AA Aneurysm Open

Open Abdominal Aortic Aneurysm (AAA) Repair

• **Overview:**

 * Open AAA repair is becoming rarer due to the availability of endovascular stent placements.
 * The procedure is associated with large blood loss and is complex.

• **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 * Most open AAA procedures have been replaced by endovascular AAA repair.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 >5 cm in diameter.
 * Repair methods:
   * Straight tube graft
   * Aorta to bilateral iliac graft replacement

• **Symptoms:**

 * Usually asymptomatic, but may present with lumbar back or abdominal pain.

• **Imaging:**

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

• **Causes:**

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

• **Preoperative Tips:**

 * Keep the patient warm.
 * Maintain a slow heart rate (avoid tachycardia).
 * Prevent anemia (keep hematocrit (HCT) >25-30).
 * Avoid hypertension to prevent stressing the aneurysm.

• **Procedure Details:**

 * The surgeon cross-clamps above and below the aneurysm, opens the aorta, removes the diseased area, and replaces it with a graft.
 * Clamps are removed, and estimated blood loss (EBL) can be significant.
 * Note hemodynamic changes with clamping and unclamping.

• **Preoperative Preparation:**

 * Ensure a thorough cardiac workup; treat as a coronary artery disease (CAD) patient if not done.
 * Line and Monitoring:
   * Use the largest bore peripheral IVs possible (14G if possible).
   * Right internal jugular (IJ) line is preferred.
   * 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.
   * Blood transfusion tubing (2) should be prepared with normal saline (NSS).
   * Prepare a cell saver and warming blankets (2).

• **Induction and Intubation:**

 * Methods to avoid hypertension with direct laryngoscopy:
   * Consider adding Esmolol to induction to blunt BP spikes.
   * Use Remifentanil (start at 0.5-1 mcg/kg/min) 8 minutes before intubation.
   * High narcotic induction doses can be used, similar to heart cases.
   * Consider using a GlideScope to reduce stimulation.
 * Anesthesia:
   * General anesthesia with endotracheal tube (ETT).
   * Thoracic epidural is recommended; dose or start an infusion before incision.
   * Rapid Sequence Induction (RSI) is often used.
   * 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; they decrease 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 (usually 12.5-25 g) 30 minutes before cross-clamping.
 * Have Lasix available; 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 drop when unclamping.

• **Complications of Aortic Cross-Clamping:**

 * Increased risk of renal failure:
   * Preexisting renal disease
   * Cross-clamp time >30 minutes
   * Hypovolemia and decreased cardiac output without partial or complete bypass
 * Renal protection:
   * Mannitol (0.5-1.0 g/kg) is crucial before clamping.
   * Consider Lasix, Dopamine, and Fenoldopam based on surgeon's needs.
 * Paraplegia:
   * The anterior spinal cord is most prone to ischemia due to its single arterial supply.
   * Prolonged spinal cord ischemia occurs 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 directed by the surgeon.

• **Unclamping Effects:**

 * Reactive hyperemia occurs due to a drop in systemic vascular resistance (SVR) from metabolites in ischemic tissue.
 * Lactic acid causes vasodilation.
 * Consider using NaHCO3 if requested by the surgeon.
 * Increase minute ventilation to control acidosis; hypocarbia helps 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 patient’s head of bed (HOB) overnight.
   * Monitor 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 most susceptible to ischemia due to its single arterial supply.

• **Possible Complications:**

 * Ruptured aneurysm
 * Cardiac and pulmonary issues
 * Nerve damage causing pain or numbness in the legs
 * Intestinal or organ damage
 * Graft infection
 * Ureter injury
 * Incisional hernia
 * Spinal cord injury
 * Sexual dysfunction
 * Lower extremity paralysis
 * Death