Acs0603 Pulsatile Abdominal Mass


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Acs0603 Pulsatile Abdominal Mass

  1. 1. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 1 3 PULSATILE ABDOMINAL MASS Timothy A. Schaub, M.D., and Gilbert R. Upchurch, Jr., M.D., F.A.C.S. Assessment of a Pulsatile Abdominal Mass When a pulsatile abdominal mass is found on physical examina- sentation of a ruptured AAA is a triad comprising hypotension, tion, the location of the mass and the symptoms associated with it back or abdominal pain, and a pulsatile abdominal mass. become essential clinical clues. The underlying condition may Unfortunately, this traditional presentation occurs less than half of range in severity from benign to life threatening. Further evalua- the time. In a study of 116 patients with ruptured AAAs, 45% tion is imperative; in certain clinical settings, immediate transport were hypotensive, 72% had pain, and 83% had a pulsatile abdom- to the operating room is indicated. Because inappropriate treat- inal mass.9 Accordingly, it is essential not to be lulled into a false ment can be catastrophic, it is important to base one’s approach sense of security when evaluating a hemodynamically stable to assessment and management of a pulsatile abdominal mass as patient with a pulsatile abdominal mass. Although a ruptured firmly as possible on the available evidence. In what follows, a clin- AAA is an uncommon event in a patient with a stable blood pres- ical approach based on relevant evidence is outlined. sure and no abdominal pain, the absence of these symptoms does not rule out the possibility. Symptomatic or ruptured aneurysms can mimic many other Clinical Evaluation acute medical conditions and therefore are part of multiple differ- The most feared cause of ential diagnoses. The following conditions all may be confused a pulsatile abdominal mass with ruptured AAAs: (1) perforated viscus, (2) mesenteric is an abdominal aortic aneu- ischemia, (3) strangulated hernia, (4) ruptured visceral artery rysm (AAA). In the United aneurysm, (5) acute cholecystitis, (6) acute pancreatitis, (7) rup- States, AAAs are present in tured appendix, (8) ruptured necrotic hepatobiliary cancer, (9) 3% to 9% of the population, lymphoma, and (10) diverticular abscess. Fortunately, misdiagno- resulting in approximately sis of a ruptured AAA is rare. Moreover, most patients who do 15,000 fatalities each year.1 undergo an operation for a misdiagnosis either benefit from or at In 1999, AAAs were the 15th leading cause of death in the United States.2 Deaths from AAA declined in subsequent years,3 but with the overall aging of the U.S. population, this disease remains a major threat to public health. PRESENTATION Asymptomatic AAAs are considerably more common than symp- tomatic AAAs and are often discovered on abdominal or pelvic scans done for other indications (e.g., back pain or renal cysts) rather than on physical examination.4,5 Plain films of the lumbar region, routine- ly obtained in patients with back pain, may show a calcified shell of the aorta [see Figure 1]. In one review of 31 patients with surgically proven ruptured AAAs, 65% had calcification of the aneurysm that was visible on a plain abdominal radiograph.6 In addition, ultra- sonography and computed tomography are nearly 100% sensitive in detecting AAAs.7 In elderly patients, evaluation of the aorta should be routinely included in abdominal ultrasonography; scanning of the aorta adds, on average, only 43 seconds to the study.8 If an AAA is unexpectedly found, either the patient is followed or the aneurysm is repaired, depending on the clinical situation and the size of the aneurysm (see below). Ruptured AAAs, on the other hand, give rise to pronounced Figure 1 Shown is a plain film of the abdomen (anterior-poste- symptoms, and the patient’s condition may range from hemody- rior view) in an elderly woman who presented complaining of namic stability to class IV shock.When the patient is unstable, fur- vague abdominal pain. The patient was found to have an AAA, ther workup is unnecessary and emergency repair is indicated.The diagnosed by plain film and believed to be approximately 5 cm in situation is less clear when the patient is stable.The traditional pre- size. Arrows follow the course of calcium outlining her aorta.
  2. 2. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 2 Patient presents with pulsatile abdominal mass Perform clinical evaluation. • Presenting signs and symptoms: presence or absence of pain, location, associated symptoms. • Medical and surgical history: risk factors for development or rupture of AAA, previous operations, other surgical disease. • Physical examination: vital signs, abdominal palpation (safe but poor at screening and detection). Assess stability of patient. Patient is unstable Assume ruptured aneurysm until proven otherwise. Perform emergency repair. Standard of care is open repair, but endovascular repair may be possible in certain circumstances. No aneurysm is found Search for other possible causes of complaints. If aortic diameter is normal and patient > 60 yr, no further screening is indicated. If aorta is enlarged, rescreen in 5–8 yr or if symptoms develop. Pain is absent Base subsequent treatment on aneurysm size. Aneurysm ≥ 5.5 cm Aneurysm < 5.5 cm Risk of rupture in 1 yr is greater than risk of operative Risk of rupture in 1 yr is less repair. than risk of operative repair. Consider elective AAA repair [see Figure 4]. Optimize medical management. Perform follow-up US in 6 mo. If aneurysm grows by > 0.4 cm in 12 mo or becomes symptomatic, offer repair. Educate patient to signs/symptoms of AAA development and rupture.
  3. 3. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 3 Assessment of a Pulsatile Abdominal Mass Patient is stable Perform US to determine whether aneurysm is present. Differentiate aneurysm from arteriomegaly or arterial ectasia. Aneurysm is found Assess degree of patient discomfort, especially in back, abdomen, legs, or testicles. Pain is present Base subsequent treatment on aneurysm size. Aneurysm < 5.5 cm Aneurysm ≥ 5.5 cm Look for other possible causes of complaints, but maintain high index of suspicion for ruptured AAA. Risk of rupture is high. Look for factors increasing risk of rupture (e.g., female sex, smoking, ↓FEV1, ↑BP). Determine renal function, and perform imaging to look for rupture. Creatinine < 2 mg/dl: CT scan. If patient is allergic to dye, use steroid prep if time allows. Other cause is present No other cause is present Creatinine ≥ 2 mg/dl or patient allergic to dye but no time for steroid prep: MRA. Risk of rupture is low. Risk of rupture is moderate to high. No rupture is found Rupture is found Risk of rupture is moderate. Continue Perform emergency repair. to search for cause of pain. Consider elective AAA repair [see Figure 5].
