Chapter 31 – Abdominal Aorta and Splachnic Vessels




Abstract






  • For vascular trauma purposes the abdomen is divided into four retroperitoneal anatomical areas:

    • Zone 1: The midline retroperitoneum from the aortic hiatus to the sacral promontory is broken into supramesocolic and inframesocolic areas. The supramesocolic area contains the suprarenal aorta and its major branches (celiac artery, superior mesenteric artery, and renal arteries), the supramesocolic segment of the inferior vena cava with its major branches, and the superior mesenteric vein. The inframesocolic area contains the infrarenal aorta and infrarenal inferior vena cava.
    • Zone 2 (left and right): This is the paired right and left region lateral of Zone 1 containing the kidneys and renal vessels.
    • Zone 3: The pelvic retroperitoneum, which contains the iliac vessels.

  • The abdominal aorta originates between the two crura of the diaphragm at the level of T12–L1 and bifurcates into the common iliac arteries at the level of L4–5. The umbilicus is an approximate external landmark for the aortic bifurcation. The first large branch is the celiac trunk, followed by the superior mesenteric artery 1–2 cm inferiorly, and both course anteriorly and inferiorly. The renal arteries originate 1–2 cm below the origin of the superior mesenteric artery at the level of L2 and course laterally. Finally, the inferior mesenteric artery originates 2–5 cm above the aortic bifurcation on the left anterior aspect of the aorta.

    • Celiac artery: The main trunk originates on the anterior surface of the aorta at the level of T12–L1. It is 1–2 cm long and divides into three branches at the upper border of the pancreas—the common hepatic, left gastric, and splenic arteries. The celiac is encased in extensive fibrous, ganglionic, and lymphatic tissues, which makes surgical dissection of the celiac artery difficult. In 10–20% of patients, the left gastric artery gives off a replaced left hepatic artery that courses through the gastrohepatic omentum and can be injured while mobilizing the left lobe of the liver or lesser curve of the stomach.
    • Superior mesenteric artery (SMA): The SMA originates from the anterior surface of the aorta at the level of L1, 1–2 cm below the celiac artery. It courses posterior to the neck of the pancreas and anterior to the third part of the duodenum, beyond which it enters the root of the mesentery. SMA branches include the inferior pancreaticoduodenal artery, the middle colic artery, an arterial arcade with 12–18 intestinal branches, the right colic artery, and the ileocolic artery. In 10–20% of patients, the SMA gives off a replaced right hepatic artery, which courses posterior to the head of the pancreas and runs posteriorly and to the right of the portal vein.
    • Renal arteries: The right renal artery emerges at a slightly higher level and is longer than the left and courses posteriorly to the inferior vena cava. Approximately 30% of patients have more than one renal artery, usually an accessory artery supplying the lower pole of the kidney. Both renal veins lie anteriorly of their accompanying renal arteries. The left renal vein is significantly longer than the right and courses anteriorly to the aorta. The left renal vein drains the left gonadal vein inferiorly, the left adrenal vein superiorly, and the renolumbar vein posteriorly. The right gonadal vein drains directly into the IVC.
    • Inferior mesenteric artery (IMA): The IMA provides blood supply to the left colon, sigmoid, and the rectum. It communicates with the SMA through the marginal artery of Drummond and arc of Riolan.





Chapter 31 Abdominal Aorta and Splachnic Vessels


Pedro G. Teixeira , Gregory A. Magee , and Vincent L. Rowe



Surgical Anatomy




  • For vascular trauma purposes the abdomen is divided into four retroperitoneal anatomical areas:




    • Zone 1: The midline retroperitoneum from the aortic hiatus to the sacral promontory is broken into supramesocolic and inframesocolic areas. The supramesocolic area contains the suprarenal aorta and its major branches (celiac artery, superior mesenteric artery, and renal arteries), the supramesocolic segment of the inferior vena cava with its major branches, and the superior mesenteric vein. The inframesocolic area contains the infrarenal aorta and infrarenal inferior vena cava.



