AAA Anesthesia Management Dr. Beyer

Anesthetic Management of Abdominal Aortic Aneurysms Wilford Hall Medical Center Department of Anesthesiology Presented By: Jerry A. Beyer, M.D. Updated: 1/17/04 Anesthetic Goals  Minimize patient morbidity & mortality  Mortality has decreased rapidly since 1960’s  Elective AAA repair 30-day mortality rate  >25% in the mid-1960’s  1.8-8.4% mortality rate today  Advances in pre-op preparation and anesthetic management are largely responsible  Maximize surgical benefit  Achieve above goals in the most cost- effective manner Coexisting Diseases  Incidence of coexisting diseases in patients with aortic pathology presenting for surgery         Coronary artery disease Hypertension COPD Peripheral vascular disease Cerebrovascular disease DM Other aneurysms Chronic renal disease 66% 42% 23% 22% 14% 8% 4% 3% AAA Questions  What are the complications with an AAA?  Rupture is a feared problem. Half of all persons with     untreated AAA’s die of rupture within 5 years. AAA’s are the 13th leading cause of death in the U.S. Leaking AAA Embolization of clot within the aneurysm can occur when a piece of clot comes loose and travels further out in the arterial system Infection of aneurysms can occur from turbulent blood flow from the rough inner surface Spontaneous blockage of the aorta can also occur Definitions  Aortic Dissection: occurs when blood penetrates the aortic intima and forms an expanding hematoma within the vessel wall, usually separating the intima and media to create a so-called false lumen or “dissecting hematoma”  Aortic Aneurysm: involves dilation of all three layers of the vessel wall and has a highly different pathophysiology and implications for management  Dissecting Aneurysm: although commonly used, is often a misnomer Abdominal Vascular Anatomy AAA Questions  Where do aortic aneurysms tend to develop?  Aortic aneurysms can develop anywhere along the length of the aorta. The majority, however, are located along the abdominal aorta. Most (about 90%) AAA are infrarenal. About two-thirds of the AAA are not limited to just the aorta but extend into one or both of the iliac arteries. AAA Questions  What shape are most aortic aneurysms?  Most aortic aneurysms are fusiform. They are shaped like a spindle ("fusus" means spindle in Latin) with widening all around the circumference of the aorta. (Saccular aneurysms just involve a portion of the aortic wall with a localized out pocketing). AAA Questions  What's inside an aortic aneurysm?  The inside walls of aneurysms are often lined with a laminated blood clot that is layered like a piece of plywood. AAA Questions  Who is most likely to have an abdominal aortic aneurysm?  AAA’s are most common after age 60. Males are 4-5 times more likely than females to be affected. This means men over 60 are at highest risk to develop a AAA. Approximately 5% of men over age 60 develop a AAA.  Smokers are also at high risk, they are 7.6 times more likely than non-smokers to have a AAA. AAA Questions  What is the most common cause of aortic aneurysms?  The most common cause of aortic aneurysms is arteriosclerosis. At least 80% of aortic aneurysms are from arteriosclerosis. The arteriosclerosis can weaken the aortic wall and the pressure of the blood being pumped through the aorta causes expansion at the site of weakness. AAA Questions  What are other causes of aortic aneurysms?  Genetic: There is a familial tendency to aortic aneurysms. This tendency is at least in part genetic. Among the inheritable causes of aortic aneurysms are connective tissue disorders such as EhlersDanlos syndrome and Marfan's syndrome.  Post-traumatic: After physical trauma to the aorta.  Arteritis as occurs in Takayasu disease, giant cell arteritis, and relapsing polychondritis. AAA Questions  What are other causes of aortic aneurysms?  Congenital malformation of the aorta (aneurysms tend to develop just beyond the narrowing of a coarctation of the aorta; also with what is called a ductus diverticulum).  End-stage (tertiary) syphilis, which tends to affect the ascending aorta and arch of the aorta.  Mycotic (fungal) infection which may be associated with immunodeficiency, IV drug abuse, heart valve surgery. AAA Questions  What are the symptoms of an abdominal aortic aneurysm?  AAA’s may cause pain. The pain typically has a deep quality as if it is boring into the person. It is felt most prominently in the lower back region. The pain is usually steady but may be relieved by changing position. The person may also become aware of an abnormally prominent abdominal pulsation. However, many aneurysms are without symptoms. They may become large and even rupture without warning. AAA Questions  How is an abdominal aortic aneurysm diagnosed clinically?  