  4. 4. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 4 Table 1 Risk Factors Associated with The patient’s surgical history is also crucial, particularly in that AAA Development it can shorten the differential diagnosis at presentation by ruling out disease processes (e.g., appendicitis and cholecystitis). In Factors Positively Associated with Factors Negatively Associated with addition, the nature and extent of any previous abdominal proce- Development of AAA Development of AAA dures may influence the surgeon’s operative approach to the AAA repair.When a pulsatile abdominal mass is discovered in a patient Increased age Female sex who previously underwent open repair of an AAA, it is important Increased height Black race to remember that anastomotic pseudoaneurysms27 or synchro- Coronary artery disease Presence of diabetes nous lesions (e.g., iliac artery aneurysms28) can occur at sites Any atherosclerosis High cholesterol levels remote from the previous repair. Hypertension Patients who have undergone endovascular AAA repair may Smoking also present with symptoms in the presence [see Figure 2] or Male sex absence of an endoleak. In a 2002 review, most ruptures after Family history (first-degree relative) endovascular AAA repair occurred with type I endoleaks in the tube endograft configuration.29 This clinical scenario is well described and can present as a pulsatile abdominal mass.29-31 least are not harmed by the operation, which should alleviate The risk of rupture after endovascular repair is small,29 but the some potential concerns about taking an aggressive approach to a long-term outcome of this relatively new approach remains to be suspected ruptured AAA.10 Conversely, AAAs can mimic other determined. Overall mortality after rupture in patients with pre- disease processes: in one study, nearly one in five patients with vious endografts approaches 50%, and the operative mortality is 41%.29 symptomatic AAAs in an emergency department were originally diagnosed as having nephroureterolithiasis.11 Patients who have PHYSICAL EXAMINATION urologic symptoms but whose urinalysis is normal may benefit Before the advent of modern radiologic tests, the abdominal from an AAA workup; radiologic evidence of ureteric involvement examination was the key to detecting an AAA. Gray’s Anatomy, is present in as many as 71% of AAAs.12 first published in 1858, noted that AAAs formed “a pulsating HISTORY tumour, that presents itself in the left hypochondriac or epigas- tric regions.”32 The abdominal aorta begins at the level of the The medical history may be helpful in determining the patient’s diaphragm and the 12th thoracic vertebra and runs in the retro- level of risk for an AAA. Even in the absence of clinical symptoms, peritoneal space just anterior to and slightly to the left of the knowledge of the risk factors may facilitate earlier diagnosis. The spine. At approximately the level of the umbilicus and the 4th Aneurysm Detection and Management Veterans Affairs lumbar vertebra, it bifurcates into the right and left common Cooperative Study Group trial (commonly referred to as the iliac arteries. In young, thin individuals, the abdominal aorta ADAM trial) found a number of factors to be associated with runs close to the surface of the abdomen and thus can often be increased risk for AAA: advanced age, greater height, coronary palpated during a normal physical examination. Palpation of an artery disease (CAD), atherosclerosis, high cholesterol levels, hy- AAA is safe and has not been reported to precipitate rupture. A pertension, and, in particular, smoking.13 The risk was lower in 1997 report found, however, that only 31% of the AAAs studied women, African Americans, and diabetic patients. AAAs occur almost exclusively in the elderly and are rarely seen in patients younger than 50 years. In a 2001 study, the mean age of patients undergoing repair for AAAs in the United States was 72 years.14 Male patients outnumber female by a fac- tor of 4 to 6, depending on the study cited.14-18 Family members of AAA patients are also at significant risk: 12% to 19% of per- sons undergoing AAA repair have a first-degree relative with an AAA.19-21 Accordingly, screening is recommended in all men and women older than 50 years who have a family history of AAA.22 AAAs are over seven times more likely to develop in smokers than in nonsmokers, with the duration of smoking, rather than total number of cigarettes smoked, being the key variable [see Table 1].23 Of particular importance is identification of risk factors for rupture. The United Kingdom Small Aneurysm (UKSA) trial reported 103 AAA ruptures in 2,257 patients over a period of 7 years, with an annual rupture rate of 2.2%.23 The factors found to be significantly and independently associated with an increased risk of rupture were female sex, a larger initial AAA diameter, a lower forced expiratory volume in 1 second (FEV1), a current smoking habit, and a higher mean blood pressure.23,24 Figure 2 Shown is a CT scan of a patient who presented to the Women are two to four times more likely to experience rupture emergency room with increasing back pain 2 years after an of an AAA than men are.24,25 AAAs in cardiac and abdominal endovascular AAA. The patient was found to have a type II transplant patients also appear to have high expansion and rup- endoleak (arrow), which was treated with coil embolization of a ture rates.26 lumbar artery.
