CHAPTER 2 Extracorporeal Membrane Oxygenation Cannulation
Step 1: Surgical Anatomy
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.
Type of 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.
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.
♦ 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).
♦ 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.
Operation
Position of Patient
♦ The patient is placed supine with the head turned to the left. A roll is placed transversely beneath the shoulders.
Exposure of the Carotid Sheath
Dissection of the Vessels
♦ The carotid sheath is opened and the internal jugular vein, common carotid artery, and vagus nerve are identified and isolated.
♦ Manipulation of the vein should be minimized to avoid inducing spasm, which makes introduction of a large venous cannula difficult.
♦ There is often a branch on the medial aspect of the internal jugular vein, and this branch must be ligated. Ligatures of 2/0 silk are placed proximally and distally around the internal jugular vein. The common carotid artery lies medial and posterior and has no branches, which makes its dissection proximally and distally safe. Ligatures of 2/0 silk are also placed around the carotid artery. The vagus nerve should be identified.
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