Anesth Analg 2001;92:338-340
© 2001 International Anesthesia Research Society
CARDIOVASCULAR ANESTHESIA
Transesophageal Echocardiographic Imaging of a New Aortic Cannula for Differential Perfusion During Cardiopulmonary Bypass
Kent H. Rehfeldt, MD, and
David J. Cook, MD
Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
Address correspondence and reprint requests to Kent H. Rehfeldt, MD, Department of Anesthesiology, Mayo Clinic and Foundation, 200 First St. SW, Rochester, MN 55905. Address e-mail to rehfeldt.kent{at}mayo.edu
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Abstract
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Implications: We describe the use of echocardiographic imaging to assist in the placement of an aortic cannula that provides differential perfusion of the arch and descending aorta during cardiac surgery in adults.
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Introduction
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The optimal temperature for cardiopulmonary bypass (CPB) remains indeterminate. Advantages of warm CPB may include improved postbypass cardiac index (1), decreased use of autologous blood products (1,2), and an increased rate of spontaneous defibrillation after CPB (3). However, concern about neurological outcomes with warm CPB techniques (4) has kept the issue of temperature management during CPB controversial. To simultaneously achieve the benefits of systemic normothermia and cerebral hypothermia, a number of strategies, such as topical cooling and antegrade or retrograde perfusion, have been used (5). Most recently, a triple-lumen, balloon-tipped, endovascular aortic cannula (CNPB, CardeoNeural Pulmonary Bypass SystemTM; Cardeon Inc, Cupertino, CA) has been developed that can achieve simultaneous cerebral hypothermia and systemic normothermia in a large animal bypass model (6). This device is a polyurethane 24F, three-lumen, coaxial cannula with a distal aortic balloon. The central lumen delivers blood to the descending aorta, has a single end port, and passes through the center of the balloon. Proximal to the balloon is the outer lumen with multiple side holes, allowing for perfusion of the arch. The third lumen allows for inflation and deflation of the balloon that separates proximal and distal perfusion ports. Transesophageal echocardiography (TEE) confirmed cannula positioning in the initial animal studies (6), and we now report on the use of TEE to guide the placement of this device in its first clinical application.
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Methods
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The CNPB cannula is inserted through a standard ascending aortic aortotomy and advanced until the deflated balloon resides distal to the origin of the left subclavian artery. In this position, balloon inflation allows for segmentation of the aortic arch and descending aorta ( Fig. 1). A section of bifurcated tubing distal to the oxygenator allows partial diversion of flow through a second heat exchanger in the bypass circuit and ultimately into the proximal (aortic arch) lumen of the cannula.
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Figure 1. Schematic of the CardeoNeural Pulmonary Bypass SystemTM differential aortic perfusion cannula. The balloon is inflated distal to the left subclavian artery to allow segmentation of the aortic arch from the descending aorta.
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To image the proximal descending aorta and correctly positioned cannula, the descending aorta is first located by obtaining a four-chamber view and rotating the TEE probe counterclockwise 90°–120°. With this transverse view of the descending aorta, the probe is slowly withdrawn and the aorta inspected. As the probe tip nears the subclavian artery orifice, some clockwise rotation and anteroflexion is often necessary to maintain a view of the aorta. Once the cannula is inserted, switching to a longitudinal or near-longitudinal (90°–120°) imaging plane allows for a long-axis view of the device. Returning to the transverse view of the aorta and inflated balloon is, however, most helpful in assessing aortic diameter and degree of balloon occlusion.
TEE facilitates several aspects of cannula deployment. First, before insertion, both the ascending and descending portions of the aorta are examined, and the grade (I–IV) of atheromatous change is determined. Although several grading scales for aortic atheromatous disease have been proposed, we have used the four-point scale proposed by Davila-Roman et al. (7). Second, the diameter of the proximal descending aorta 3–5 cm distal to the left subclavian artery orifice is measured in a transverse plane. This diameter is then used to calculate the inflation volume required to achieve 90% occlusion of the descending aorta. The inflation volume is based on a nomogram provided by the manufacturer that relates aortic cross-sectional area to maximal balloon cross-sectional area at various inflation volumes. Subtotal occlusion of the aorta isolates the cannula’s proximal and distal perfusion ports and, therefore, arch and descending aortic circulations. Subtotal occlusion also reduces the likelihood of injury to the aortic intima. Third, continuous TEE monitoring during placement ensures positioning of the cannula such that the balloon lies distal to the orifice of the left subclavian artery. Fourth, by measuring the maximum short-axis diameter of the inflated balloon and aorta at the same level, the ratio of the two areas and hence the percentage of aortic occlusion by the balloon can be obtained. Last, the proximal descending aorta can be inspected after decannulation to exclude aortic injury.
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Results
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After IRB approval, the first clinical application of the cannula was in a 46-yr-old man with severe aortic insufficiency requiring valve replacement. Intraoperative TEE was performed with an Acuson 128XP® (Acuson Corp, Mountain View, CA) ultrasound machine and a biplane probe. Imaging before aortic cannulation excluded significant atheromatous disease in both the ascending and descending aorta, and the diameter of the descending thoracic aorta was mea-sured in the transverse plane. Continuous TEE imaging during aortic cannulation confirmed correct placement of the cannula such that the balloon was distal to the orifice of the left subclavian artery. After application of the aortic cross-clamp, the balloon was inflated with indocyanine green (ICG) dye. Subtotal occlusion of the aorta was confirmed by demonstrating blood flow around the balloon by color flow Doppler interrogation, and the degree of occlusion was calculated by measurements of the balloon and aortic diameter at the region of maximal balloon diameter.