    • Zone 2 (left and right): This is the paired right and left region lateral of Zone 1 containing the kidneys and renal vessels.



    • Zone 3: The pelvic retroperitoneum, which contains the iliac vessels.




  • The abdominal aorta originates between the two crura of the diaphragm at the level of T12–L1 and bifurcates into the common iliac arteries at the level of L4–5. The umbilicus is an approximate external landmark for the aortic bifurcation. The first large branch is the celiac trunk, followed by the superior mesenteric artery 1–2 cm inferiorly, and both course anteriorly and inferiorly. The renal arteries originate 1–2 cm below the origin of the superior mesenteric artery at the level of L2 and course laterally. Finally, the inferior mesenteric artery originates 2–5 cm above the aortic bifurcation on the left anterior aspect of the aorta.





    Figure 31.1 Retroperitoneal vascular zones. Zone 1 includes the midline vessels from the aortic hiatus to the sacral promontory; Zone 2 the paracolic gutter and the kidneys; Zone 3 the pelvic retroperitoneum.





    Figure 31.2 Lateral view of the major abdominal branches of the aorta. Note the tight concentration of the supramesocolic vessels: celiac artery, superior mesenteric artery (SMA), and renal arteries.





    Figure 31.3 Anatomy of the major branches of the abdominal aorta. Note the site of division (dashed line) of the left crus of the diaphragm at 2 o’clock to avoid the inferior phrenic artery for exposure of the lower thoracic aorta.




    • Celiac artery: The main trunk originates on the anterior surface of the aorta at the level of T12–L1. It is 1–2 cm long and divides into three branches at the upper border of the pancreas—the common hepatic, left gastric, and splenic arteries. The celiac is encased in extensive fibrous, ganglionic, and lymphatic tissues, which makes surgical dissection of the celiac artery difficult. In 10–20% of patients, the left gastric artery gives off a replaced left hepatic artery that courses through the gastrohepatic omentum and can be injured while mobilizing the left lobe of the liver or lesser curve of the stomach.



    • Superior mesenteric artery (SMA): The SMA originates from the anterior surface of the aorta at the level of L1, 1–2 cm below the celiac artery. It courses posterior to the neck of the pancreas and anterior to the third part of the duodenum, beyond which it enters the root of the mesentery. SMA branches include the inferior pancreaticoduodenal artery, the middle colic artery, an arterial arcade with 12–18 intestinal branches, the right colic artery, and the ileocolic artery. In 10–20% of patients, the SMA gives off a replaced right hepatic artery, which courses posterior to the head of the pancreas and runs posteriorly and to the right of the portal vein.



    • Renal arteries: The right renal artery emerges at a slightly higher level and is longer than the left and courses posteriorly to the inferior vena cava. Approximately 30% of patients have more than one renal artery, usually an accessory artery supplying the lower pole of the kidney. Both renal veins lie anteriorly of their accompanying renal arteries. The left renal vein is significantly longer than the right and courses anteriorly to the aorta. The left renal vein drains the left gonadal vein inferiorly, the left adrenal vein superiorly, and the renolumbar vein posteriorly. The right gonadal vein drains directly into the IVC.



    • Inferior mesenteric artery (IMA): The IMA provides blood supply to the left colon, sigmoid, and the rectum. It communicates with the SMA through the marginal artery of Drummond and arc of Riolan.




General Principles




  • Abdominal and pelvic vascular injuries result in noncompressible hemorrhage. Immediate operative intervention is the cornerstone of survival.



  • Penetrating abdominal vascular injuries are usually associated with hollow viscus injuries, which increase the complexity of the operation and expose the vascular repair to enteric contamination.



  • In patients with multiple potentially fatal injuries, who are too unstable to undergo definitive repair of a critical vessel, a temporary shunt can be placed with a plan for delayed definitive reconstruction.



