonary edema almost never occurs in patients with medication intoxication related cardiogenic even if they undergo few days of non ejecting heart. This is also quite true for patients with fulminant myocarditis. On the other hand, in patients with acute MI or even more patient with previous chronic heart failure, the rate of pulmonary edema is high even if they conserve a certain amount of left ventricular ejection. So, importance of pulmonary vein return related to the bronchial vascularisation as well as non cardiologic etiology might play a role in the genesis of pulmonary edema. Another characteristic of pulmonary edema occurring under ECMO is that diagnosis is often late on Xray since blood gas are normal despite non functioning lungs. Once Xray shows white lungs (fig. 4), then regression is very uneasy and requires aggressive therapy. Different method have been proposed in order to unload the left side cavities while on ECMO. Patients can be kept on inotropes to facilitate LV ejection. This has to be often associated to fluid removal through active diuresis or continuous filtration. In some situations, fluid removal might compromise ECMO outflow. A second easy way of preventing pulmonary edema occurrence on ECMO is to associate an intraoartic ballon pump. There are some experimental reports suggesting the benefit of such an association on decreasing left ventricular end-diastolic pressure and increasing coronary blood flow. Moreover, there are clinical reports of small non randomized series showing a better outcome of patients implanted with a IABP associated to ECMO. But, if pulmonary edema occurs, then IABP insertion does not allow curing it. Then, decompression of left side cavities is mandatory to improve the situation. Per-cutaneous method can consist in performing a in- teratrial septostomy or in implanting an impella pump through the aortic valve. Both methods are efficient. In case the heart dysfunction is mainly from the left ventricle, then insertion of a 5.0 impella can allows to wean the patient from the ECMO. Surgical techniques consist in inserting a vent canula either into the right superior pulmonary vein, the left ventricle apex or the main pulmonary artery. Although all these techniques can be performed through a mid sternotomy, pulmonary venin canulation can be done through a right thoracotomy and left apical through a left thoracotomy. The canulas are Y connected to the venous side of the ecmo. In case of left apical canulation, it is possible to set up a LVAD circuit, removing the venous canula and keeping the femoral artery canula for reinfusion or switching to a left axillary canula which is more convenient to move the patient. In our experience, systematically inserting an IAPB with VA ECMO efficiently prevent occurrence of pulmonary edema.
Conclusion
Despite the apparent easiness of implanting and using ECMO, maximal benefit will be reached if insertion procedure is well done by skilled surgeons in order to avoid occurrence of complications. The ECMO patient should then be managed by a trained medico/ surgical team to bridge the patient to either recovery, long term device insertion or cardiac transplantation.
Reference
1. Beurtheret S., Mordant P., Paoletti X. Emergency cir- culatory support in refractory cardiogenic shock patients in remote institutions: a pilot study (the cardiac-RESCUE program) // Eur. Heart J. - 2012.
2. Tsui S. International course of ECMO. - Paris, 2012. Personnal communication
3. Aissaoui N., Luyt C.E., Leprince P. et al. Predic- tors of successful extracorporeal membrane oxygenation (ECMO) weaning after assistance for refractory cardiogenic shock // Intens. Care Med. - 2011. - Vol. 37 (11). - Р. 1738-1745