General Anesthesia Management of Suspected Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAA) are the most common form of aneurysms. This case report outlines events that occurred during an open inguinal hernia repair on a patient that had an unknown AAA. Proper anesthetic management of at risk patients and patients with AAAs can greatly improve the safety of induction, maintenance, emergence, and postoperative care. AAA is a weakening of the aortic wall, which results in progressive dilatation that can eventually rupture. The precise pathophysiology is unclear, but they are believed to develop from lipid deposition within the aortic adventitia. Dissection occurs when the damaged tunica interna allows blood to flow into the tunica media, thus creating a false channel that can dissect and rupture under the high aortic arch pressure. Without immediate repair, rupture is usually fatal and is therefore a medical emergency.1 Risk factors for developing an AAA include: male gender, increasing age, smoking, hyperlipidemia, hypertension, and genetics.2

1 GENERAL ANESTHESIA MANAGEMENT OF SUSPECTED ABDOMINAL AORTIC ANEURYSM by Sarah Palmieri, RN, BSN A capstone project submitted in partial fulfillment of the requirement for the degree of Master of Science in Nurse Anesthesia Westminster College Salt Lake City, Utah December 2014 2 Keywords: Abdominal aortic aneurysm (AAA), general anesthesia, medical management, preoperative evaluation, dissection Abstract Abdominal aortic aneurysms (AAA) are the most common form of aneurysms. This case report outlines events that occurred during an open inguinal hernia repair on a patient that had an unknown AAA. Proper anesthetic management of at risk patients and patients with AAAs can greatly improve the safety of induction, maintenance, emergence, and postoperative care. AAA is a weakening of the aortic wall, which results in progressive dilatation that can eventually rupture. The precise pathophysiology is unclear, but they are believed to develop from lipid deposition within the aortic adventitia. Dissection occurs when the damaged tunica interna allows blood to flow into the tunica media, thus creating a false channel that can dissect and rupture under the high aortic arch pressure. Without immediate repair, rupture is usually fatal and is therefore a medical emergency.1 Risk factors for developing an AAA include: male gender, increasing age, smoking, hyperlipidemia, hypertension, and genetics.2 3 Case Report A 57 year old, 62-kilogram male veteran presented for a left open inguinal hernia repair. The patient's medical history included chronic obstructive pulmonary disease (COPD) with a FEV1/FVC ratio of 0.46%, a 45-pack year smoking history, hypertension, hyperlipidemia, and gastro esophageal reflux disease. The patient's medications included aspirin, atorvastatin, lisinopril, and nicotine. The patient also had an exercise stress test that showed 1.5 mm ST segment depression at peak exercise that resolved immediately in the recovery phase. The patient did not experience angina and had adequate exercise tolerance so the patient was cleared for general anesthesia. All laboratory values were within normal limits, EKG showed sinus tachycardia with a heart rate of 102 and right atrial enlargement, and an allergy to metoprolol was noted. Based on the American Society of Anesthesiologists (ASA) guidelines, the patient was designated a physical status classification of III. The patient was given intravenous (IV) versed 2 mg preoperatively and was transported to the operating room. The patient moved himself to the operating room table, oxygen was administered by face mask at 10 L/min, and standard monitors, including a five lead EKG, were applied to the patient. Prior to induction, the patient's vital signs were 130/80 blood pressure, 80 heart rate, 100% oxygen saturation, and ST segment in leads II and V5 were 0.2 and 0.1 mm, respectively. A smooth IV induction of fentanyl 50 mcg, lidocaine 100 mg, and propofol 120 mg was given and a laryngeal mask airway (LMA) #4 was placed without difficulty. While the circulating nurse was prepping the patient, a large abdominal pulsatile mass was noted and assessed and a possible AAA came into question. The surgeon was 4 notified of the findings and he wished to proceed with the case. Anesthesia was maintained with an end tidal of sevoflurane at 1.5%, blood pressure was within 20% of the patient's baseline, and heart rate was maintained in sinus rhythm at 80 beats/min with no ST segment changes throughout the case. Ondansetron 4 mg and fentanyl 250 mcg were given during the case. At the end of the case, the LMA was removed with the patient in stage III and spontaneously breathing, an oral airway was placed, and the patient was brought to the post anesthesia recovery unit (PACU) with no complications. Postoperatively, the patient had a computerized tomography (CT) scan, which revealed an 8.1 cm suprarenal AAA. The patient was transferred to a regional medical center to be further evaluated and scheduled for surgery to repair his AAA. Discussion The incidence of AAA is increasing.1 While the exact reason for the increase is unclear, possible causes include an increased incidence of obesity, atherosclerosis, and improved detection and diagnostic screening modalities.2 Data suggest that risk of rupture is very low for AAAs less than 4 cm in diameter, but it dramatically increases for AAAs 5 cm in diameter or greater. Surgical intervention is recommended for AAAs 5.5 cm or greater in diameter.3 Ruptured AAAs are responsible for 15,000 