  5. 5. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 5 Large Right Common studies have been published comparing ultrasonography, the cur- Iliac Artery Aneurysm rently preferred screening method, with physical examination.37,38 One such study found that abdominal palpation had a poor (14.7%) positive predictive value for detecting AAAs greater than 3.5 cm in diameter.38 At present, with the wide availability of ultra- sound screening, physical examination is playing a smaller role in AAA detection. Although most AAAs appear supraumbilically, not all pulsatile abdominal masses appear there. In some patients, the abdominal aorta becomes more tortuous and elongated with age. As a result, an AAA may appear infraumbilically or to one side of the abdomen or the other. The common iliac arteries may become aneurysmal and palpable in one of the lower abdominal quadrants as well [see Figure 3].39 Another indication that an AAA may exist is the presence of a femoral or popliteal artery aneurysm on physical examination. A patient with a femoral artery aneurysm has an 85% chance of hav- ing a concomitant AAA, and a patient with a popliteal artery aneurysm has a 62% chance.40,41 Conversely, in a study evaluating 251 patients with documented AAAs, 14% had either a femoral or a popliteal artery aneurysm.42 There is a significant male predom- inance, for unknown reasons.15,42,43 Figure 3 Shown is a CT scan of a patient presenting with an abdominal mass who, in addition to having a small AAA, was Indications for found to have a large right common iliac artery aneurysm, Emergency Repair palpable in the right lower quadrant of the abdomen. versus Further Workup PATIENT IS UNSTABLE at a major teaching institution were initially detected by physical If a patient presents with examination.33 Nonaneurysmal common iliac arteries also are a pulsatile abdominal mass often difficult to palpate, even in thin individuals. and is medically unstable, There are several methods of conducting a proper physical no further study or workup examination of the abdominal aorta. Our preferred approach is necessary: the diagnosis, resembles that of Lederle and Simel34: until proved otherwise, is a ruptured AAA.The only cure for a rup- tured AAA is an emergency operation. Indeed, when all patients 1. Have the patient lie supine with the knees raised. Encourage experiencing a ruptured AAA are taken into account, including the patient to relax the abdomen. A relaxed abdomen is often both those who arrive at the hospital alive and those who do not, obtainable with passive exhalation after a deep inhalation. overall mortality is still between 77% and 94%, with over 50% of 2. Beginning a few centimeters cephalad to the umbilicus and patients expiring before reaching the hospital.44,45 Most ruptured just to the left of the midline, palpate deeply for the pulsation AAAs leak into the left retroperitoneum, which may serve to con- of the aorta. fine the bleeding.46 However, AAAs that rupture freely into the 3. To confirm that the aorta is being palpated, place both hands abdominal cavity usually result in death, either at home or en route on the abdomen with the palms down in such a way that the to the hospital. Even if the patient makes it to the OR, the expect- pulsation is between the tips of the index fingers. The index ed mortality exceeds 50%47 (though values as low as 15% and as fingers should move apart with each heartbeat. high as 90% have been noted48). Mortality after a ruptured AAA 4. Once it is certain that the index fingers are bracketing the has declined since the middle of the 20th century by approxi- aorta, estimate the diameter of the aorta by measuring the dis- mately 3.5% per decade; however, the most recent estimate, for tance between the fingertips, taking into account the thickness the year 2000, is still 41%.48 of the overlying tissue. Although some physicians suggest that patients with predictably Unfortunately, physical examination is not very accurate in high morbidity and mortality from a ruptured AAA may not bene- detecting AAAs: in one study, approximately 62% of known AAAs fit from attempted repair,49 most would still maintain that even in were missed.35 Whether an AAA is detectable on physical exami- this population, this presentation necessitates operative interven- nation alone depends primarily on the size of the aneurysm. AAAs tion.50 The high cost of repair and the substantial operative mortal- more than 5 cm in diameter are detectable on physical examina- ity notwithstanding, surgical repair of ruptured AAAs appears to tion in 76% of the population, whereas those 3 to 3.9 cm in diam- be cost-effective in comparison with no intervention.51 Thus, eter are detectable in only 29%. Palpation of an AAA 3.0 cm in cost should not be considered in the management of patients diameter or larger has a positive predictive value of only 43%.34 In with AAAs. addition, detection of AAAs is significantly limited by truncal obe- Open repair of ruptured AAAs is the current standard of care [see sity.36,37 Thus, physical examination is clearly insufficient for ruling 6:11 Repair of Infrarenal Abdominal Aortic Aneurysms].There is evidence, out or screening for AAAs.34,36 however, that endovascular approaches may come to play a more sig- In the past, it was considered important to measure the abdom- nificant role. A 2003 study described endovascular repair of 29 rup- inal aorta accurately by means of physical examination. Several tured AAAs and reported a mortality of only 11%.52
  6. 6. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 6 PATIENT IS STABLE is an enlargement of an artery by an amount that is less than 50% If a patient with a pul- of the normal diameter.61 satile abdominal mass is The main limitations of ultrasonography are that (1) the results medically stable, further are highly technician dependent and (2) resolution is dependent on workup is called for. As not- body habitus and intestinal gas.46 Another limitation is that it is unre- ed, ultrasound imaging is liable in detecting rupture [see Figure 4]. Because ultrasonography significantly more accurate does not provide an accurate picture of the aorta proximal to the re- in detecting an AAA than nal arteries and because it is subject to the limitations already men- physical examination alone tioned, it cannot be routinely used to differentiate a ruptured AAA is.38 Duplex ultrasonogra- from a symptomatic intact AAA. If ultrasonography is inconclusive phy is used extensively as a primary screening tool for evaluating the in the evaluation of a palpable abdominal mass, then either CT or size of an abdominal aorta because of certain advantages it possesses MRA (see below) is the next step [see Table 2]. over other, more extensive modalities, such as CT, magnetic reso- nance angiography (MRA), and conventional angiography. Its main Management advantages are that (1) it is noninvasive, (2) it is relatively inexpen- sive, (3) it does not require exposure to radiation, (4) it is portable, STABLE PATIENT WITH- and (5) it is as reliable as the other modalities in determining aortic OUT ANEURYSM anterior-posterior (AP) diameter. Ultrasound-derived measure- ments are reproducible to within 3 to 5 mm,53 and the interobserver If ultrasonography indi- variability is less than 5 mm in 84% of AP measurements.54 In about cates that a patient with a 75% of cases, ultrasonography underestimates the size of the aorta. pulsatile abdominal mass A comparison study found that AAA diameter measurements were does not have an aneurysm, consistently and significantly