Palpation of the abdomen may reveal the abnormally wide pulsation of the abdominal aorta. This is characteristically felt on both sides of the aorta which is in the midline. Note that even large aneurysms can be very difficult to detect on physical examination in overweight people. Aneurysms that are rapidly enlarging and on the verge of rupture are often tender. AAA Questions  What studies help in the diagnosis of AAA?  X-rays of the abdomen show calcium deposits in approximately 90% of cases.  Ultrasonography usually gives a clear picture of the extent and size of an aneurysm. Ultrasound has about 98% accuracy in measuring the size of the aneurysm.  CT scanning of the abdomen, particularly with contrast medium, can be highly accurate in determining the size and shape of the aneurysm. CT Scan of AAA With Contrast AAA Questions  What studies help in the diagnosis of AAA?  MRI scanning is similarly accurate compared to CT but is rarely necessary.  Abdominal angiography shows the origin of the major blood vessels arising from the aorta and reveals the size and extent of any aneurysm. Contrast angiography is especially useful if there is extension of the aneurysm above the renal arteries and in delineating a mural thrombus (a clot clinging to the wall of the aneurysm). AAA Questions  What are the primary factors involved in selecting patients for AAA repair?  Aneurysm rupture risk  Elective operative mortality risk  Life expectancy  Patient preference! AAA Questions  What is the natural history of AAA?  Annual rate of rupture by aneurysm diameter       <4 cm: 4-5 cm: 5-6 cm: 6-7 cm: 7-8 cm: >8 cm: 0% 0.5-5% 3-15% 10-20% 20-40% 30-50% AAA Rupture Risk Low Risk Diameter Expansion Smoking/COPD Family History Hypertension Aneurysm Shape <5 cm <0.3 cm/year None, mild No relatives Normal BP Fusiform Average Risk 5-6 cm 0.3-0.6 cm/year Moderate One relative Controlled Saccular High Risk >6 cm >0.6 cm/year Severe/Steroids Multiple relative Poorly Controlled Very Eccentric Wall Stress Gender Low (35 N/cm2) --------- Mdm. (40 N/cm2) Male High. (45 N/cm2) Female AAA Questions  Based upon the natural history of AAA, who do we generally consider for AAA repairs?  Repair considered for AAA >5.5 cm in males with “average” rupture risk aneurysms  Repair considered for AAA 4.5 – 5.0 cm in females and in patients with “high” rupture risk aneurysms  Repair considered for aneurysms 4.5 – 5.5 cm if the AAA is rapidly expanding (>1cm/year) or if symptoms develop  However, the decision to recommend surgical repair must be individualized in each case! AAA Questions  What is the 30-day mortality risk for open AAA repairs?  5.5% (average of 64 studies)   1-5% many referral-based series from individual centers of excellence 4-8% many recent population based series employing statewide or national databases AAA Questions  What are the primary independent risk factors for mortality following elective AAA repair? Risk Factor Creatinine >1.8 mg/dL CHF EKG Ischemia Pulmonary Dysfunction Older Age (per decade) Odds Ratio 3.3 2.3 2.2 1.9 1.5 95% CI 1.5-7.5 1.1-5.2 1.0-5.1 1.0-3.8 1.2-1.8 Female Gender 1.5 0.7-3.0 Operative Mortality Risk of Open AAA Repair Good Risk Age <70 Physically active No clinically overt cardiac disease No other significant co-morbidities Normal anatomy No adverse AAA characteristics Moderate Risk Age 70-80 Active Stable coronary disease; remote MI; EF>35% High Risk Age >80 Inactive, poor stamina Significant coronary disease; recent MI; frequent angina; CHF; EF<25% Mild COPD Adverse anatomy or AAA characteristics; Creatinine 2.0-3.0 Limiting COPD; dyspnea at rest; O2 dependent; FEV1<1 L/sec. Creatinine >3.0; Liver disease (Elevated PT, albumin <2) Mortality risk at least 5-10%, each comorbid condition adds approx. 3-5% risk Mortality risk 1-3% Mortality risk 3-7% AAA Questions  How are AAA’s repaired?  Open surgery consists of a midline or retroperitoneal approach to the aorta and sewing a synthetic graft inside the aneurysm.  More recently, "minimally invasive" (endovascular) procedures have been devised using stent grafts that can be guided to the site of the aneurysm.  The first stent graft was installed in 1991 by Dr. Juan Parodi in Argentina. Infrarenal AAA Infrarenal AAA Repaired With Gortex Graft AAA Questions  What complications can arise from open AAA repair?  