Anesthesia for Aortic Surgery

Coexisting Diseases

• CAD, HTN, DM and smoking are common coexisting diseases
• CVD is common, and most vascular patients will have CAD
• Renal disease is common
• Postoperative mortality is highest after a MI

Abdominal Aortic Aneurysm (AAA)

• AAA occurs when the abdominal aorta is below the diaphragm
• 90-95% of AAAs are infrarenal
• AAAs are common in the elderly
• AAAs have a potential genetic link
• AAAs are common in patients with atherosclerosis
• Symptoms can include abdominal, back, or groin pain, syncope, abdominal mass, or paralysis.

Types of Aneurysms

• Aortic dissection is a tear in the intimal layer and allows blood to enter between the layers
• Dissection can narrow or compress the vessel lumen, which obstructs blood flow
• Ruptured dissection symptoms include hypotension, while secondary to pain, HTN can occur
• Type A dissection typically involves the ascending aorta, and symptoms of both type A and type B may be present
• Type A dissection symptoms include ripping or tearing chest pain and a new onset of diastolic murmur
• Type A dissection is dangerous due to the high risk of cardiac tamponade, aortic regurgitation, myocardial infarction, and stroke
• Type A dissection requires surgical emergency with immediate open repair
• Type B dissection typically involves the descending aorta
• Type B dissection is typically medically managed first unless there is rupture or malperfusion
• Type B dissection symptoms include tearing back or abdominal pain with possible signs of lower limb or visceral ischemia
• False Aneurysm involves one or more layers of the vessel wall and dilation is formed by surrounding tissues
• False Aneurysm is not the same as a dissection
• False Aneurysm is a contained rupture of a blood vessel where blood escapes through the intima and media but is held by adventitia/surrounding tissue
• Aortic aneurysm is a localized dilation or bulging of a vessel wall
• All 3 layers of the blood vessel are involved in aortic aneurysms
• True Aneurysm involves all three layers of the vessel wall
• Tunica externa is a tough fibrous external layer, tunica media is the smooth muscle middle layer, and tunica interna is the epithelial inner wall
• Repair is required when the aneurysm size is >5 cm
• Immediate rupture risk occurs when the aneurysm is >7 cm
• The Crawford classification system classifies aortic aneurysms based on their involvement in the thoracic and abdominal aorta

Treatment

• AAA treatment options include bypass graft inside the artery, oversewing the aorta, or using a Gore-Tex graft
• Most procedures are now endovascular with a bypass graft
• Graft placement may occlude aortic branches
• Open procedures involve major blood loss and increased morbidity & mortality (M&M)
• Emergent cases (leaks/ruptures) have a higher mortality rate

Endovascular Surgery

• Endovascular surgery was FDA approved in 2000
• Endovascular surgery can be done under MAC or GA
• Access is done via both groins & right arm
• Endovascular surgery reduces mortality & morbidity via minimally invasive techniques
• Endovascular aneurysm repair (EVAR) does not require cross-clamping

Disadvantages of AAA Repair

• There is a risk of leaks if the graft does not fully exclude the AAA
• Follow-up serial CT scans are required
• The graft may be placed over branches

Complications and Risks

• Rupture risk is high if >5 cm
• Organs can be affected by decreased blood flow to the abdominal organs
• Decreased blood flow to the spine causes spine ischemia
• Cardiac & Pulmonary issues are concerns

Cardiac Considerations

• High risk of MI is the leading cause of postoperative mortality
• Perioperative MI survival rate is only 1/3

Renal, Colon, & Hepatic Blood Flow Considerations

• Implications of infrarenal & suprarenal clamps require focusing on maintain cardiac output, minimizing nephrotoxic medications, and maintaining urine output (1 mL/kg/hr)
• Pre-treat with Mannitol for 20-30 min pre-clamp and Dopamine (0.25 mg/kg) or Lasix to reduce renal workload
• Colon and hepatic blood flow decreases/stops
• The liver's blood supply includes the portal vein (75%) and the hepatic artery (25%)
• Artery of Adamkiewicz is commonly implicated in spinal ischemia.
• It is one of the main radicular arteries that provides collateral flow in the thoracolumbar region of the spine
• Interruption of flow can cause spinal cord ischemia, leading to anterior spinal artery syndrome (aka Beck’s syndrome)
• An aortic cross-clamp placed above the artery of Adamkiewicz causes ischemia to the lower portion of the anterior spinal cord
• Beck syndrome signs and symptoms are flaccid paralysis of lower extremities, bowel and bladder dysfunction, loss of pain and temperature, preserved touch and proprioception

