Chapter 46. Thoracic Aortic Occlusion

Temporary thoracic aortic occlusion should be performed during an Emergency Department thoracotomy for hypovolemic shock. It preserves cerebral and coronary artery perfusion pressure.1 The blood flow to the viscera below the cross clamp, however, falls to less than 10% of baseline flow.2 This can be advantageous since it stops distal hemorrhage, but it can later result in the undesired metabolic consequences of acidosis, hyperkalemia, and multiple organ system failure.3,4

The aorta begins at the left ventricle and gives rise to the arteries of the body, directly or indirectly (Figure 46-1). It leaves the ventricle and is directed upward as the ascending aorta. It arches to the left and backward at the level of the sternal angle to become the aortic arch. The arch gives rise to the brachiocephalic trunk, left common carotid artery, and left subclavian artery. The aortic arch is directed inferiorly after giving rise to the left subclavian artery and is known as the descending aorta. The descending aorta is subdivided into the thoracic portion above the diaphragm and the abdominal portion below the diaphragm. It descends through the posterior mediastinum, lying first against the left side of the fifth thoracic vertebral body. As it descends, it gradually approaches the midline of the 12th thoracic vertebral body, at which point it passes through the diaphragm.

The esophagus is a thin, muscular tube measuring approximately 2.0 to 2.5 cm in diameter. It descends along the vertebral bodies. It travels forward, away from the vertebral bodies, and to the right at the level of the ninth thoracic vertebral body. It traverses the diaphragm at the level of the 10th thoracic vertebral body. It lies posterior and medial to the descending thoracic aorta throughout most of its course. It migrates as it travels distally, so that its lower part lies in front of the aorta just above the diaphragm (Figure 46-1).

The primary reason to occlude the descending thoracic aorta is to temporarily direct blood flow from below the diaphragm to preserve flow to the brain and heart. The descending thoracic aorta may be occluded in patients with penetrating thoracic or abdominal trauma in which hypovolemic shock and clinical deterioration are not responsive to aggressive fluid resuscitation and blood transfusion. These patients should have the appropriate indications to perform an anterolateral thoracotomy (Chapter 42). The thoracic aorta may also be occluded immediately prior to laparotomy if the patient has a tense abdomen filled with blood. The abdominal incision will decompress the abdomen and result in hypotension, decreased coronary and cerebral perfusion pressure, exsanguination, and death. Uncontrollable hemorrhage below the diaphragm can be controlled by temporarily occluding the descending thoracic aorta.

There are no absolute contraindications to temporarily occluding the descending thoracic aorta after performing an anterolateral thoracotomy. The thoracotomy should not be performed if the patient has obvious signs of death, no vital signs in the field, or no vital signs for over 15 minutes.

• Satinsky, or other, atraumatic vascular clamp (Figure 46-2)
• Metzenbaum scissors
• DeBakey or large Kelly clamp
• Nasogastric tube
• Aortic compressor, Conn or homemade
• Gauze 4 × 4 squares

No preparation is required other than that of performing a thoracotomy and a pericardiotomy (Chapter 42). The patient should be intubated, ventilated with 100% oxygen, and fully monitored (i.e., telemetry, a noninvasive blood pressure cuff, and pulse oximetry). Insert a nasogastric tube. Instruct a nurse to administer intravenous broad-spectrum antibiotics that cover skin flora, gram-positive organisms, and gram-negative organisms. The Emergency Physician should wear full personal protective equipment to protect themselves from contact with the patient's blood and body fluids. While time is of the essence and this is an emergent procedure, aseptic technique should be followed.

Identify the aorta by palpation. It is often easier to identify and isolate the aorta just above the diaphragm. In this location, the aorta is slightly separated from the adjacent esophagus. Elevate the left lung with the nondominant hand superiorly and medially. Instruct an assistant to maintain the lung out of the way. Place the dominant hand through the thoracotomy incision and into the posteroinferior recess of the thoracic cavity. Advance the hand along the diaphragm and toward the midline. The fingers will first encounter the vertebral bodies. The next palpable structure is the aorta. It lies anterior to the vertebral bodies. The aorta may be difficult to palpate if it is collapsed in the patient with hypovolemic shock. In the elderly, the aorta may be significantly calcified, which helps to identify it despite hypovolemia. The aorta is covered by the mediastinal pleura. Place the thumb and index finger of the nondominant hand over the aorta just above the diaphragm.

