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 use of the Emergency Department thoracotomy is likely to decrease as the resuscitative endovascular balloon occlusion of the aorta (REBOA) technique (Chapter 74) becomes more established and available.
ANATOMY AND PATHOPHYSIOLOGY
The aorta begins at the left ventricle and gives rise to the arteries of the body, directly or indirectly (Figure 58-1). 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.
Anatomy of the aorta and surrounding structures of the mediastinum and left hemithorax. The mediastinal pleura has been removed to visualize the underlying structures.
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 58-1).
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 54). The thoracic aorta may ...