Extracorporeal Membrane Oxygenation Cannulation

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CHAPTER 2 Extracorporeal Membrane Oxygenation Cannulation

Thomas Pranikoff, Michael H. Hines

Step 1: Surgical Anatomy

♦ Within the carotid sheath, the internal jugular vein is anterior and lateral and the common carotid artery is medial and posterior. The vagus nerve lies posterior and between these two structures.

♦ In the femoral triangle, below the inguinal ligament, the femoral vein lies medial to the artery. More distally, the vein moves posterior to the artery.

Step 2: Preoperative Considerations—Patient Management before Extracorporeal Life Support

♦ Patients who require extracorporeal life support (ECLS) are critically ill, and proper preparation before initiating ECLS is challenging.

♦ Adequate monitoring and nursing care are essential, and required equipment (cannulas, surgical instruments, circuit and components) and personnel (operating room and ECLS) must be available.

♦ The ability to transport the patient safely with adequate ventilation and hemodynamic support should be considered.

♦ The decision of where to cannulate the patient (e.g., in the intensive care unit [ICU], operating room [OR], emergency department) needs to be thought out carefully.

♦ Most institutions will have pre-ECLS orders that need to be initiated, including ordering blood and platelets.

♦ The patient should be anesthetized to facilitate safe cannulation, avoid anxiety and discomfort, and reduce the likelihood of air embolus. We use a combination of fentanyl and rocuronium.

♦ After the vessels have been surgically exposed or a guidewire placed for percutaneous access, the patient is anticoagulated with heparin (100 units/kg for 3 minutes) before cannulation.

Type of Support

♦ Extracorporeal support is provided in two principal ways:

Venovenous (VV) bypass, which provides excellent respiratory support

Venoarterial (VA) bypass, which provides both cardiac and respiratory support.

♦ VA bypass removes blood from the systemic venous circulation, usually from the right atrium via the right internal jugular vein, and returns the blood to the systemic arterial circulation in the aortic arch via the right common carotid artery.

♦ In VV bypass, blood is drained from the venous circulation and returned to the venous circulation either through a single double-lumen catheter in the right atrium via the jugular vein or by using two cannulas in the jugular and femoral veins.

♦ Most cases of respiratory failure can be managed with VV bypass if cardiac function is adequate. This may be difficult to determine in the typical hypoxemia patient who is on high-pressure ventilation, which depresses cardiac function.

♦ After ECLS is begun and airway pressures are decreased, cardiac output increases and inotropic support can usually be weaned. VV bypass offers several advantages over VA bypass:

The avoidance of arterial cannulation eliminates potential arterial embolization and ischemia.

VV bypass eliminates need for arterial ligation or repair,

It preserves blood flow and improves oxygenation to pulmonary circulation with beneficial vasodilatory effect.

It produces no hemodynamic effects, particularly no increase in afterload.

Cannula Considerations

♦ During ECLS it is important to use a drainage (venous) cannula with the largest lumen and shortest length possible because venous drainage is achieved only by gravity siphon.

♦ In this system, if preload is adequate, the limiting factor determining maximum flow is cannula resistance, which is directly proportional to the length and inversely proportional to the fourth power of the luminal radius. This simple relationship becomes more complicated for devices that are not uniformly shaped.

♦ Cannula size is based on the outer diameter. Identically sized cannulas may vary in inner diameter according to the wall thickness of the material used.

♦ Venous cannulas generally have both end and side holes to allow flow even if the end of the cannula is occluded.

♦ Arterial cannulas generally have only end holes to prevent arterial injury from ejected blood.

♦ The cannula should resist kinking while remaining flexible and thin-walled to offer the least resistance possible.

♦ Wire-wound cannulas (e.g., Biomedicus) are resilient to kinking, whereas the thin-walled double-lumen cannulas are more prone to kink.

♦ Vascular access for ECLS in neonates is particularly challenging because of their small vessels. The route of access depends on the method used. VA bypass is indicated when both cardiac and pulmonary support is required and in neonates if access for VV support cannot be obtained (i.e., the vein is too small to accept a 12 French cannula).

♦ For VA access, the preferred site for venous drainage is the right atrium via the right internal jugular vein. The arterial infusion is directed at the aortic arch via the right common carotid artery.

♦ For VV access, a double-lumen cannula is placed into the right atrium via the right internal jugular vein. This technique is limited by the size of the vein because the smallest double-lumen VV cannula available is 12 French. For larger children (>10 kg), single-lumen cannulas may be placed into the right internal jugular vein and left or right femoral vein.

♦ Single-lumen cannulas are available in sizes ranging from 8 French for neonates to 29 French for adult-sized patients.