larger with CT than with ultrasound the risk of aortic or com- (5.69 ± 0.89 cm versus 4.74 ± 0.91 cm).55 It appears that when radi- mon iliac artery rupture is very low. Consequently, if symptoms ologists take more care with their measurements (e.g., by using mag- (e.g., abdominal pain) persist, another causative condition must be nifying glasses and calipers), the results correlate better.56 considered. Ultrasonographic measurement of the infrarenal aorta and the If arteriomegaly is found to be the cause of the pulsatile abdom- common iliac arteries has been evaluated in patients with no inal mass and there are no symptoms of occlusion, then no specif- known vascular disease. In one study of patients older than 50 ic treatment is required. Routine ultrasonographic follow-up is years (the age group in which abdominal aortic and iliac artery indicated because the risk of rupture still applies as the aorta con- aneurysms are most common), the aorta measured 1.68 ± 0.29 tinues to expand. In one study, an aneurysm was present in 1.6% cm in men and 1.46 ± 0.19 cm in women (P < 0.001).57 The of aortas with arteriomegaly.62 If aortic ectasia (by most standards, common iliac arteries measured 1.01 ± 0.20 cm in men and 0.92 an aorta measuring 2.5 to 3 cm) is found to be the cause, follow- ± 0.13 cm in women. An aneurysm is commonly defined as a per- up ultrasonography in 5 to 8 years is recommended.61,63 It has manent localized or focal expansion of an artery to 1.5 times its been suggested that for a 65-year-old man with a normal aortic expected diameter.46 Thus, an infrarenal AAA would be consid- diameter (defined as less than 2.6 cm), the risk that a significant- ered to be approximately 3 cm in diameter. It must be remem- ly dilated aneurysm will develop during the remainder of his life is bered, however, that infrarenal aortic diameter is affected by essentially zero.64 The distinction between a normal and an ectat- height, age, race, body surface area, and sex.58-60 An aneurysm ic aorta remains something of a gray area, and the preferred fol- should be differentiated from arteriomegaly and from arterial or low-up period remains controversial. In general, ectatic infrarenal aortic ectasia. Arteriomegaly is a diffuse enlargement of an artery aortas expand slowly and are not associated with rupture.61 by an amount that is at least 50% of the normal diameter; ectasia In the ADAM trial, independent and significant predictors of a new aneurysm on follow-up ultrasonography included (1) current smoking (odds ratio, 3.09), (2) coexisting CAD (1.81), and, in a separate model with composite variables, (3) any atherosclerosis (1.97).63 Accordingly, when a patient has any of these risk factors, a lower threshold for follow-up ultrasonography and a shorter period between examinations may be practical. STABLE PATIENT WITH ANEURYSM Once the diagnosis of an aneurysm is made in a sta- ble patient, the subsequent course of action is deter- mined by the clinical pre- sentation and the size of the Graft Rupture AAA pulsatile abdominal mass. It must be emphasized that if the patient becomes hemodynamically unstable at any point during evaluation, operative intervention is necessary—unless the Figure 4 Depicted is rare ultrasonographic documentation of a patient has a terminal condition or has indicated that nothing fur- ruptured AAA proximal to an old aortic tube graft. ther should be done to prolong life.
  7. 7. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 7 Table 2 Advantages and Disadvantages of Aortic Imaging Techniques Imaging Modality Advantages Disadvantages Noninvasive Highly technician dependent Relatively inexpensive Resolution dependent on body habitus and intestinal gas Does not require radiation exposure Unreliable in detecting AAA rupture Ultrasonography Portable Achieves poor visualization of aorta proximal to renal arteries Comparable in reliability to other modalities in determining and of iliac arteries aortic AP diameter Yields highly precise measurements Requires radiation exposure Defines proximal and distal extent of AAAs precisely Requires iodinated contrast Delineates anatomy of iliac arteries Expensive CT Evaluates AAA wall integrity (notes location and amount of calcification and thrombus) Effective at discovering venous anomalies, retroperitoneal blood, aortic dissection, inflammatory aneurysms, and other intra-abdominal pathology and anomalies Comparable to CT in preoperative evaluation Not widely available Uses nonnephrotoxic contrast agent (gadolinium) Very expensive MRA Highly sensitive and specific in detecting stenoses of May cause claustrophobia in select patients splanchnic, renal, and iliac arteries Requires longer scan time Contraindicated in patients with certain metal foreign bodies More expensive than spiral CT Superior in evaluating intraluminal characteristics of aorta Angiography Associated with multiple risks (e.g., infection, arterial throm- Superior in determining visceral branch involvement bosis, distal embolization, groin hematoma, local arterial Superior in delineating variations in vascular anatomy dissection, and risk of renal failure secondary to contrast) If the patient is experiencing no discomfort and is otherwise sta- fourfold. When the increased tangential stress exceeds the elastic ble, the risk of active rupture can be considered extremely low. If, capacity of the wall, rupture occurs. Elastic tissue in the abdomi- however, the patient is experiencing significant pain or discomfort, nal aorta becomes attenuated as a result of age and of certain especially in the back, the abdomen, the legs, or the testicles, AAA acquired and genetic factors; thus, a modest degree of expansion rupture should remain a strong diagnostic possibility. over time is not uncommon. An abnormal rate of expansion is usually considered to be 5 mm/yr or greater. Documentation of an Pain Is Absent accelerated aneurysm growth rate should cause the surgeon to A patient with a pulsatile give serious consideration to operative intervention[see 6:11 Repair abdominal mass who has a of Infrarenal Abdominal Aortic Aneurysms].46 known AAA and who is Multiple studies have examined aneurysm diameter, usually indi- hemodynamically stable cated by the greatest AP diameter of the aorta, as a risk factor for without complaints of pain rupture; several studies have documented that increased AP diame- should be further catego- ter is in fact the greatest predictor of rupture. This conclusion has rized on the basis of the size been challenged, however, by studies using three-dimensional CT of the aneurysm. This cate- scanning to evaluate wall stress via a mathematical technique called gorization is traditionally finite element analysis.65-67 In these studies, maximal wall stress was based on the physics of an expanding aneurysm and on the asso- a better predictor of rupture than maximal AP diameter was. For ex- ciation between increased risk of rupture and increased aneurysm ample, one patient with a ruptured 4.8 cm aneurysm had a wall size. The key considerations in these patients are (1) whether the stress equivalent to that of a patient with an electively repaired 6.3 risk associated with AAA repair exceeds the risk of rupture in a cm AAA.66 Future management of AAAs may be based on actual given period and (2) what other factors are present that may affect wall stress in addition to maximum AP diameter. this decision. In a 2001 study addressing open operative repair of intact AAAs, increased mortality was associated with increased patient Indications for operative intervention The physics