• A thoracic aortic aneurysm (TAA) is a permanent, localized dilation that is at least 1.5 times the diameter of the expected normal value. Classifications are based on the anatomic location and extent of involvement (Crawford, Debakey, and Stanford).
• Surgical repair often implements partial left heart bypass (LHBP) or femoral-femoral (fem-fem) cardiopulmonary bypass (with selective cerebral perfusion and deep hypothermic circulatory arrest [DHCA]) when the aneurysm is located at the ascending aorta or arch; there is proximal involvement of structures (aortic valve, annulus, sinuses of Valsalva, etc.); it is large in size; or repair is anticipated to be complex or require a long cross-clamp time. These techniques decrease hemodynamic stability and spinal cord ischemia/paralysis. In select cases (e.g., descending aneurysms), repair may be considered without LHBP or fem-fem bypass.
• Following surgical exposure, partial or full heparinization is administered, bypass techniques are implemented, and the aorta is cross-clamped both distal and proximal to the aneurysm. The aneurysm is opened and repaired typically with a Dacron graft. This is followed by declamping, reperfusion, adequate hemostasis, and closure.
• Open surgical repair involves surgical exposure, followed by partial or full heparinization and partial left heart bypass (LHBP) or femoral-femoral (fem-fem) cardiopulmonary bypass (CPB). The aorta is cross-clamped both proximal and distal to the aneurysmal segment, the aneurysm opened and repaired with Dacron graft. This is followed by declamping, reperfusion, adequate hemostasis, and closure.
• Endovascular repair has become a popular approach; it provides the benefit of a less invasive surgical technique with faster recovery and better short-term outcomes.

Right (R) lateral decubitus with hips rotated toward a more supine position.

• Left (L) lateral thoracic
• Median sternotomy for CPB with deep hypothermic circulatory arrest (DHCA) technique

4–5 hours average, depending on surgical experience

500–1,500 mL blood loss, dependent on surgical experience

5–10 days

• Partial LHBP with selective organ perfusion.
• Fem-fem CPB with DHCA and selective cerebral perfusion.

Incidence

• No current feasible screening technique
• 10.4/100,000 person/years; equal in both sexes
• Ascending aorta 51%, aortic arch 11%, descending aorta 38%
• Average growth of 0.07 cm/year in ascending aorta and 0.19 cm/year in descending aorta. Growth rate >1 cm/year is an indication for elective surgical repair.

Prevalence

400/100,000 autopsies by the age of 65.

• Cumulative risk of rupture is 20% at 5 years.
• Risk factors for rupture: Female, elevated diastolic pressure, aneurysm >5 cm, obstructive pulmonary disease.

• 27.4% overall in-hospital mortality for acute aortic dissection
• Type A: 26% surgical management and 58% medical management. Type B: 31.4% surgical management and 10.7% medical management

History

Most frequently diagnosed incidentally

Signs/Physical Exam

Hypertension (HTN) or hypotension, syncope, altered mental status, superior vena cava syndrome, cardiac tamponade (pulsus paradoxus, jugular venous distension, Kussmaul's sign), limb ischemia

Labs/Studies

• Hg, WBC, platelet count/function, PT/PTT, INR, BUN/creatinine
• CT/MRI angiography: 100% sensitivity, as well as assessment of the extension of aneurysms and airway involvement (distortion of L main stem bronchus).
• Angiogram: Accurate diagnosis of the tear points, involvement of the artery of Adamkiewicz, dissection into other major arteries (great vessels, renal, mesenteric, common iliac arteries).
• Carotid Doppler: Evaluate the extent of dissection into carotid arteries, rule out atherosclerotic plaques with potential risk for stroke during selective antegrade cerebral perfusion.
• Pulmonary function tests for preexisting pulmonary disease, COPD, restrictive lung disease, previous lung resection to assess the feasibility of one lung ventilation.
• Echocardiogram and dobutamine stress test for preexisting ischemic cardiomyopathy, coronary stents, pulmonary hypertension (PHTN), right ventricular dysfunction.

