AA Aneurysm Open

Open Abdominal Aortic Aneurysm (AAA) Repair

Overview

• The open AAA repair procedure is becoming rarer due to the rise of endovascular stent placements.
• It is associated with significant blood loss and complexity.

Procedure Description

• Repair is performed through a midline abdominal incision.
• Most open AAA procedures have been replaced by endovascular AAA repair.
• Elective surgery is recommended for aneurysms greater than 5 cm in diameter.
• Repair methods include:

 * Straight tube graft
 * Aorta to bilateral iliac graft replacement

Symptoms

• Typically asymptomatic, but may present with lumbar back or abdominal pain.

Imaging

• Methods include CT scan, MRI, basic x-ray, or angiography.
• CT angiography is preferred as it provides details on size, location (infra- or supra-renal), and the status of major branches (e.g., inferior mesenteric artery).

Causes

• Atherosclerosis
• Marfan syndrome
• Ehlers-Danlos syndrome
• Dissection
• Congenital vasculitis
• Infections, including syphilis

Preoperative Tips

• Maintain patient warmth.
• Keep heart rate slow (avoid tachycardia).
• Prevent anemia (keep hematocrit (HCT) >25-30).
• Prevent hypertension to avoid stressing the aneurysm.

Procedure Details

• The surgeon cross-clamps above and below the aneurysm, opens the aorta, removes the diseased section, and replaces it with a graft.
• Clamps are then removed; estimated blood loss (EBL) can be substantial.
• Be aware of hemodynamic changes during clamping and unclamping.

Preoperative Preparation

• Verify if the patient has had a thorough cardiac workup; if not, treat them as a coronary artery disease (CAD) patient.
• Line and Monitoring:

 * Use the largest bore peripheral IVs available (14G if possible).
 * Right internal jugular (IJ) line is recommended.
 * Consider a transesophageal echocardiogram (TEE) instead of a Swan-Ganz catheter for monitoring left ventricular filling status.
 * Have fluid warmers (1-2) and rapid transfusers or pressure bags ready.
 * Prepare blood transfusion tubing (2) with normal saline (NSS).
 * Use a cell saver and warming blankets (2).

Induction and Intubation

• To avoid hypertension with direct laryngoscopy:

 * Consider adding Esmolol to induction to mitigate BP spikes.
 * Use Remifentanil (0.5-1 mcg/kg/min) 8 minutes before intubation.
 * High narcotic induction doses may be used.
 * Consider a GlideScope to reduce stimulation.

• Anesthesia:

 * General anesthesia with endotracheal tube (ETT).
 * Thoracic epidural is recommended; administer before the incision.
 * Rapid Sequence Induction (RSI) is often utilized.
 * Nasogastric (NG) tube is advisable.

• Duration: 3-5 hours.
• Position: Supine with arms tucked.
• Estimated Blood Loss (EBL): 500-1,000 mL.

Common Intubation Doses

• Fentanyl: 10-20 mcg
• Midazolam (Versed): 5 mg
• Large narcotic doses may cause rigidity; these reduce the need for volatile agents during induction.

Pre-Induction

• Use a priming dose of a non-depolarizing muscle relaxant or succinylcholine for RSI.
• Connect fluids to the warmer as soon as possible.
• Keep the patient covered; use a Bair Hugger after central line placement.
• Administer a 200-500 cc fluid bolus before induction.

Induction to Pre-Clamp Period Goals

• Avoid hypertension to prevent aneurysm rupture.
• Administer 0.5 g/kg Mannitol (typically 12.5-25 g) 30 minutes before cross-clamping.
• Have Lasix available and follow the surgeon’s instructions for administration.

Preparation for Aortic Cross-Clamping

• Ensure nitroglycerin and/or Milrinone are available.
• Monitor ionized calcium (Ca) levels.
• Maintain volume and prepare to manage BP drops when unclamping.

Complications of Aortic Cross-Clamping

• Renal failure:

 * Increased risk with preexisting renal disease, cross-clamp time >30 minutes, and hypovolemia/decreased cardiac output without bypass.
 * Renal protection may include Mannitol (0.5-1.0 g/kg) before clamping, and potentially Lasix, Dopamine, and Fenoldopam.

• Paraplegia:

 * The anterior spinal cord is most prone to ischemia due to its single arterial supply.
 * Prolonged ischemia can occur with cross-clamping times >30-45 minutes or during perioperative hypotension.

Methods to Prevent BP Drops with Unclamping

• Decrease anesthetic depth.
• Maintain a hypervolemic state while clamped.
• Infuse Neosynephrine before clamp removal.
• Unclamp slowly as per the surgeon’s direction.

Unclamping Effects

• Reactive hyperemia due to reduced systemic vascular resistance (SVR) from metabolites in ischemic tissue.
• Lactic acid causes vasodilation.
• Consider NaHCO3 if requested by the surgeon.
• Increase minute ventilation to manage acidosis; hypocarbia will constrict vessels and redirect blood flow to ischemic tissues.

Late Operative and Postoperative Considerations

• Common issues:

 * Facial, scalp, and airway edema.

• Recommendations:

 * Delay extubation until edema subsides.
 * Elevate the head of bed (HOB) overnight.
 * Monitor for fluid shifts postoperatively to address potential pulmonary issues.

Spinal Cord Blood Supply

• Supplied by:

 * One anterior spinal artery.
 * Two posterior spinal arteries.
 * A network of small segmental spinal arteries.

• The anterior spinal cord is particularly vulnerable to ischemia due to its single arterial supply.

Possible Complications

• Ruptured aneurysm
• Cardiac and pulmonary problems
• Nerve damage causing pain or numbness in the legs
• Damage to intestines or nearby organs
• Graft infection
• Injury to the ureter(s)
• Incisional hernia
• Spinal cord injury
• Sexual dysfunction
• Lower extremity paralysis
• Death