Monitoring

• Monitoring options include SSEPs, MEPs, and lumbar drain

Aortic bi-fem bypass

• Aortic bi-fem bypass is performed if there is blockage of the abdominal aorta obstructing flow to femoral arteries
• It is performed by removing the diseased portion of the abdominal aorta and replacing with a synthetic graft or the patient's own vessels from the aorta to the femoral artery.

Thoracic Aneurysm

• Causes include trauma, aneurysm, coarctation, occlusive disease, or dissection
• Typically requires CPB (Cardiopulmonary Bypass)
• Complications include large blood loss, intraoperative MI, renal/spinal ischemia, and Preoperative HTN
• May require circulatory arrest

Considerations

• Tracheal & bronchial compression are possible
• Laryngeal nerve compression is possible
• Symptoms include pain in chest or back
• Ascending locations include the aortic valve to innominate artery
• Arch locations include the innominate artery to left subclavian artery
• Descending locations include the left subclavian artery distally
• Risk of cord ischemia

Marfan’s Syndrome & Aneurysms

• Marfan's Syndrome is a genetic disorder characterized by unusually tall stature, long limbs, thin fingers & toes
• It involves multiple organs.
• Affects heart valves and causes aortic dissection

Ascending Aneurysm Repair

• CPB is commonly used
• There is a risk of long cross-clamp times → large blood loss
• FEM-FEM bypass may be considered with sternotomy due to rupture risk
• Right radial A-line placement should be done

Aortic Arch Repair

• Requires sternotomy
• CPB may be used. ECMO is an alternative if CPB is not possible
• Cerebral protection strategies involve reducing CMRO₂ by cooling the head or using ice packs around the head
• Cerebral protection strategies require tympanic temperature monitoring of the patient
• Ischemic time >40 min significantly increases mortality

Descending Arch Repair

• Descending Arch Repair uses a left thoracotomy approach with right lung ventilation
• Descending Arch Repair involves monitoring with A-line, CVP, Large IVs, possible SSEP

Descending Aortic Repair

• Clamping drastically increases SVR and has the risk of pulmonary edema
• Limit fluids and maintain deep anesthetic depth with NTG or nitroprusside drips
• Consider administering mannitol

Cross-Clamping Effects

• The closer the cross-clamp is to the heart, the more areas are distal to the clamp and at risk for ischemia
• Avoid HTN prior to clamping, so as not to rupture the aneurysm
• The infrarenal area is the most common place for a cross-clamp
• When the aorta is clamped, high pressures are needed to perfuse the organs that are distal to the clamp
• The body relies on collateral circulation to supply the kidneys and spine
• Give fluids to prevent a BP drop when the surgeon unclamps the aorta
• Complications of cross clamping include renal failure due to ischemia and anterior spinal cord syndrome

Severe Increase in SVR → Hypertension

• Can be caused by blood volume shifting proximal to clamp, increased preload and SVR, and increased myocardial workload and O2 demand
• Management includes fluid loading, turning off vasodilators, increasing minute ventilation to blow off CO2 from acidosis below the clamp, and having pressors ready
• Prolonged clamp times increase the Risk of paralysis & renal damage

Clamp Release Effects

• Unclamping can reactive hyperemia because of a drop in SVR from metabolites in ischemic tissue, increased anaerobic metabolism of tissues below the clamp causing increased lactic acid/prostaglandins/metabolic acidosis, and washout of anaerobic metabolites resulting in vasodilation

Severe decrease in SVR → Hypotension

• Management includes fluid loading, turning vasodilators off, pressors, and ventilation
• Potential complications include paralysis and renal impairment

TEE

• Indications include preop and intraop
• TEE can be contrasted TTE
• TEE has complications
• Contraindications can either be absolute or relative
• TEE enables measurements of the heart
• Useful to observe Signs of Myocardial ischemia as well as signs of PE/air embolus/amniotic fluid embolus