The second patient in whom the CNPB cannula was used was a 61-yr-old man with severe aortic valvular insufficiency necessitating valve replacement. An Acuson Sequoia® (Acuson Corp, Mountain View, CA) ultrasound machine with a multiplane probe was used for intraoperative TEE. As in the first patient, imaging of the ascending and descending aorta before cannulation excluded the presence of significant atheromatous disease. Similarly, the diameter of the descending aorta was measured, and the volume required for balloon inflation was determined. After aortotomy, cannula position and balloon position were confirmed with continuous TEE imaging. Because the cannula and deflated balloon were easily visualized ( Fig. 2), we felt that ICG dye might not be necessary for adequate echocardiographic imaging of the inflated balloon. Therefore, the balloon was filled with saline ( Fig. 3), and imaging was equivalent to that when ICG dye was used. A short-axis view of the proximal descending aorta at the level of the inflated balloon allowed for determination of the cross-sectional area of the balloon, the aorta, and degree of aortic occlusion.
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Figure 2. Transesophageal echocardiographic image at 123° of the proximal descending aorta. The distal orifice (arrow) of the differential aortic perfusion cannula directs flow caudally in the descending aorta. The deflated balloon (arrowheads) is easily visualized.
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Figure 3. Longitudinal transesophageal echocardiographic view (91°) of the proximal descending aorta. The distal orifice (arrow) of the differential aortic perfusion cannula directs flow caudally in the descending aorta. The balloon (arrowheads) is inflated with saline.
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We have used differential perfusion with the CNPB device in 12 patients at our institution. In each case, TEE has proven invaluable in assessing the aorta before cannulation, in determining correct device placement, and in ensuring subtotal aortic occlusion by the inflated balloon. Both biplane and multiplane TEE probes have been used successfully. No patient has been excluded from the study on the basis of severe aortic atheromatous disease. As a result of our experience with the second patient, we have used saline to inflate the cannula balloon in all subsequent patients and have encountered no difficulties in imaging. On the basis of TEE evaluation after inflation, the amount of saline in the balloon has either been increased or decreased to achieve subtotal (near 90%) aortic occlusion. Furthermore, no aortic trauma has been identified in any patient in whom the CNPB device has been used.
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Discussion
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The use of TEE in guiding placement of endoaortic devices has been previously described. Nishioka et al. (8) reported their experience in TEE-guided deployment of intraaortic balloon pumps (IABP) in the operating room. Many of the same concerns relevant to the placement of an IABP also pertain to the placement of the CNPB cannula, such as the potential for embolization of aortic atheromatous debris, occlusion of the left subclavian artery by the balloon, and aortic intimal injury. In patients undergoing IABP placement and in our 12 patients undergoing CPB with the CNPB system, TEE has been able to exclude the presence of such complications. Furthermore, in all cases, TEE has confidently identified correct placement of the intravascular device, thus eliminating the need to rely on approximate or empiric measurements to guide deployment.
We have used a number of different imaging techniques to evaluate the optimal deployment of the differential perfusion cannula. Additionally, a variety of ultrasound instruments have been used for intraoperative imaging. We have found both biplane and multiplane TEE probes to be useful in visualizing the device. Color flow Doppler interrogation of the cannula after balloon inflation, particularly when viewing the aorta in short-axis, has been valuable in ensuring subtotal aortic occlusion as demonstrated by color flow around the balloon at the area of maximum balloon dimension.
Animal data indicate that the differential perfusion cannula can effectively and rapidly achieve a temperature differential between the aortic arch vessels and the descending aorta (6). As the debate over temperature regulation during CPB continues, the use of devices such as the CNPB system may become increasingly common. In addition to its other benefits in the cardiac surgical operating room, TEE has proven to be extremely valuable in guiding the placement of intravascular devices as well as identifying or eliminating possible complications related to their use. Therefore, intraoperative TEE should be considered when the use of such devices is anticipated.
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References
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Tonz M, Mihaljevic T, von Segesser LK, et al. Normothermia versus hypothermia during cardiopulmonary bypass: a randomized, controlled trial. Ann Thorac Surg 1995; 59: 137–43.[Abstract/Free Full Text]
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Boldt J, Knothe C, Zickmann B, et al. Platelet function in cardiac surgery: influence of temperature and aprotinin. Ann Thorac Surg 1993; 55: 652–8.[Abstract]
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Lytle BW, McCarthy PM, Meaney KM, et al. Systemic hypothermia and circulatory arrest combined with arterial perfusion of the superior vena cava: effective intraoperative cerebral protection. J Thorac Cardiovasc Surg 1995; 109: 738–43.[Abstract/Free Full Text]
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Boston US, Sungurtekin H, McGregor C, et al. Differential perfusion: a new technique for isolated brain cooling during cardiopulmonary bypass. Ann Thorac Surg 2000; 69: 1346–50.[Abstract/Free Full Text]
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Davila-Roman VG, Phillips KJ, Daily BB, et al. Intraoperative transesophageal echocardiography and epiaortic ultrasound for assessment of atherosclerosis of the thoracic aorta. J Am Coll Cardiol 1996; 28: 942–7.[Abstract]
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Nishioka T, Friedman A, Cercek B, et al. Usefulness of transesophageal echocardiography for positioning the intraaortic balloon pump in the operating room. Am J Cardiol 1996; 77: 105–6.[ISI][Medline]
Accepted for publication October 17, 2000.
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Abstract
Introduction
