Thoracoabdominal aortic aneurysm repair with a branched graft
Art of Operative Techniques

Thoracoabdominal aortic aneurysm repair with a branched graft

Kim I. de la Cruz, Scott A. LeMaire, Scott A. Weldon, Joseph S. Coselli

Division of Cardiothoracic Surgery, Michael E. DeBakey Department of Surgery, Baylor College of Medicine; and Department of Cardiovascular Surgery, The Texas Heart Institute at St. Luke’s Episcopal Hospital, Houston, Texas, USA

Corresponding to:
Scott A. LeMaire, MD. One Baylor Plaza, BCM 390, Houston, TX 77030, USA.
Email: slemaire@bcm.edu.


Submitted Jun 30, 2012. Accepted for publication Aug 06, 2012.
DOI: 10.3978/j.issn.2225-319X.2012.08.05

Introduction

Many aspects of open thoracoabdominal aortic aneurysm (TAAA) repair are individualized according to patient-specific factors related to the type and extent of disease, comorbid conditions, and physiological reserve. One example of how surgeons can individualize the technical approach to this operation is the use of a prefabricated aortic graft with four side branches designed for reattaching the celiac axis, superior mesenteric artery (SMA), and both renal arteries (1-4). Using this branched graft in TAAA repairs is ideal when one of two conditions are met: (I) The patient has a connective tissue disorder (e.g., Marfan syndrome, Loeys-Dietz syndrome), and aortic tissue that remains after the procedure will be prone to aneurysmal dilatation, pseudoaneurysm formation, and rupture, eventually necessitating reintervention (5-7); or (II) the origins of the patient’s visceral vessels are far enough apart that an island patch reimplantation is not desirable.

The ultimate goal of these operations is to balance the need to resect and replace as much diseased aortic tissue as possible with the need to protect the spinal cord and other organs and, thereby, prevent postoperative complications. Our strategies for organ protection have been described in detail elsewhere (8-14). To protect the spinal cord, we employ mild passive hypothermia, cerebrospinal fluid (CSF) drainage, left heart bypass (LHB), sequential cross-clamping, and selective reimplantation of intercostal or lumbar arteries (9-11,14). The renal arteries are perfused with cold crystalloid solution to protect the kidneys from ischemic damage (8,12,13). Perfusing the celiac axis and the SMA with isothermic blood from the LHB circuit minimizes the duration of abdominal-organ ischemia.


Operative techniques

Preoperative planning

The patient’s history and physical examination findings are thoroughly reviewed, along with pertinent findings from the preoperative evaluation. The patient’s age, history of tobacco use, ejection fraction, pulmonary function, and kidney function, as well as the status of the carotid and coronary arteries, all factor into intraoperative decisions regarding patient management and surgical technique (10,14). The patient’s computed tomographic angiography scans are reviewed to plan various technical aspects of the procedure. The scans are checked for relevant anatomic variants, such as a retroaortic left renal vein. The diameter of the aorta in its nonaneurysmal portions—often just distal to the left subclavian for the proximal anastomotic site and at the aortic bifurcation for the distal anastomotic site—provides an idea as to the size of the Dacron graft that will be needed. Potential clamping and cannulation sites are evaluated. For example, the planned aortic cannulation site for LHB should be in a region that is free from extensive mural thrombus. The spatial relationships between the celiac, SMA, and renal arteries are assessed. When the origins of the branch arteries are substantially displaced away from one another, using a branched graft will enable their reattachment without leaving behind a large patch of aortic tissue (5). In patients with aortic dissection, the configuration of the dissecting membrane and the relationships between the true lumen, false lumen, and branch arteries are evaluated. Furthermore, areas of stenosis at the origins of the visceral and renal arteries are identified because they may need endarterectomy, stenting, or both (15). Although the final decision with regard to any of the aforementioned technical considerations is made intraoperatively on the basis of operative anatomy, it is very useful to have considered these details in advance.