Heart attacks during or after surgery  Kidney failure, which is most likely to occur when the aneurysm         is above the level of the renal arteries. Blood loss during surgery, which may necessitate a blood transfusion. Pneumonia and decreased pulmonary performance. Infection of the graft or the abdominal incision. Embolisms Rupture of the AAA in some rare instances Large bowel ischemia which may require a colostomy Impotence in men Paralysis AAA Questions  How are endovascular AAA repairs done?  A stent graft is a Dacron tube inside a collapsed metal-mesh cylinder. The stent, 15 cm long, is guided inside a long plastic capsule through the femoral artery to the lower aorta. Once the stent is in place, the holding capsule is removed. Activated by heat, the stent expands like a spring and becomes anchored to the artery wall. The by-passed aneurysm then is shielded from the blood flow and typically shrinks over time. AAA Questions  What are the advantages of endovascular AAA repairs?  About 60% less blood loss  Markedly shorter hospital stay (2-3 days vs. 7 days) and overall recovery period  Fewer patients require ICU (Intensive Care Unit) care  Patients usually able to consume solid food soon after surgery  Patients usually ambulatory the day after surgery AAA Questions  What potential complications do endovascular repairs have in common with open AAA repairs?  Heart attack  Kidney failure  Impotence in men  Bowel problems  Infection of the graft  Paralysis AAA Questions  What are the unique complications specifically related to endovascular repairs?  Difficulties with insertion may lead to urgent surgery and       potentially life-threatening complications Endoleaks, where blood continues to be present around the aneurysm, outside of the graft that now lines the aorta. This may happen immediately or even months after surgery, and it may be temporary or persistent. "Migration," or the graft slipping out of place Problems with the graft's overall durability Kinks or blockages in the graft Infection of the groin incisions Rupture of the AAA in some rare instances AAA Questions  Who should have an endovascular AAA repair opposed to an open repair?  Patients who are at increased risk for open repair  Possibly the preferred method for older, high-risk patients, and patients with “hostile” abdomens  Attempted endovascular repair on a patient with unsuitable anatomy markedly increases the risk of adverse outcomes, conversion to open repair, or AAA rupture  Patient preference is of great importance. Very important that the patient has true informed consent Humoral Factors That May Contribute to Organ Dysfunction After Aortic Occlusion          Acidosis Activation of renin-angiotensin system Activation of sympathetic nervous system Oxygen-free radicals Prostaglandins Platelet and neutrophil sequestration Complement activation Cytokine release Myocardial depressant factor Metabolic Changes With Aortic Cross-clamping  Decreased total body oxidative metabolism and O2 consumption  Supraceliac cross-clamp causes a 55% reduction in total body O2 consumption  Changes in SVO2 depend on method used to control BP during clamping   Arteriolar Dilators (SNP)increased SVO2 Venous Dilators (NTG)maintain oxygen extraction ratio and SVO2 Metabolic Changes With Aortic Cross-clamping  Conversion to anaerobic metabolism by the ischemic body mass distal to the cross-clamp  Exclusion of the liver and kidneys in high cross-clamps attenuates the elimination of lactic acid  Some lactate presumably reaching proximal circulation by way of collaterals  Role of lactate and other acidic metabolites in the development of hypotension after unclamping is somewhat controversial Blood Volume Redistribution During Aortic Cross-clamping  Blood volume redistribution during aortic cross-clamping. This scheme depicts the reason for the decrease in venous capacity, which results in blood volume redistribution from the vasculature distal to aortic occlusion to the vasculature proximal to aortic occlusion. If the aorta is occluded above the splanchnic system, the blood volume travels to the heart, increasing preload and blood volume in all organs and tissues proximal to the clamp. However, if the aorta is occluded below the splanchnic system, blood volume may shift into the splanchnic system or into the vasculature of other tissues proximal to the clamp. The distribution of this blood volume between the splanchnic and nonsplanchnic vasculature determines changes in preload. AoX - aortic cross-clamping; [arrow up] and [arrow down] - increase and decrease, respectively. Systemic Hemodynamic Response to Aortic Cross-clamping  Systemic hemodynamic response to aortic cross-clamping. Preload does not