♦ Double-lumen cannulas are available in various sizes: 12 to 18 French (Origen Biomedical, Inc., Austin, TX) and 31 French (Avalon Laboratories, LLC, Rancho Dominguez, CA).

Selection of Technique

♦ The VA bypass requires an open technique for arterial ligation to prevent leakage around the cannula and possible distal embolization from flow past the cannula.

♦ In infants and small children, the carotid artery is usually safe to ligate distally without major sequelae.

♦ VV bypass can be performed via a percutaneous or open technique. Although jugular vein ligation is usually tolerated, there is evidence that it may produce high venous pressure, which can lead to cerebral ischemia.

♦ Because the size of the vessel in relation to the cannula is unknown, vessel disruption is a risk when percutaneous access is used. For this reason, our preferred method is the semi-open technique. This technique requires a small incision to see the size of the vein as an aid to selecting the correct cannula size (usually 12 or 15 French in a newborn).

♦ Cannula insertion can also be viewed through this incision if desired.

♦ With this technique, vessel ligation is not used; this has several advantages: cephalad flow into the cannula increases the amount of deoxygenated blood available to enter the bypass circuit, the vessel may remain patent after decannulation (and can be recannulated if needed), and kinking of the cannula at the vessel is reduced because the vessel is not fixed to the cannula with a ligature, which can act as a fulcrum around which the cannula kinks. Also, adjustment of cannula depth is much simpler.

Step 3: Operative Steps—Cannula Insertion for Neonatal ECLS

VV/VA Cannulation: Open Technique

Preoperative

♦ Vascular cannulation and decannulation are performed in the neonatal ICU with the patient under adequate sedation and neuromuscular blockade.

♦ Neuromuscular blockade is especially important in preventing the potentially lethal complication of an air embolus during introduction of the venous cannula.

♦ Heparin sodium (100 units/kg) is drawn up for subsequent administration.

Anesthesia

♦ Local anesthesia is administered by infiltration of 1% lidocaine.

Operation

VV Cannulation: Semi-open Technique

Incision and Vein Exposure

♦ A transverse cervical incision approximately 1.5 to 2 cm long is made 2 cm above the right clavicle between the heads of the sternocleidomastoid muscle.

♦ The platysma is divided with electrocautery, and the anterior surface of the internal jugular vein is exposed with minimal dissection. The vessel is observed, and an appropriately sized VV ECMO cannula is selected.

Guidewire Placement (Fig. 2-2)

♦ The cannula skin exit position is selected so that the cannula will lie behind the right ear when the head is returned to the midline.

♦ The needle and catheter are placed through the skin 2 cm superior to the incision and into the internal jugular vein to enter either under the skin flap or just inside the incision. The needle is removed, and a 0.035-inch-diameter guidewire is advanced and the catheter withdrawn.

♦ A Teflon guiding obturator is placed over the guidewire into the vessel and right atrium. The skin exit is slightly enlarged with a scalpel.

♦ Fluoroscopy is very helpful to observe appropriate guide wire placement, as well as during dilation and cannula advancement.

Figure 2-2

Cannula Placement (Fig. 2-3)

♦ Heparin (100 units/kg) is administered and 3 minutes allowed for circulation.

♦ The selected cannula is advanced over the Teflon obturator into the vein under direct vision to confirm entrance into the vein.

♦ The arterial (red) port of the cannula must be directed anteriorly to allow the arterial blood to cross the tricuspid valve and minimize recirculation of circuit blood.

♦ The tip of the cannula is placed 6 to 8 cm from the skin.

Figure 2-3

Wound Closure and Cannula Fixation

♦ The relatively low venous pressure allows adequate hemostasis around the venotomy site without any ligature. This prevents kinking of the thin-walled cannula, which often occurs at the area of a ligature if it is used around the vessel.

♦ Repositioning of the cannula requires only removing the skin sutures, repositioning the cannula, and replacing skin sutures.

♦ The cannula is fixed to the skin with several 2-0 silk sutures. The incision is closed using a monofilament suture.

Decannulation

♦ After respiratory failure has resolved to allow ventilation without extracorporeal support, decannulation can be performed by removing the skin sutures, pulling the venous cannula, and holding pressure on the catheter exit site for 5 minutes or until bleeding stops.

♦ Care must be taken to remove the entire cannula rapidly to prevent air from entering the side holes while the end of the cannula remains in the vessel.

Cannula Insertion for Pediatric ECLS

♦ Children older than infants have different bypass needs, similar to those of adults. Vessels are larger and make more options available for access.

♦ VV bypass is still used preferentially for respiratory support. VA bypass is preferred for cardiac support, including postoperative patients who do not wean from cardiopulmonary bypass after heart surgery.