of age, female sex, cerebral vascular occlusive disease, preoperative aneurysm expansion and rupture are probably best understood via renal insufficiency, and the presence of more than three comorbid the law of Laplace,8 according to which the tangential stress (τ) conditions before operation.14 In the UKSA trial, the 30-day mor- placed on a cylinder filled with fluid (e.g., a blood vessel) is deter- tality in patients undergoing elective open AAA repair was 5.8%.68 mined by the equation The point at which the risk of elective repair became acceptable in relation to the risk of rupture with medical management and ser- τ = Pr/δ ial ultrasonographic follow-up was an aneurysm diameter of 5.5 where P is the pressure (dynes/cm2) exerted by the fluid, r is the cm. The investigators suggested that in patients with AAAs less internal radius (cm) of the cylinder, and δ is the thickness (cm) of than 5.5 cm in diameter, medical management is the best course the cylinder wall. When the aorta expands, its radius increases of action.The operative mortality reported in this study is consid- while its wall thickness decreases; thus, there is a geometric ered high, in that many single-center series have documented mor- increase in tangential stress. As an aneurysm grows from 2 cm in talities of 1% to 3% after open repair of intact AAAs.69-71 The diameter to 4 cm, tangential pressure increases not twofold but ADAM investigators also found that survival was not improved
  8. 8. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 8 when AAAs smaller than 5.5 cm were repaired electively, even if a repair.47,76 Accordingly, older patients with multiple comorbidi- low operative mortality was associated with the procedure.70 ties may be preferentially offered endovascular AAA approach in Hospital volume may have a significant effect on patient outcome place of open repair.30 The surgeon must, however, consider the after elective AAA repair. A 2002 study found that mortality after possibility that any operative intervention will be too risky in this this procedure was 56% higher at low-volume hospitals than at high- population or that other interventions must be carried out before volume hospitals.72 Moreover, mortality after repair of an intact AAA AAA repair can be attempted. These issues should be addressed exhibited a ninefold variation that could be attributed to hospital vol- via appropriate preoperative evaluation [see Figure 5]. ume, sex, and age alone.Thus, when a patient is being evaluated for AAA repair, it is important to take into account not only the size of Small AAAs (< 5.5 the aneurysm but also age, sex, comorbidities, and hospital volume. cm): medical manage- In turn, more than half of the effect of hospital volume on operative ment and follow-up mortality in elective AAA repair appears to be mediated by surgeon When a patient with stable volume.73 Surgeon specialty also appears to affect operative mortali- vital signs and no abdomi- ty after elective AAA repair.74 nal pain is diagnosed as Given the various possible complicating factors, it is clear that having a small AAA (i.e., < no single aortic diameter can serve as a definitive indication for 5.5 cm), serial ultrasonog- operative intervention in every patient. It is well known that rup- raphy and optimization of tures can occur unpredictably at aneurysm diameters smaller than medical management are 5.5 cm.75 Therefore, the timing of AAA repair must be individual- indicated.77,78 Small AAAs usually do not rupture.24,79 Most small ized, with the 5.5 cm figure serving as a general guideline in the AAAs continue to grow, however, typically by 0.2 to 0.4 cm in counseling of patients. diameter per year.70,77,80 Small AAAs can also expand rapidly with Advanced age, terminal conditions, and various end-of-life unpredictable frequency. A rapidly expanding AAA is at high risk issues may deter patients from wishing to proceed with operative for rupture, regardless of how small it may be.68,70,80,81 intervention. In addition, severe coexisting diseases significantly Many risk factors have been identified that may affect the risk affect the morbidity and mortality associated with AAA of small aneurysm expansion and rupture. For example, one study suggested that diastolic hypertension and chronic obstructive pul- monary disease (COPD) increased the risk that a small AAA would rupture,75 whereas another found advanced age, severe car- Patient has known AAA ≥ 5.5 cm or meets diac disease, previous stroke, and a history of cigarette smoking to other criteria for elective repair be risk factors for rapid expansion.80 AAAs smaller than 5.5 cm Initiate preoperative evaluation. may rupture more frequently in women than in men. A 2002 • Assess level of cardiac risk, and determine need study found that in almost one quarter of women with ruptured for and extent of preoperative cardiac workup. AAAs, the diameter of the aneurysm was less than 5.5 cm at the • Look for vascular comorbidities (peripheral, coronary, time of rupture.44 Currently, the safest and easiest method of fol- renal, or carotid artery disease). lowing small AAAs is serial ultrasonography.11,82 When the diame- • Optimize management of other medical conditions ter of an AAA approaches 5.5 cm, a more detailed study (e.g., CT (e.g., COPD, renal dysfunction, or diabetes). or MRA) is indicated if repair is being considered.46 Over the past several decades, the number of AAAs (especially smaller AAAs) detected has increased.83 This increase has been attributed to two causes: (1) increased serendipitous detection in Renal function is impaired Renal function is normal the course of scans done for other indications and (2) the “gray- ing” of the population.46,83 With the potential advent of a screen- Perform MRA with gadolinium Perform spiral CT with I.V. ing program for AAA in the near future, thanks to growing evi- and breath-hold technique. contrast. dence that such screening is cost-effective,22,84 it is likely that even more AAAs will be detected yearly. This prospect raises an inter- esting issue, in that at present, the only proven treatment for AAAs is operative; current medical therapy is notably limited. Clearly, Consider aortography if indicated. Indications include there is a need to find medical therapies that can prevent, reduce, • aneurysm involving suprarenal aorta • possible or stabilize the growth of AAAs.To that end, a better understand- renovascular abnormalities • possible mesenteric ischemia • severe occlusion of iliac, femoral, or ing of how AAAs develop is essential. lower-limb arteries • femoral or popliteal aneurysm. Basic science studies have helped elucidate the etiology of AAAs in greater detail. In particular, current research is focusing on (1) evaluating the role various proteolytic enzymes, such as matrix metalloproteinases (MMPs), play in processes involving the struc- Elective repair is not Elective repair is tural elements in the aortic wall; (2) investigating the importance indicated indicated of the immune system, specifically the macrophage, in the devel- Determine whether open opment of AAAs; (3) determining how hemodynamic and biome- or endovascular AAA chanical stress affects aortic wall remodeling; and (4) identifying repair is more appropriate. molecular genetic variables that contribute to AAA development.85 Proteolytic enzymes are currently being evaluated as potential Figure 5 Shown is an algorithm that may be used to guide the predictors of the course of AAA growth.86 Doxycycline, which preoperative workup of a patient who is to undergo elective AAA decreases MMPs in animal aneurysm models independently of its repair. antibiotic properties, was evaluated in a prospective, randomized