To illustrate the use of a branched graft, we will describe in detail the procedure for performing a Crawford extent II TAAA repair. A typical patient undergoing an extent II repair has an aneurysm extending from the left subclavian artery down to the aortic bifurcation (Figure 1). In this particular case, there is a neck of proximal descending aorta distal to the left subclavian artery that can be clamped. Note also that the celiac axis, SMA, and right and left renal arteries are spread relatively far apart along the circumference of the aneurysmal aorta.

Figure 1
Figure 1 Preoperative anatomy: a typical patient undergoing a Crawford extent II thoracoabdominal aortic aneurysm repair will have an aneurysm extending from the left subclavian artery down to the aortic bifurcation. Note that in this case, the celiac axis, superior mesenteric artery, and right and left renal arteries are displaced away from each other, making their reattachment as a single patch undesirable

Anesthesia considerations and patient positioning

The patient is placed supine on top of a beanbag on the operating table. Both arms are placed on arm boards on either side of the table. A right radial or brachial arterial line is placed by the anesthesiologist. A large-bore peripheral intravenous line is likewise placed at this time. After intravenous sedative and muscle relaxant are administered, the patient is intubated with a double-lumen endobronchial tube for later single right-lung ventilation, and general anesthesia is induced.

The patient is placed in a right lateral decubitus position with both hips and knees flexed for spinal drain placement by the anesthesiologist. An axillary roll is placed between the bed and the patient, just under the right axilla. The spinal drain is placed at the L3-4, L4-5, or L5-S1 level. The CSF pressure is maintained at less than 10 mmHg, but the amount drained is limited to no more than 10 mL/hour. The spinal drain is secured with tape to the right side of the patient’s back, and the patient is repositioned such that the upper body is at a 60-degree angle and the hips are at a 30-degree angle to the horizontal. This allows for access to both groins in case there is a need for access to the femoral arteries. The beanbag is suction-deflated and made firm against the patient’s body to keep the patient properly positioned. The patient’s left arm is placed on top of an elevated arm board and held at an angle above the shoulders in a freestyle swimming stroke position (Figure 2). The correct position of the double-lumen endobronchial tube is confirmed with a flexible bronchoscope after final positioning. The patient’s left chest and back, abdomen, groins, and upper thighs are prepared and draped in a sterile fashion. An adhesive antimicrobial drape is placed over all exposed skin. Prophylactic broad-spectrum intravenous antibiotics are given within 1 hour of skin incision. The patient’s mean arterial pressure (MAP) is maintained in the range of 70 to 90 mmHg throughout the case.

Figure 2
Figure 2 Incision and exposure: the patient is positioned such that the upper body is at 60 degrees from horizontal and the hips are at 30 degrees from horizontal. A sigmoid-shaped skin incision is made from behind the left scapula, along the 7th rib, across the costal margin, and toward the left periumbilical region. The chest is entered through the 6th intercostal space. Left medial visceral rotation and circumferential division of the diaphragm enable exposure of the entire thoracoabdominal aorta. The use of table-mounted self-retaining retractors maintains stable exposure throughout the procedure

Incision and aortic exposure

A sigmoid-shaped skin incision is made from just posterior to the inferior aspect of the left scapula, curving along the 7th rib and across the costal margin toward a point about an inch to the left of the umbilicus. To avoid creating areas of skin necrosis, gentle curves are followed instead of sharp angles when the incision is made. When a repair will involve the iliac arteries, the incision may be extended inferiorly around the umbilicus and into the midline to just above the pubic symphysis.

The latissimus dorsi is divided, followed by the serratus anterior, to provide entry into the plane of the rib cage. Ribs may be counted downward from the apex or upward from the lower ribs to confirm appropriate interspace entry into the left pleural cavity. For most extent II thoracoabdominal repairs, the 6th intercostal space is the best entry point; the 5th intercostal space is occasionally used, such as when there is an especially large aneurysm involving the distal aortic arch and proximal descending thoracic aorta. The anesthesiologist is asked to render the left lung atelectatic at this point and to commence single right-lung ventilation. Then, the intercostal muscle is detached from the rib below the space chosen, and this incision is carried posteromedially toward the spine and anteriorly to the costal margin. The costal margin is divided, and a portion of it is resected to prevent overlap during reapproximation of the separated ribs at the end of the case. A short posterior segment of the rib may be resected to gain additional exposure.