♦ Children who are not yet old enough to walk have very small femoral vessels that are unsuitable for use in bypass access. For this reason, in this group (weight less than 10 kg), a double-lumen cannula in the jugular vein for VV bypass or single cannulas in the jugular vein and carotid artery must be used for VA bypass.

♦ Occasionally a small child with respiratory failure has a jugular vein that is too small to allow a large enough double-lumen cannula for adequate flow on VV bypass and must be placed on VA bypass.

Venovenous Bypass

♦ As described, VV bypass in small children can be achieved using a double-lumen cannula either placed by a modified Seldinger technique, as described already, or entirely percutaneously if the vein is judged to be adequate to receive the cannula.

♦ Children who weigh more than 10 kg usually have large enough veins to use a two-cannula technique by placing cannulas in both the femoral and jugular veins.

♦ The selection of cannulas is again based on two criteria: (1) the largest cannula that the vein will accept based on judgment and (2) a large enough drainage cannula to allow for enough flow (100 mL/kg/min), which can be estimated by the M number provided by the manufacturer.

♦ The issue of which cannula to use for drainage and reinfusion has two options. The jugular vein cannula will often allow more drainage. If the end of this cannula is in the atrium and preload is adequate, it can drain until the atrium collapses around the cannula and the pump flow is interrupted by servoregulation. Flow is thought to be greater in this situation because the atrium is spherical compared with the cylindrical shape of the femoral or iliac vein. However, if pump blood is reinfused into the femoral vein cannula, recirculation is often significant. This may be due to the direction of blood draining into the right atrium from the inferior vena cava being directed preferentially into the jugular cannula before mixing occurs.

♦ Rich and colleagues showed that draining blood from the femoral cannula and reinfusing into the jugular cannula result in higher arterial saturation (i.e., oxygen delivery), even though the total flow achievable is less because recirculation is minimal.

♦ We prefer this method of bypass and try to use a femoral cannula that reaches the intrahepatic vena cava, which is large and does not collapse.

Venoarterial Bypass

♦ For cardiac failure, most pediatric patients are cannulated through the neck using the jugular vein and carotid artery by cutdown.

♦ Patients placed on bypass after cardiac surgery may use their cannulation sites in the chest that are used for cardiopulmonary bypass.

Cannula Insertion for Adolescent ECLS

Venovenous Bypass

♦ Cannulation for adolescent VV bypass uses two cannulas placed in the jugular and femoral veins. These cannulas can be placed safely by a percutaneous method. A large cannula (23 to 29 French) should be placed for drainage and a somewhat smaller cannula (21 to 23 French) for venous reinfusion.

♦ It is especially important for the drainage cannula to have side holes in addition to an end hole to maximize flow and allow flow to continue if the end becomes obstructed.

♦ An adult-sized double-lumen cannula has been introduced by Avalon Laboratories and is available in sizes up to 31 French, which is suitable for most adult patients, even those who are obese.

♦ Recirculation is a problem that can be solved as described in the preceding section on pediatric cannulation.

Venoarterial Bypass

♦ In adolescents VA bypass can be achieved using many different cannulation schemes.

Jugular vein to carotid artery bypass as used in infants has been used successfully and works well, especially for combined cardiac and pulmonary support. It provides very good perfusion to all branches of the aortic arch and distal aorta, but it increases afterload by increasing aortic pressure. Ligation of the cerebral artery may cause cerebral edema.

Jugular vein to femoral artery bypass provides adequate distal perfusion, but this approach can fail to perfuse the aortic arch in situations where the native cardiac function is good. If the blood ejected from the left ventricle is desaturated because of pulmonary dysfunction, the aortic arch might not receive well-oxygenated pump blood, and the result will be hypoxemia in the upper half of the body. This problem can be solved by adding an additional perfusion cannula to the venous circulation to create venoarteriovenous bypass, which increases oxygenation of the right ventricular blood much like VV bypass and provides the hemodynamic support of VA bypass. The increased afterload from VA bypass may prevent the failing left ventricle from ejecting blood and result in high left atrial pressure, causing pulmonary edema. This situation can be managed by draining blood from the left atrium into the venous side of the bypass circuit either from direct cannulation of the left atrium by thoracotomy or by catheter-based balloon atrial septostomy.

Arterial cannulation can be performed either percutaneously or by direct cutdown of the vessel. With either method, if the cannula is large enough to diminish flow, distal ischemia may result. Several methods of managing this type of ischemia have been described.

Placement of a distal perfusion catheter can be used with the open technique by placing a connector with a side port and placing small tubing directed into the vessel distally at the cutdown site. With the percutaneous technique, an arterial line can be placed into either the dorsalis pedis or posterior tibial artery by cutdown and the distal pressure measured. If the pressure is less than 50 mm Hg, the catheter can be perfused by a line from the perfusion limb of the circuit.