  9. 9. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 9 phase II trial published in 2002.87 Although it did not exert a sig- that statins reduce the production of MMPs in the wall of AAAs.98 nificant effect on aneurysm growth over the short study period (6 The role of lipid-lowering medications in the treatment of AAAs re- months), doxycycline significantly reduced serum levels of MMP- mains to be clarified. Elevated levels of homocysteine in the blood 9, a gelatinase that plays a central role in degrading elastin and col- are a recognized independent risk factor for atherosclerosis, and a lagen in the abdominal aortic wall. Few side effects were noted, study of AAA patients has found significantly higher levels of plasma and most of them were easily reversible. These findings, though homocysteine, along with lower levels of vitamin B12.99 Given this not conclusive, suggest that the use of doxycycline may one day finding, and the possible role of vitamin B12 in homocysteine regu- prove to be a viable medical means of slowing AAA growth. lation, use of supplemental vitamins may theoretically modify AAA Control of hypertension would seem to be an obvious approach progression.99 to medical control of aneurysms, in that hypertension is a significant Smoking is an independent risk factor for AAA develop- risk factor for both development and rupture of AAAs.24,75,79,88 To ment,63,88 expansion,80,96 and rupture.24 Current smokers are 7.6 this end, various antihypertensive agents, including beta blockers, times more likely to have an AAA than nonsmokers are, and ex- calcium channel blockers, and angiotensin-converting enzyme smokers are three times more likely to have an AAA.23 The dura- (ACE) inhibitors, have been evaluated in patients with AAAs.23 The tion of smoking is the key variable13,23,88: the relative risk of AAA results have been somewhat equivocal. development is increased by 4% for each year of smoking.23 The Beta blockers have been shown to reduce the expansion rate of ADAM trial noted that a longer interval since the cessation of large AAAs (≥ 5 cm) but not that of smaller AAAs.89,90 Some of smoking was significantly associated with a decreased risk of AAA them (e.g., propranolol) may be poorly tolerated at high doses.90 formation13; however, the decline in risk appears to be slow.23 The In addition, beta blockers are often contraindicated in patients UKSA trial showed that former smokers were at lower risk for with severe COPD, though as many as 11% of COPD patients death from AAA repair than current smokers were.68 A 2002 have AAAs.24 A 1999 study suggested that receiving a calcium study found that there was an independent association between channel blocker was an independent risk factor for the presence of smoking and high-grade tissue inflammation in AAAs,100 lend- an AAA (odds ratio, 2.6).23 The same study also noted, however, ing support to the idea that smoking is an initiating event in AAA that patients receiving calcium channel blockers had stiffer aortic formation. walls. ACE inhibitors, in contrast, were associated with decreased At present, intriguing possibilities notwithstanding, few defini- aortic wall stiffness and increased collagen turnover, whereas tive recommendations can be made regarding the use of medical diuretics and beta blockers had no effect on aortic wall stiffness. therapy to reduce AAA growth. The indications for perioperative None of the medications examined were found to affect the beta blockade are primarily cardioprotective. Administration of growth rate of AAAs. Aortic stiffness appears to be an important antihypertensives may be beneficial from a practical perspective, variable: increased aortic wall distensibility is associated with an but current level I data supporting this practice are lacking. If an increased risk of AAA rupture, and it is almost as powerful a pre- antihypertensive is given, the choice of agent should be based on associated clinical data (e.g., the presence of coexisting medical dictor of rupture as actual AAA diameter.91 conditions, such as angina or renal insufficiency, whose manage- A link between COPD and AAAs is suggested by the presence ment must be optimized). The administration of lipid-lowering of a common development pathway: both conditions are associat- drugs to patients with AAAs also requires further study, though ed with elastin breakdown and smoking. A 1999 study argued, the utility of such agents in the presence of CAD, which is found however, that the strong association between AAAs and COPD in almost 50% of AAA patients,101 is well documented, and long- was most likely attributable to coexisting cardiovascular disease term statin use after successful AAA surgery has been associated and medications.24 In this study, the average annual aortic diame- with reduced mortality (both all-cause and cardiovascular).102 ter expansion rate was 4.7 mm in patients who used oral steroids Finally, smoking cessation is clearly mandatory. but only 2.6 mm in those who did not. The use of beta-adrener- gic agonists was also a positive predictor of aneurysm expansion. Pain Is Present Thus, oral steroids and beta agonists must be used cautiously in When a patient present- COPD patients who have AAAs. If an AAA patient must use one ing with a pulsatile abdom- of these medications, close follow-up is indicated to monitor the inal mass is hemodynami- expansion rate of the aneurysm. cally stable but complains Atherosclerosis is associated with AAAs but is currently believed of pain in the abdomen, the to be a secondary phenomenon, with inflammation and matrix-de- back, the testicles, or the grading enzymes being the primary factors in AAA development.92 femoral region, the index Lipoprotein (a) has been found to be an independent risk factor for of suspicion must be high atherosclerosis and is elevated in patients with AAAs independently for a symptomatic or rup- of the patients’ cardiovascular risk factors or the extent of atheroscle- tured AAA. Other possible causes should be considered as well. As rosis.93 It seems reasonable that lowering lipid levels would decrease noted (see above), many abdominal processes may mimic an the development of atherosclerosis of the abdominal aorta.This is a AAA; however, it is important that recognition of an AAA not be potentially important effect because patients with small atheroscle- delayed unduly, because the length of the interval between the rotic AAAs often experience thrombotic complications involving the onset of symptoms and subsequent diagnosis and operation can lower extremities.94 Levels of apolipoprotein-AI and high-density have a direct bearing on overall survival.The size of the aneurysm, lipoproteins have also been found to be significantly lower in patients as determined by ultrasonography, is helpful for identifying with AAAs.95 Overall, however, lipids appear to play only a minor patients at highest risk for rupture. Ultrasonography is sometimes role in AAA progression.96 An animal study suggested that regres- able to detect a ruptured aneurysm, but it should not be relied on sion of plaque by lowering serum lipid levels after atherosclerotic to rule out rupture. In one study, ultrasonography demonstrated aneurysm formation may result in increased aneurysm dilation in extraluminal blood in only 4% of ruptured AAAs in the emer- the abdominal aorta.97 A subsequent study, however, demonstrated gency department.103
