AA Aneurysm Open

Open Abdominal Aortic Aneurysm (AAA) Repair

Overview

• The open AAA repair procedure has become less common due to advancements in endovascular stent placements.
• Open procedures are associated with significant blood loss and complex surgical management.

Procedure Description

• An open AAA repair involves a midline abdominal incision to access and repair the aneurysm.
• Most open AAA procedures have been replaced by endovascular repair due to the latter's minimally invasive nature and reduced recovery times.
• Elective surgery is typically indicated for aneurysms exceeding 5 cm in diameter.
• Repair methods include:

 * **Straight Tube Graft**: Involves replacing the aneurysmal segment with a straight synthetic graft.
 * **Aorta to Bilateral Iliac Graft Replacement**: Replaces the aneurysmal segment with a graft extending from the aorta to both iliac arteries.

Symptoms

• AAAs are often asymptomatic and may be discovered incidentally during routine medical examinations.
• When symptomatic, patients may experience lumbar back pain, abdominal pain, or a pulsatile abdominal mass.
• Advanced symptoms may include:

 * Collapse
 * Shock
 * Coma

Imaging

• Diagnostic imaging options include:

 * **CT Scan**: Provides detailed cross-sectional images to assess aneurysm size and location.
 * **MRI**: Useful for evaluating complex cases and assessing soft tissue structures.
 * **X-ray**: Less commonly used but can provide preliminary information.
 * **Angiography**: Can visualize blood vessels and assess the aneurysm's relationship with major arteries.

• **CT Angiography** is increasingly preferred for its ability to detail aneurysm size, location (infra- or supra-renal), and the condition of major branches such as the inferior mesenteric artery.

Causes

• **Atherosclerosis**: The most common cause, involving the buildup of plaques in the aorta.
• **Genetic Disorders**: Conditions such as Marfan syndrome and Ehlers-Danlos syndrome.
• **Dissection**: Tear in the aortic wall leading to aneurysm formation.
• **Congenital Vasculitis**: Inflammation of blood vessels present from birth.
• **Infections**: Including syphilis and other rare causes.

Preoperative Tips

• **Patient Management**:

 * Maintain normothermia to prevent hypothermia-related complications.
 * Avoid tachycardia by managing heart rate.
 * Prevent anemia by maintaining a hematocrit (HCT) level >25-30%.
 * Prevent hypertension to reduce stress on the aneurysm.

Procedure Details

• The surgical technique involves:

 * **Cross-Clamping**: The aorta is clamped above and below the aneurysm to control blood flow.
 * **Aneurysm Removal**: The diseased portion of the aorta is excised.
 * **Graft Placement**: A synthetic graft is inserted to replace the removed section.
 * **Clamp Removal**: The clamps are removed, and blood flow is restored.

Preoperative Preparation

• Ensure thorough cardiac evaluation; treat as CAD patients if necessary.
• **Line and Monitoring**:

 * Use the largest bore peripheral IVs available (preferably 14G).
 * A right internal jugular (IJ) line is ideal for central access.
 * Consider a transesophageal echocardiogram (TEE) for continuous monitoring of left ventricular filling status.

• **Equipment Preparation**:

 * Fluid warmers (1-2)
 * Rapid transfusers or pressure bags
 * Blood transfusion tubing (2) with normal saline (NSS)
 * Cell saver
 * Warming blankets (2)

Induction and Intubation

• To minimize hypertension during intubation:

 * Add Esmolol to blunt blood pressure spikes.
 * Use Remifentanil (0.5-1 mcg/kg/min) 8 minutes before intubation.
 * High doses of narcotics may be employed for induction.
 * Utilize a GlideScope to reduce laryngoscopic stimulation.

• **Anesthesia**:

 * General anesthesia with endotracheal tube (ETT).
 * Thoracic epidural anesthesia may be administered before incision.
 * Rapid Sequence Induction (RSI) is often used due to the risk of aspiration.
 * Nasogastric (NG) tube placement is advised.

• **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
• High doses of narcotics can lead to rigidity; these doses help reduce the need for volatile anesthetics.

Pre-Induction

• **Priming Dose**: Use a non-depolarizing muscle relaxant or succinylcholine for RSI.
• **Fluid Management**:

 * Connect fluids to the warmer immediately.
 * Use a Bair Hugger for warming.
 * Administer a 200-500 cc fluid bolus before induction.

Induction to Pre-Clamp Period Goals

• **Avoid Hypertension**: Prevent aneurysm rupture due to high blood pressure.
• **Mannitol Administration**: Administer 0.5 g/kg (typically 12.5-25 g) 30 minutes before cross-clamping.
• **Lasix**: Have available for managing fluid balance as instructed by the surgeon.

Preparation for Aortic Cross-Clamping

• **Medications**:

 * Ensure availability of nitroglycerin and/or Milrinone.

• **Monitoring**:

 * Check ionized calcium (Ca) levels.

• **Volume Management**:

 * Maintain adequate volume and prepare to manage blood pressure drops during unclamping.

Complications of Aortic Cross-Clamping

• **Renal Failure**:

 * Risk factors include preexisting renal disease, cross-clamp duration >30 minutes, and hypovolemia without bypass.
 * **Renal Protection**:
   * Mannitol (0.5-1.0 g/kg) is crucial.
   * Consider Lasix, Dopamine, and Fenoldopam based on surgical needs.

• **Paraplegia**:

 * The anterior spinal cord is particularly vulnerable due to its single arterial supply.
 * Prolonged ischemia can result from cross-clamping >30-45 minutes or perioperative hypotension.

Methods to Prevent BP Drops with Unclamping

• **Anesthetic Management**:

 * Decrease anesthetic depth.
 * Maintain hypervolemia while clamped.

• **Vascular Management**:

 * Infuse Neosynephrine before clamp removal.
 * Gradual unclamping is preferred to mitigate hemodynamic changes.

Unclamping Effects

• **Reactive Hyperemia**: Caused by a drop in systemic vascular resistance (SVR) from ischemic tissue metabolites.
• **Lactic Acid**: Dilates blood vessels; some surgeons may request sodium bicarbonate (NaHCO3).
• **Ventilation Management**:

 * Increase minute ventilation to control acidosis.
 * Hypocarbia helps constrict vessels and redirect blood flow to ischemic tissues distal to the clamp.

Late Operative and Postoperative Considerations

• **Edema Management**:

 * Facial, scalp, and airway edema are common.
 * Delay extubation until edema subsides; elevate the head of the bed (HOB) overnight.

• **Fluid Shifts**:

 * Postoperative fluid shifts can cause pulmonary issues, delaying extubation despite apparent readiness.

Spinal Cord Blood Supply

• **Sources**:

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

• The anterior spinal cord is most prone 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**
• **Ureter Injury**
• **Incisional Hernia**
• **Spinal Cord Injury**
• **Sexual Dysfunction**
• **Lower Extremity Paralysis**
• **Death**