The diaphragm is divided at the costal margin to expose the peritoneum. A fold of the peritoneum is palpated to make sure that the stomach, transverse colon, and liver are not adherent; the peritoneum is then carefully opened. The abdominal portion of the thoracoabdominal incision is then opened under direct vision to avoid inadvertent injury to intra-abdominal organs. Left medial visceral rotation is then carried out by entering the avascular plane along the line of Toldt. Retroperitoneal fibro-fatty tissues are separated from the inferior portion of the left hemidiaphragm and the anterior aspect of the left psoas muscle. Care is taken to identify and preserve the left ureter and gonadal vein. If a retroaortic left renal vein is present, it is preserved when possible; however, during extent II repairs, it is often necessary to divide the vein and later reconstruct it with an interposition graft. The left hemidiaphragm is divided circumferentially, leaving a 3- to 4-cm rim attached to the rib cage, from the left costal margin to the left crus. Retraction sutures are placed along the edge of the divided diaphragm on the cardiac side. The intra-abdominal aorta is exposed by using electrocautery to divide the retroaortic fibro-fatty tissues between the jaws of a right-angle clamp. The left renal artery and the aortic bifurcation are exposed.

A large Richardson retractor, together with an upper hand retractor, is secured to the table-mounted ether screen to hold the upper rib cage open, and a table-mounted selfretaining retractor with bladder blades pulls the lower ribs posteriorly and to the left. This provides generous exposure for the repair (Figure 2). The proximal and distal clamp sites are developed by using low-voltage electrocautery and a pair of long Metzenbaum scissors. Care is taken to identify and preserve the left recurrent laryngeal nerve and the left phrenic nerve. Sometimes, the ligamentum arteriosum must be divided to improve mobilization around the proximal descending thoracic aorta and distal transverse aortic arch. This maneuver is particularly useful when the proximal clamp site needs to be positioned on the aortic arch, between the left common carotid and left subclavian arteries. The distal clamp site is positioned at the level of the left pulmonary hilum. It is important to stay anterior to the hemiazygos vein and intercostal veins, and it may be necessary to ligate some intercostal arteries at the clamp site with medium-sized clips. Likewise, the adjacent esophagus is identified and dissected away from the aortic clamp site.

Cannulation and perfusion setup

Either the superior or the inferior left pulmonary vein can be used as an atrial cannulation site for LHB (9). The left lung is retracted posterolaterally with a moist laparotomy pad and a deep Deaver retractor. The pericardium is opened near the pulmonary veins, away from the phrenic nerve. A 3-0 pledgeted polypropylene suture is placed in the origin of the vein in a mattress fashion. At the aortic cannulation site, a purse-string suture is placed in the same manner whether the site is in the distal descending thoracic aorta or the proximal abdominal aorta (i.e., proximal to the left renal artery origin).

Heparin is administered intravenously at a dose of 1 mg/kg. A 24-French angled-tip cannula is placed in the left atrium via a pulmonary venotomy, secured with the previously placed purse-string suture and a Rummel tourniquet, and connected to the drainage line of the LHB circuit. This cannula is secured to the patient’s skin with a towel clip placed in the left subcostal area. A 20-French angled-tip cannula is placed in the distal aorta and connected to the inflow line of the LHB circuit (Figure 3). This cannula is secured to the patient’s skin with a towel clip placed near the umbilicus. The inflow line of the LHB circuit has a Y-connector attached that splits pump return between the line going to the distal aortic cannula and another line leading to two 9-French Pruitt balloon-tipped perfusion catheters for later delivery of selective visceral perfusion to the celiac artery and SMA (Figure 3). This selective visceral perfusion line remains clamped while distal aortic perfusion is being provided. A separate cold crystalloid renal perfusion circuit is set up with another two 9-French Pruitt balloon-tipped perfusion catheters attached to the end of its line for later administration of 4 ℃ lactated Ringer’s solution with mannitol (12.5 gm/L)