  10. 10. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 10 cial. Optimization of perioperative medications is also important for maximizing risk reduction. Finally, adequate preoperative imaging is essential.The decision regarding which type of repair is most appropriate in an AAA patient should be based on the pre- operative evaluation. Coronary Artery Disease Before AAA repair, it is important to identify patients who are at high risk for a perioperative cardiac event and who need a pre- operative cardiac intervention. It is also important to identify patients who are at low risk, so that they are not subjected to unneeded testing. A report from the American College of Cardiology/American Heart Association (ACC/AHA) Task Force on Practice Guidelines provided useful guidelines for pre- Table 3 ACC/AHA Guidelines for Preoperative Cardiac Evaluation in Patients Undergoing Elective High-Risk Vascular Procedures110 Figure 6 Shown is a CT scan of a patient presenting with a pul- satile abdominal mass and dull, aching back pain. The scan was If yes, without recurrence of signs or symp- obtained before contrast administration and demonstrates free 1. Revascularization in the toms of ischemia, then further cardiac test- past 5 years? ing is not indicated. Proceed with surgery. extravasation of blood into the retroperitoneum. If no, go to 2. If yes, findings are favorable on adequate test 2. Coronary evaluation in without onset of new symptoms, or symp- In stable patients with AAAs larger than 5.5 cm who are expe- the past 2 years? toms change, proceed with surgery. If no or riencing pain, either CT or MRA may be used to detect AAA rup- findings are unfavorable, go to 3. ture; the choice typically depends on the patient’s medical history Major clinical predictors include [see Table 2]. After ultrasound evaluation, if an aneurysm smaller Unstable coronary syndromes than 5.5 cm was found and no associated risk factors for rupture Decompensated CHF were identified, a search for other possible causes of the pain is rea- 3. Major clinical predictor Significant arrhythmias sonable, provided that it is performed expeditiously. of risk present? Severe valvular disease If no other cause for the pain can be found, possible rupture Presence of these predictors cancels or delays intervention until they are ameliorat- should remain a prime consideration, and the next step in evalua- ed. Implement medical management. tion—namely, spiral CT or MRA—should be implemented. Consider coronary angiography. Go to 4. Missing or delaying the diagnosis of a ruptured AAA can be dis- Intermediate clinical predictors include astrous. If retroperitoneal blood is noted, then the study need not Mild angina pectoris be completed, and the patient should be taken to the OR [see Prior MI Figure 6]. If the aneurysm is not ruptured, repair should be under- Compensated or prior CHF taken urgently (i.e., within the next 24 hours), with the patient’s Diabetes mellitus medical condition optimized to the extent possible[see 6:11 Repair Renal insufficiency of Infrarenal Abdominal Aortic Aneurysms]. Precipitous repairs of 4. Intermediate clinical When these indicators are present, perfor- predictor of risk present? mance of noninvasive testing in AAA repair nonruptured symptomatic AAAs have an operative mortality five candidates is indicated, especially if 2 or times that of elective repairs,104 for reasons yet unknown. more are present. If, after noninvasive test- ing, patient is determined to be low risk, continue with operation. If risk is high, con- Preoperative Evaluation of Nonemergency AAA sider coronary angiography. If no predictors are present, go to 5. Repair Candidates Minor clinical predictors include Evaluation of a patient before elective AAA repair begins with Advanced age assessment of the expected benefit of repair in relation to the esti- Abnormal ECG mated risk. If the decision is made to operate, the history and the Nonsinus rhythm physical examination should be completed as described earlier [see Low functional capacity Clinical Evaluation, above]. The clinical findings, in conjunction 5. Minor or no clinical Previous stroke with ECG and routine laboratory test results, provide most of the predictors present? Uncontrolled systemic hypertension information that is needed for evaluating a patient’s candidacy for If minor or no clinical predictors are present and patient can attain 4 METs or more, pro- AAA repair. ceed with surgery. Consider noninvasive testing when < 4 METs are attained, espe- COMORBID CONDITIONS cially in presence of multiple minor clinical predictors; then go to 6. CAD is common in patients with AAAs and is the leading cause of early and late mortality after AAA repair.105 Renal insufficiency, 6. Risk after noninvasive Low risk: proceed with operation. COPD, and diabetes mellitus also may influence morbidity and testing? High risk: consider coronary angiography. mortality after AAA repair. Accordingly, when any of these disease ACC—American College of Cardiology AHA—American Heart Association entities is present, further evaluation before repair may be benefi- CHF—congestive heart failure MET—metabolic equivalent MI—myocardial infarction
  11. 11. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 11 Table 4 Estimated Energy Required sports), are assessed.The energy required to perform an activity is quantified in terms of metabolic equivalents (METs).The number for Various Activities110,137 of METs of which a patient is capable directly correlates with the ability to perform specific tasks [see Table 4]. Patients who are Activity Level METs* Sample Activities unable to attain 4 METs are considered to be at high risk for peri- Eating; playing a musical instrument; operative cardiac events and long-term complications. Finally, the Mild 1–3 walking at 2 mph; getting dressed; inherent risk of the procedure to be performed is evaluated. AAA golfing (with cart) repair is considered high-risk. Calisthenics without weights; climbing a The original ACC/AHA recommendations for supplemental Moderate 3–5 flight of stairs; housework; golfing preoperative testing were updated in a 2002 statement.110 (without cart); running a short distance Currently, it is generally agreed that preoperative testing should be Chopping wood; strenuous sports such limited to patients in whom the results have the potential to alter Vigorous 4–12+ as football, basketball, singles tennis, the current course of management.The following noninvasive tests karate, or jogging (10 min mile or faster) may be considered. *1 MET = 3.5 ml . kg-1 . min-1 oxygen uptake. 1. 