ABDOMINAL AORTIC ANEURYSM (AAA) REPAIR

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Open abdominal aortic aneurysm (AAA) repair is a surgical procedure performed to treat an abdominal aortic aneurysm. An abdominal aortic aneurysm is a bulge or dilation in the aorta, the largest artery in the body, which runs through the abdomen. If left untreated, an AAA can rupture, leading to life-threatening internal bleeding and potential death

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The open AAA repair procedure involves the following steps:

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1. Anesthesia: The patient is administered general anesthesia, rendering them unconscious and unable to feel pain during the surgery.

2. Incision: The surgeon makes a long incision in the abdomen, usually along the midline, to access the aorta.

3. Exposure of the aorta: The surgeon carefully exposes the aorta and the aneurysm, temporarily clamping the blood flow above and below the aneurysm to prevent excessive bleeding.

4. Removal of the damaged aortic segment: The surgeon opens the aneurysm sac and removes any blood clots or debris. They then carefully remove the damaged section of the aortic wall.

5. Graft placement: A synthetic tube-like graft, made from materials like Dacron or polytetrafluoroethylene (PTFE), is sewn in place to replace the removed section of the aorta. The graft is designed to be durable and resistant to infection.

6. Reestablishing blood flow: The surgeon releases the clamps above and below the graft, restoring blood flow through the aorta and checking for any leaks around the graft.

7. Closure: Once the graft is securely in place and blood flow is normal, the surgeon closes the aneurysm sac around the graft, if possible, and sutures the abdominal incision.

 

Open AAA repair has been the gold standard for treating abdominal aortic aneurysms for many years. However, in recent years, endovascular aneurysm repair (EVAR) has become a popular alternative, as it is less invasive and has a shorter recovery time. The choice between open AAA repair and EVAR depends on factors such as the patient's overall health, anatomy, and the size and location of the aneurysm. The surgeon will evaluate these factors and determine the most appropriate treatment approach for each patient.

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                                                                           Anesthetic Implications for AAA

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Anesthesia type: General

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Airway: Endotracheal tube

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Preoperative:

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• Identify high-risk patients for preoperative optimization

• Risk factors of abdominal aortic aneurysm (AAA): increasing age, male gender, smoking, elevated plasma cholesterol levels, hypertension, and family history 

• Patients may have COPD and history of smoking

• Patients are vasculopathic

• Coronary artery disease (CAD) is present in 30–40% of patients with AAA.

• Assume patients have disease of cerebral, cardiac, renal, and peripheral vasculature

• Smoking is the greatest risk factor

• Surgical repair of a AAA is recommended once the aneurysm expands to more than 5 cm

• Large bore venous access and arterial line should be placed

• Consider central venous access for longer procedures

• 5-lead electrocardiogram (monitor for ST changes) 

• Evoked potentials monitoring may be requested for high-risk of spinal cord ischemia (SCI) patients

• Have access to rapid infusion devices

• Have IV fluid warmers and blood transfusion tubing available

• Patients are commonly on antiplatelet medications

• Bladder catheterization is indicated to monitor urine output

• The abdominal aorta begins in the diaphragm at T12 and ends at L4

• The hallmark presentation for ruptured AAA Is severe back or abdominal pain

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Intraoperative:

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• Ensure a smooth induction and cardiovascular stability

• Hypertension and tachycardia should be avoided on induction

• Type and screen and blood available in room

• Maintain blood pressure within 20% of the baseline

• Bradycardia is better than tachycardia

• 5 lead EKG with ST segment analysis

• Large bore IV and arterial line are placed

• May use of cell-saver technology.

• Have rapid infuser capability available

• When hemostasis is achieved the cross-clamps are released.

• Spinal cord perfusion in the thoracolumbar area is derived from the artery of Adamkiewicz

• Position: supine (midline abdominal incision) or lateral decubitus (retroperitoneal exposure)

• Prior to the cross-clamp is applied, heparin 100 units/kg IV is administered at the surgeon's request 

• Heparinization and activated clotting time (ACT) checks 3 min after heparin and every 30 min thereafter

• Expect wide fluctuations in systemic vascular resistance with aortic cross-clamping and unclamping

• Decrease MAP before cross-clamp application (SBP around 90 mm Hg)

• Once the proximal aorta is clamped, there is an increase in blood pressure, SVR (afterload) and impedance to aortic flow above the clamp. Decreased venous return (preload)

• Myocardial oxygen demand increases and myocardial dysfunction can occur

• Monitor for left ventricle failure and myocardial ischemia

• When cross-clamping is on, SBP is normally maintained at 140–160 mm Hg for organ perfusion

• Document the cross-clamp application time (start of ischemic time)

• Prior to the cross-clamp being removed, provide volume loading and have vasopressors available

• Clamp removal is associated with hypotension, metabolic washout, and acidosis (ETCO2 increases)

• Metabolites cause vasodilation and myocardial depression

• Mannitol may be administered to maintain urine output and decrease the production of thromboxane

• Document the cross-clamp removal time (end of ischemic time)

• The surgeon can reclamp the aorta if hypotension persists 

• Minimizing renal impairment: adequate hydration, limiting contrast, avoidance of nephrotoxic drugs

• Muscle relaxation is indicated

• Traction on the intestines and aortic cross-clamping can be associated with mesenteric mast cell release histamine (decreased systemic vascular resistance (SVR), hypotension, tachycardia)

• Hypothermia can cause dysrhythmias, depress cardiac contractility, and worsen coagulopathy

• Duration 3-5 hours

• EBL 500 ml

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Postoperative:

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• Smooth emergence

• Maintain hemodynamic stability

• Prevent hypertension and tachycardia on emergence

• Avoid coughing and bucking on emergence

• Assure full reversal of neuromuscular blockers

• Assess distal extremity circulation

• Epidural catheter for postop analgesia may be placed

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Complications:

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• Death related to elective AAA repair commonly occurs from myocardial infarction

• Paraplegia

• Hemmorhage

• Mesenteric and bowel ischemia

• Myocardial infarction

• Renal ischemia and failure (from suprarenal or infrarenal aortic cross-clamping)

• Hepatic ischemia with coagulopathy

• Stroke

• Coagulopathy

• Hypothermia

• Respiratory failure

• Postoperative atelectasis

• Pneumonia 

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Sources:

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Elisha, S. (2010). Case Studies in Nurse Anesthesia.

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Macksey, L. F. (2011). Surgical procedures and anesthetic implications: A handbook for nurse anesthesia practice. 

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Jaffe, R. A. (2020). Anesthesiologist's Manual of Surgical Procedures (6th ed.). 

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Singh-Radcliff, N. (2013). 5-Minute Anesthesia Consult.

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