♦ Decannulation can be performed similarly to previously described methods for the vein (direct pressure for percutaneously placed line, ligation of the jugular vein for cutdown placement).

Arterial decannulation is more complicated. Direct pressure may be all that is needed for percutaneously placed arterial cannulas. The larger the cannula is in relation to the artery, the more likely that a pseudoaneurysm or arterial stenosis will result.

An alternative to this method is venous patch angioplasty, a technique used for removing arterial cannulas placed by cutdown. In this technique, the vessel is controlled by a clamp, and the cannula is removed. A diamond-shaped patch of vein is then sutured into the defect, which both closes the hole and prevents stricture at the repair site.

Transthoracic Cannulation

♦ In certain circumstances, cervical or femoral access for VA extracorporeal support is either not possible or not practical, particularly when treating patients who have not been weaned from cardiopulmonary bypass or who have undergone post-sternotomy resuscitation. In these circumstances direct cannulation of the arterial and venous system is performed using techniques and cannulas that are standardly used with cardiopulmonary bypass.

♦ Pursestring sutures of some sort are placed in the ascending aorta, usually directly in the right atrium, and brought through snares that allow the suture to be tightened around the cannula and secured, preventing leaking of blood around the cannula, and, in the case of the venous side, preventing entraining of air into the system.

♦ While in the operating room, the cannulas are usually lightly secured to the drapes or left lying on the field; it is critical to secure the cannulas in a more “permanent” fashion when providing more prolonged extracorporeal support, particularly for safety during transport. In general, this involves suturing the cannula to the chest wall at some point and then closing the wound with an artificial dressing usually made of some sort of plastic or elastic, with the cannulas exiting between the suture line between the material and the skin.

♦ If the patient becomes more lightly sedated and moves or attempts to breathe or cough, the sternal edges can separate and put tension on the cannulas, risking dislodgement. This can be prevented by either using continuous neuromuscular blockade or by using one or two heavy sutures or sternal wires to bridge the distance between the sternal edges. This prevents spreading of the distance between the edges if the patient coughs or fights the endotracheal tube. We have found this to provide more than adequate stabilization of the support apparatus and prefer it over neuromuscular blockade with their potential sequelae.

Step 4: Postoperative Care

♦ It is critical that the cannulas are well secured to the patient’s skin as well as to the bed so that tension does not pull on the cannula. Failure to adequately secure the cannula may cause malpositioning or inadvertent decannulation.

♦ The wound should be dressed with a dry, sterile dressing.

Step 5: Pearls and Pitfalls

♦ Cannulation of patients for ECMO can be quite challenging, and problems are frequently encountered. By adequately preparing the patient, complications can usually be avoided.

♦ Proper training and support of the surgeon performing these procedures will allow most of these problems to be managed without poor outcomes.

Difficulty Threading the Venous Cannula

♦ This type of difficulty can occur because the vein is too small, the catheter is too large, or there is a left-sided superior vena cava without an innominate vein.

♦ The clavicle or first rib can sometimes obstruct if the patient’s head is hyperextended or hyperrotated.

♦ Try to reposition the head. Also, severe mediastinal shift may be present with diaphragmatic hernia or pneumothorax or effusion.

Vein Division

♦ Especially in small newborns, it may be difficult to introduce the venous cannula. During attempts to do this, the vein may become divided, which will make further attempts to introduce the cannula more difficult.

♦ Vascular control is the primary goal, which is best done using a vascular clamp.

♦ Once vascular control has been achieved, placing a guidewire may be helpful to introduce the cannula.

♦ Placing stay sutures to provide traction during cannula placement will help.

♦ A ligature should be placed around the vein to tie in the cannula.

♦ At decannulation, a pursestring suture may be used to control bleeding.

Proximal Vein Lost in Mediastinum

♦ During a difficult venous cannulation, when the cannula does not thread easily, sudden loss of resistance may be due to division of the vein, which may invert into the mediastinum.

♦ Bleeding can be controlled by using direct pressure with a finger. If the vein end can be retrieved with a forceps, cannulation may be performed as above with vein division.

♦ Otherwise, if no other suitable vein is available for access, median sternotomy and access via a thoracic approach may be needed.

♦ If other access is available, control can almost always be achieved by suturing fascia to cover the hole where the vein was lost and applying direct pressure.

No Flow After Catheter Placement

♦ If there is no flow after placement of the cannula, the cannula and circuit tubing should be examined for kinking.

♦ Chest radiography or fluoroscopy should be used to assess the position of the venous cannula and reposition or replace as needed.

Intrathoracic Vein Perforation

♦ Sudden cessation of flow with hemodynamic instability is of concern for intrathoracic vessel perforation. This situation requires immediate median sternotomy and vascular repair, with subsequent open cannulation.

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