deaths per year in the United States with mortality ranging from 35% to 94% .3-4 The 5-year mortality rate for individuals with untreated AAAs is 81%, and the 10 year mortality rate is 100%. Therefore, early detection, medical treatment, and elective surgical intervention can be lifesaving.3 5 The American College of Cardiology/American Heart Association clinical practice guidelines have helped to define strength of evidence to support medical management for AAAs less than 5 cm in diameter. Level A evidence (from large randomized trials) indicates that observation of small aneurysms in men is safe up to a size of 5.5 cm and that propranolol does not inhibit aneurysm expansion. Level B evidence (from small randomized trials) suggests that treatment with roxithromycin or doxycycline will decrease the rate of aneurysm expansion by inhibiting matrix metalloproteinase (MMP)-9 levels, which degrades collagens and extracellular matrix proteins. Level B and C evidence (one or more studies with moderate to severe limitations) suggests that statins may inhibit aneurysm expansion.4 It is important for anesthesia practitioners to know risk factors and current medical therapy for AAAs in order to ensure their patient's condition is fully optimized prior to surgery. Patients presenting for surgery, even if unrelated to their AAA, need a thorough preoperative assessment to determine if any essential testing is necessary to identify interventions that may improve outcomes and to minimize perioperative mortality and morbidity.5 Preoperative testing most often involves identifying and characterizing cardiac, respiratory, renal, endocrine, atherosclerotic, and peripheral arterial occlusive disease.6 Cardiac evaluations of patients with AAAs scheduled for noncardiac surgery are imperative and should include a 12-lead ECG and a stress test with cardiac clearance if indicated. In this particular case, the patient had multiple risk factors for not only an AAA, but also cardiac disease. Even though the AAA was undiagnosed prior to surgery, he still had the proper preoperative cardiac assessment and clearance. Oral beta-blockers should also be 6 initiated to all patients with intermediate to high cardiac risk several weeks prior to surgery and should be titrated to a target heart rate of 60 to 70 beats/min to prevent tachycardia and ischemia. As smoking is a major risk factor for the development of AAA, many of these patients have chronic respiratory disease. A respiratory assessment, including chest radiograph, pulmonary function testing, and blood gas analysis, will help guide anesthesia providers to create a comprehensive plan for perioperative ventilation.6 This patient had a long history of smoking and severe COPD. Therefore, an LMA was chosen for the case to allow the patient to breathe spontaneously for the short duration of surgery. When patients have a known or suspected AAA, the core aim of intraoperative anesthetic management is ensuring hemodynamic stability and maintaining normothermia.5 Minimum standard monitors should be placed and a five-lead ECG is more sensitive in detecting myocardial ischemia.3,5 Even though this patient had an unknown AAA, 5 lead ECG monitoring was used due to his high risk for cardiac disease. Arterial lines may also be indicated for longer procedures and when fluctuations in blood pressure are anticipated.3 Induction should be carried out in a manner in which the patient's hemodynamics remain as close to baseline as possible.3,5 For maintenance of general anesthesia, patients who have poor myocardial performance may develop hypotension when exposed to moderate or severe myocardial depression caused by inhalation agents. It may be prudent to administer lower concentrations of inhalation agents (<1 MAC) and greater amounts of narcotics.3 Emergence should focus on preventing bucking and coughing which can cause hypertension, increased abdominal pressure, and tachycardia. Postoperative care should 7 focus on adequate analgesia and nausea control to prevent tachycardia and hypertension from pain and increased intra-abdominal pressure from vomiting. This patient had a large AAA that was at high risk for rupture, which if not managed cautiously could have ended in catastrophe. Because he had the proper preoperative assessment and had a higher risk for cardiac disease, he was treated with caution. In conclusion, patients who present for surgery with AAAs or suspected AAAs usually also present with intermediate to high-risk cardiac disease. Therefore, precautions to prevent adverse cardiac events should be the same for preventing rupture of AAAs; including proper preoperative assessment and testing and maintaining hemodynamic stability during induction, maintenance of anesthesia, and emergence. 8 References 1. Woodrow, P. Abdominal aortic aneurysms: clinical features, treatment and care. Nurs Stand. 2011; 25(50): 50-58. 2. Elisha, S. Case Studies in Nurse Anesthesia. Sandbury, MA: Jones and Bartlett Publishers, LLC. 2011: 301-309. 3. Nagelhout, J. Plaus, K. Nurse Anesthesia. 4th ed. St. Louis, MI: Saunders Elsevier. 2010: 530-531. 4. Baxter, T. Terrin, M. Dalman, R. Medical management of small abdominal aortic aneurysms. Circulation. 2008. 117(14): 1883-1889. 5. Al-Hashimi, M., Thompson, J. Anaesthesia for elective open abdominal aortic aneurysm repair. Cont Educ Anaesth Crit Care Pain. 2013: 1-5. 6. Elisha, S., Nagelhout, J., Heiner, J., Gabot, M. Anesthetic case management for endovascular aortic aneurysm repair. AANA J. 2014; 82(2): 145-152. Mentor: James Stimpson, CRNA, DNP [e-mail]