• Antihypertensive and antianginal medication should be continued, as appropriate.
• Anxiolytics can minimize HTN and rupture.

• Emergency intervention for unstable cases/altered mental status
• Consent for blood transfusion
• Potential for postoperative intubation
• Potential for spinal cord injury and paralysis

Wide coverage of both gram (+) and (–) germs; Staphylococcus aureus, most common, followed by Salmonella.

• General anesthesia with endotracheal tube (ETT)
• Epidural anesthesia may also be used; however, it poses a higher risk for spinal cord hematoma and makes postoperative neurotesting more challenging.

• Standard monitors and Foley catheter.
• Preinduction radial arterial line (R side for descending aortic procedures, L side for ascending aorta and arch); femoral line after induction (R side for L thoracotomy with LHBP, L side for fem-fem CPB with DHCA technique).
• Large-bore peripheral IVs and multiport central line. A rapid infusion system should be primed and connected. Consider a pulmonary artery catheter for preexisting LV dysfunction, pulmonary HTN.
• Nasopharyngeal temperature (NPT) for brain temperature and bladder temperature (BT) for visceral temperature.
• Spinal drain for monitoring CSF pressure and spinal cord protection.
• Regional cerebral oximetry: Assessment of adequate, bilateral brain oxygenation during CPB with DHCA and selective cerebral perfusion.
• BIS may be considered, particularly for LHBP or fem-fem bypass.
• TEE: Confirmation of the extent and severity of aortic pathology, assessment of volume status, myocardial function, aortic valve function, adequate LV decompression during CPB with DHCA.
• Neuromonitoring: MEP, SSEP, EEG for CPB with DHCA.

• Maintain HD stability and volume status
• Double lumen tubes (DLT) are used to improve visualization for descending aneurysms; usually left-sided (consider a right DLT if the left mainstem bronchus is compressed or distorted).
• Single lumen ETT for ascending aortic and arch surgery.

• LHBP technique is used for partial redistribution of blood from the upper to the lower body, reduction in afterload and myocardial O₂ consumption, and improved SCPP. Heparinize to an activated clotting time of 300 s and maintain flows at 1,000–2,000 mL/min.
• Fem-fem CPB with DHCA. Full heparinization, cool to 18°C, initiate DHCA after 20 min of 18°C core temperature, rewarm slowly with NPT-BT gradient 2°C
• Spinal cord protection
  • Steroids can decrease spinal cord edema; mannitol can enhance free radical scavenging.
  • Lumbar drains may be placed for spinal cord protection when bypass techniques are not used. Spinal cord perfusion pressure is equal to the mean arterial pressure minus the intracranial pressure. CSF is drained in 10 mL aliquots when the lumbar CSF pressure exceeds 10 mm Hg; avoid draining >20 mL/hour.
  • Neuromonitoring.
    • Avoid high levels of volatile agents and consider TIVA (propofol, fentanyl, remifentanil). Boluses should be avoided, particularly at critical times to avoid false positives.
    • Avoid muscle relaxation, if possible; alternatively maintain 2–3 twitches when MEP monitoring is used (this should be discussed with the surgical and neuromonitoring team).
• Avoid muscle relaxation, if possible; alternatively, maintain 2–3 twitches when MEP monitoring is used.
• Spinal cord protection: SCPP = MAP – ICP. CSF is drained for lumbar CSF pressure >10 mm Hg in 10 mL aliquots; avoid draining >20 mL/hour. Steroids and mannitol decrease spinal cord edema and free radical scavenging.
• Aortic clamping is associated with an acute increase in afterload, preload (secondary to volume redistribution), myocardial oxygen consumption, and ICP
• Aortic unclamping is associated with hypotension from hypovolemia, accumulation of vasoactive substances, acidosis, hypocalcemia.
• Coagulopathy is commonly encountered as the result of dilution, hypothermia, quantitative and qualitative platelet dysfunction, heparin effect, and fibrinolysis. Antifibrinolytic use is recommended.

If a DLT was utilized, should be carefully changed to a single lumen ETT (patient may have significant facial and laryngeal edema).