  • Abdominal arterial and venous injuries occur with the same incidence. The most commonly injured abdominal vessel is the IVC, followed by the aorta, due to their relative size.



  • In suspected abdominal vascular injuries, where the IVC or iliac veins may be injured, the common femoral veins should not be used for venous access.



  • Patients with severe intra-abdominal hemorrhage compensate their central blood pressure by maximal peripheral vasoconstriction and as such, they are at high risk of rapid decompensation and cardiac arrest during induction of anesthesia that causes peripheral vasodilation. Therefore, the patient should be prepared and draped, with the surgical team ready to commence the operation prior to the induction of anesthesia, whenever possible.



  • The feasibility of systemic anticoagulation with heparin is limited by trauma-induced coagulopathy; however, heparinized saline (5,000 units in 100 mL saline) should be liberally injected into injured vessels with little risk of worsening bleeding.



  • Approximately 15% of patients with intra-abdominal vascular injuries arrive in cardiac arrest. These patients may benefit from a left anterolateral resuscitative thoracotomy and cross-clamping of the thoracic aorta. Resuscitative endovascular balloon occlusion of the aorta (REBOA) should be used with caution in patients with concern for aorta or iliac artery injuries, as blind placement of the REBOA catheter can worsen these injuries.



Special Surgical Instruments




  • In addition to a standard trauma laparotomy instrument tray, vascular clamps and needle drivers with multiple lengths and angulations must be available.



  • A self-retaining retractor, such as Omni-Tract or Bookwalter is extremely helpful in providing adequate exposure.



  • A U-shaped aortic compression device should be available for temporary aortic control just below the diaphragm. If this is not available, a sponge stick or manual pressure can be used.



  • Surgical headlamp and magnifying loupes are useful.



  • A thoracotomy instrument tray with a Finochietto retractor should be available, should a left anterolateral thoracotomy be necessary, for aortic cross-clamping.



Positioning




  • Supine, with upper extremities abducted to 90°. Skin antiseptic preparation should include the chest, abdomen, and thighs, in anticipation of a possible thoracotomy or venous conduit harvesting.



Incision




  • Extended midline trauma laparotomy, from xiphoid to pubic symphysis.



  • For proximal aortic control in cases with high supramesocolic bleeding or hematoma, a left anterolateral thoracotomy through the fifth intercostal space may be needed. REBOA is rarely useful in this situation, as supramesocolic aortic reconstruction will require its removal.



Exposure




  • Upon opening the peritoneal cavity, the usual findings include free intraperitoneal bleeding, or a retroperitoneal hematoma, or a combination of the two. The retroperitoneal hematoma may or may not be expanding or pulsatile. Intraperitoneal hemorrhage can be due to solid organ injury, mesenteric injury, or major vascular injury and the surgeon needs to evaluate for each.



  • The management of retroperitoneal hematomas depends on the mechanism of injury.




    • As a general rule, almost all hematomas due to penetrating trauma should be explored, irrespective of size. Often, underneath a small hematoma there is a vascular or hollow viscus perforation. The only exception to this recommendation is a stable and nonexpanding retrohepatic (Zone 4) hematoma. Surgical exploration of the retrohepatic vena cava or the hepatic veins is challenging and may result in uncontrollable bleeding. If, for some reason, a hematoma is not explored, postoperative CT angiographic evaluation should be considered.



    • Retroperitoneal hematomas due to blunt trauma rarely require exploration because of the very low incidence of underlying vascular or hollow viscus injuries requiring surgical repair. The only indications for exploration of hematomas due to blunt trauma include a paraduodenal hematoma, large expanding or leaking hematoma, and a hematoma in the region of the superior mesenteric artery associated with ischemic bowel.




Exploration of Zone 1



Supraceliac Aortic Control


Sep 4, 2020 | Posted by in EMERGENCY MEDICINE | Comments Off on Chapter 31 – Abdominal Aorta and Splachnic Vessels
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