Isolate the aorta. Bluntly dissect open the mediastinal pleura overlying the aorta with a DeBakey clamp or a large curved Kelly clamp. Never use a scalpel to open the mediastinal pleura, as it may lacerate the aorta. Some physicians may prefer to use a Metzenbaum scissors to dissect and open the mediastinal pleura. Identify the aorta by palpation. Bluntly separate the aorta from the esophagus with the dominant hand. It may be extremely difficult to separate the aorta from the esophagus in the patient with hypotension, hypovolemia, and/or shock. Place a nasogastric tube if this has not been done previously. The nasogastric tube will be palpable within the esophagus and can be used to identify the esophagus. Hook the dominant index finger around the aorta. Use the finger to separate the aorta from the vertebral bodies. The dissection should not be extensive. It should free approximately 3 to 4 cm of the descending thoracic aorta.

Direct Compression

Direct compression of the aorta is fast and simple, it does not interfere with the operative field, and it causes less damage than the application of a clamp. Digital compression is often ineffective. Aortic compression devices have a unique shape to occlude the aorta atraumatically by compressing it against the vertebral bodies. It may be applied before or after the aorta is isolated. Homemade compression devices may use rubber tubing to occlude the aorta5 (Figure 46-3A). The Conn compressor is commercially available and uses a metal plate to occlude the aorta (Figure 46-3B). Place the distal end of the compression device against the distal descending thoracic aorta (Figure 46-3C). Apply downward pressure to occlude the aorta. The degree of occlusion can be controlled by increasing or decreasing the pressure applied to the aorta.

Cross-Clamping

The descending thoracic aorta is most commonly occluded with an atraumatic or Satinsky vascular clamp. Aortic compression devices are rarely available in Emergency Departments or on thoracotomy trays. The aorta must first be separated and isolated from the esophagus, as described above. Place an index finger behind the descending thoracic aorta to elevate it away from the underlying esophagus (Figure 46-4A). Place the Satinsky or other atraumatic vascular clamp over the aorta. One jaw should be posterior to the aorta and adjacent to the index finger while the other jaw is anterior to the aorta. Clamp the aorta and remove the index finger (Figure 46-4B).

It is imperative not to clamp the esophagus. Do not clamp the aorta before it is dissected from the esophagus. Esophageal injury can lead to perforation, ischemia, and sepsis if the patient is resuscitated. Ideally, the clamp should be placed under direct visualization of the aorta. Unfortunately, this is not always practical. The index finger under the aorta can confirm the proper isolation of the aorta and the proper position of the jaws of the clamp before the aorta is occluded.

If—after the thoracotomy, open cardiac massage, and aortic cross-clamping—there is return of a cardiac rhythm and a carotid pulse, the patient must be taken immediately to the Operating Room for definitive treatment. Cover the thoracotomy wound with saline-moistened gauze and a simple dressing. The patient's blood pressure in the upper extremity should be monitored every 30 to 60 seconds after the aorta is occluded. An elevated blood pressure can result in a hemorrhagic stroke or left ventricular failure. Elevated blood pressure will require intermittent release of the aortic occlusion and/or pharmacologic management. Parenteral broad-spectrum antibiotics should be administered to prevent infection if not done previously.

Intercostal arteries arising from the thoracic aorta can be damaged during mobilization of the aorta. This will result in troublesome bleeding that requires operative control. The aorta, vena cava, or the esophagus can be damaged by the clamp. Aortic cross-clamping can precipitate hypertension, stroke, and left-sided heart failure. If the patient is successfully resuscitated, this should be dealt with by periodically releasing the clamp. Lack of blood flow through the artery of Adamkiewicz will cause ischemia of the distal spinal cord. There is a 5% incidence of paraplegia when the blood supply to the distal aorta and spinal cord is disrupted. This incidence increases dramatically when the spinal cord is ischemic for more than 30 minutes.6

Aortic cross-clamping causes visceral ischemia. The gut loses its barrier function and becomes a cytokine-generating organ, which leads to a systemic inflammatory response and multiple organ failure. Renal and liver failure can result from a lack of blood flow.

The organs distal to the aortic clamp become severely ischemic and receive only 10% of the basal cardiac output. The anaerobic metabolism in these organs generates lactic acid. When the aortic clamp is released, acid and potassium are released into the central circulation and can cause a cardiac arrest. Thus, bicarbonate must be given at this time and the cardiac rhythm monitored carefully.

Aortic cross-clamping is a useful adjunct to open cardiac massage in hypovolemic shock. It can help salvage patients by increasing coronary and cerebral perfusion. It may be performed as a lifesaving and temporizing measure until the patient can be taken to the Operating Room for definitive management.