necessarily increase. If during infrarenal aortic cross-clamping blood volume shifts into the splanchnic vasculature, preload does not increase (Figure 1). AoX = aortic cross-clamping; Ao = aortic; R art = arterial resistance; [arrow up] and [arrow down] = increase and decrease, respectively. Systemic Hemodynamic Response to Aortic Unclamping  Systemic hemodynamic response to aortic unclamping. AoX = aortic cross-clamping; Cven venous capacitance; R art = arterial resistance; Rpv = pulmonary vascular resistance; [arrow up] and [arrow down] = increase and decrease, respectively. Effect of Level of Aortic Occlusion on Changes in Cardiovascular Variables % Change in Variable by Level of Aortic Occlusion CV Variable Mean arterial pressure Pulmonary capillary wedge pressure End-diastolic area End-systolic area Ejection fraction Abnormal wall motion (% of pt’s) New myocardial infarctions Supraceliac 54 38 28 69 -38 92 8 Suprarenalinfraceliac 5 10 2 10 -10 33 0 Infrarenal 2 0 9 11 -3 0 0 Risk Factors for Acute Renal Failure in AAA Repairs  Aortic cross-clamp time >30 minutes  Sustained intra-op & post-op hypotension  Prolonged reduction in cardiac output  Left ventricular dysfunction  Pre-op renal dysfunction  Advanced age Methods That May Be Useful for Renal Protection During AAA Repairs  Minimize aortic cross-clamp time  Maintain adequate renal perfusion if possible  Decreasing renal metabolic rate  Lasix, Cooling surface of kidneys Mannitol, Calcium channel blockers, Superoxide dismutase DA, Mannitol, Lasix, Fenoldepam, PGE-1  Decreasing reperfusion injury   Pharmacologic manipulation of renal BF  Does Good Intra-op Urine Output Predict Good Post-op Renal Function?  No correlation was found between mean intra-op hourly urine output and post-op changes in the plasma [Cr] in 137 patients undergoing AAA resection. (From Alpert RA, Roizen MF, Hamilton WK, et al. Intra-op urinary output does not predict post-op renal function in patient undergoing abdominal aortic revascularization. Surgery 1984;95:701-11 Spinal Cord Ischemia and Paraplegia After Aortic Surgery  Factors affecting the incidence of spinal cord injury resulting from surgeries involving aortic cross-clamping            Duration of aortic cross-clamp Extent of aortic disease Extent of surgical resection Presence of aortic dissection or rupture Sacrifice of critical intercostal arteries Method of managing proximal hypertension during crossclamping (vasodilators vs. shunts) Distal aortic pressure during cross-clamping CSF pressure and drainage  Spinal Cord PP= Distal Aortic Pressure – CSF pressure Patient’s age Degree and duration of intra-op & post-op hypotension Perioperative hyperglycemia Spinal Cord Ischemia and Paraplegia After Aortic Surgery  Methods that are potentially effective in reducing the frequency of spinal cord ischemic injury during aortic cross-clamping       Limited aortic cross-clamp time Perfusion of the distal aorta using fem-fem or atriofemoral bypass Drainage of CSF Reimplantation of intercostal and lumbar arteries Hypothermia (mild to profound, systemic or regional) Pharmacologic protection Sample Case  Patient is a 85kg 65 y/o male scheduled for a AAA repair that involves both iliac arteries.  PMHx: CAD, HTN, IDDM, CRI, Multiple prior TIA’s, Smoker (60 pack year Hx), BPH  PSHx: PTCA ’96 and ’02, Appy, popliteal distal bypass, TURP  Allergies: NKDA  Meds: Metoprolol, ASA, Ticlid, Insulin 70/30, Lisinopril, Clonidine, NTG patch, Flomax Sample Case  Is the patient ready for surgery?  Patient requests an epidural, what is your reply?  While placing the epidural you get blood through the needle, what do you do?  What monitors and lines will you use?  Do you need to talk with the blood bank?  Do you want to use the cell saver?  How will you induce this patient? Sample Case  The surgeon states that he/she will be placing an infrarenal aortic cross clamp in 10 minutes, how will you prepare?  After the aorta is clamped, do you expect to see a large increase in BP?  What will you do if the BP increases dramatically after cross-clamping?  The surgeon states that he/she will be unclamping the aorta in 10 minutes, how will you prepare? Sample Case  Is there anything the surgeon can do to make the discontinuation of the aortic crossclamping more hemodynamically stable?  You get an ABG and you notice the patient has a metabolic acidosis. Should you give NaHCO3?  The case is finished and you transfer the patient to the SICU intubated. Later that evening you receive a call from the surgeon stating that the patient can not move or feel his legs. What is your differential?