12-lead ECG. This test is recommended. Certain ECG abnormalities are clinical predictors of perioperative and long-term cardiac risks in patients undergoing high-risk operative cardiac evaluation in patients undergoing noncardiac operative procedures [see Table 5]. vascular surgery [see Table 3], with the express goal of limiting the 2. Transthoracic echocardiography to evaluate resting left ven- use of perioperative cardiac procedures in patients at moderate tricular function. This test is indicated in the presence of and high risk for complications.106 Use of these guidelines and heart failure. If it was previously done and demonstrated permutations thereof has proved both safe and effective at reduc- severe left ventricular dysfunction, repeat evaluation is ing resource use and overall costs.107-109 According to the unnecessary. It may be of benefit in patients with prior heart ACC/AHA guidelines, patients needing urgent or elective AAA failure and those with dyspnea of unknown etiology. repair are stratified first by whether coronary revascularization Routine use is not beneficial in the absence of heart failure. was done within the past 5 years. If so, and symptoms have not 3. Exercise or pharmacologic stress testing. Such testing is recurred, the patient is cleared for operation. If the patient never useful for diagnosing CAD in patients with an intermediate underwent coronary revascularization, underwent revasculariza- pretest probability of CAD, but its value is less well estab- tion more than 5 years before, or is experiencing recurrent symp- lished in those with a high or low pretest probability. It is a toms or signs of cardiac ischemia, further evaluation of clinical good prognosticator for patients with suspected or proven predictors is necessary. CAD who are undergoing initial evaluation, for patients Clinical predictors of major perioperative cardiovascular risk— whose clinical disposition has changed significantly, and for defined as myocardial infarction (MI), congestive heart failure, or those who have experienced an acute coronary syndrome. death—may be divided into three categories106: major, intermedi- Stress testing is also recommended for demonstrating the ate, and minor.The presence of a major predictor requires that the presence of myocardial ischemia before coronary revascu- symptom or disease be managed appropriately before nonemer- larization and for evaluating the efficacy of medical therapy. gency surgery.The presence of an intermediate predictor is associ- It may be useful in patients whose subjective assessment of ated with an increased risk of perioperative cardiac complications exercise tolerance is unreliable and in whom evaluation in and requires that current status be fully investigated.The presence terms of METs is therefore impossible. Less clear are the of a minor predictor is indicative of cardiovascular disease but has following indications for stress testing: (1) diagnosis of not been shown to independently increase the risk of perioperative CAD in patients who have resting ST depression of less cardiovascular complications. than 1 mm, are on digitalis, or show evidence of left ven- Once the clinical predictors have been evaluated, additional pre- tricular hypertrophy on ECG, and (2) detection of resteno- dictive factors, involving the patient’s ability to perform various sis in high-risk patients who have recently (i.e., within the activities (ranging from minor activities of daily living to strenuous past few months) undergone percutaneous transluminal coronary angioplasty (PTCA). Exercise stress testing should not be done (1) to diagnose patients with ECG find- Table 5 ECG Findings as Clinical Predictors of ings that would prevent adequate assessment, (2) in patients with severe comorbidities that would preclude Increased Perioperative Cardiovascular Risk136 coronary revascularization, (3) for routine screening of Major predictors asymptomatic patients, or (4) to evaluate young patients High-grade atrioventricular block with isolated ectopic beats on ECG. Symptomatic ventricular arrhythmias in the presence of underlying heart disease Coronary angiography, if indicated, may be performed next. Supraventricular arrhythmias with uncontrolled ventricular rate Current indications in patients scheduled to undergo AAA repair Intermediate predictor include (1) high-risk status after noninvasive testing, (2) continued Pathologic Q wave indicating previous myocardial infarction angina despite adequate medical therapy, (3) unstable angina, and Minor predictors (4) an equivocal result on noninvasive testing in high-risk patients. Left ventricular hypertrophy Coronary angiography may be beneficial in patients with multiple Left bundle-branch block intermediate clinical risk factors. If noninvasive testing reveals ST-T abnormalities moderate-sized to large areas of ischemia in a patient without high- Rhythm other than sinus (e.g., atrial fibrillation) risk criteria and a lower left ventricular ejection fraction, or if test- ing is nondiagnostic in a patient at intermediate clinical risk, coro-
  12. 12. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 12 nary angiography may also be indicated. The indication for coro- sively, before AAA repair, or in the course of the repair.46 nary angiography is more controversial in patients who have expe- rienced a perioperative MI. Coronary angiography is not indicat- Diabetes Mellitus ed in patients who are asymptomatic after coronary revasculariza- Whether diabetes mellitus is truly an independent risk factor for tion and who are capable of at least 7 METs. morbidity or mortality after aortic surgery is controversial. Several Both coronary artery bypass grafting (CABG) and PTCA have studies have shown that the risk of death is not increased in diabetic been employed to treat CAD before AAA repair. CABG is usual- patients, but the risk of perioperative complications may be.119-121 ly done in this setting only if it has been decided that the patient Most of these studies had small study groups and thus lacked the needs the intervention regardless of the current status of the statistical power needed to demonstrate that diabetes had a signifi- abdominal aorta. Such patients have a high-risk coronary anatomy cant influence. A 2002 study of patients at VA medical centers who and have a long-term prognosis that may improve if coronary underwent major vascular procedures found that diabetic patients revascularization is performed. The combination of AAA repair were indeed at higher risk for death and cardiovascular complica- and CABG has been evaluated, and there are some data to sup- tions.122 When examined separately, however, patients undergoing port its use in highly select patients.111,112 AAA repair did not have higher rates of cardiovascular complica- To date, no controlled trials have evaluated the efficacy of PTCA tions or death than patients undergoing other procedures. against that of medical therapy before noncardiac aortic surgery. PERIOPERATIVE MEDICATIONS Although some small observational studies have indicated a low cardiac mortality when preoperative PTCA is performed in this Multiple studies have addressed optimization of medical man- setting, complications after PTCA are not infrequent and include agement in patients with AAAs. Beta blockers, alpha2-adrenergic the need for emergency CABG. One retrospective review found agonists, nitrates, and calcium channel blockers have all been eval- uated in this setting. Other agents used in the treatment of cardio- that patients who underwent prophylactic PTCA before noncar- vascular disease (e.g., aspirin) have not been specifically evaluated diac surgery were twice as likely to have an adverse cardiac out- in regard to reduction of perioperative cardiac complications in come as healthy patients were.113 This study did not control for patients undergoing aortic surgery.123 CAD severity, medical management, or comorbidities. A later A review of the literature supporting perioperative beta block- study concluded that both CABG and PTCA offered only mod- ade was published in 2002.124 Five randomized, controlled trials est protection against adverse cardiac events after major arterial were evaluated, and the results suggested that this measure had a surgery (CABG, < 5 years; PTCA, < 2 years).114 General indica- beneficial effect on perioperative cardiac morbidity. The number tions for PTCA use are outlined in the 2001 revision of the 1993 needed to treat to prevent one MI was 2.5 to 6.7 patients; the ACC/AHA Guidelines for Percutaneous Coronary Intervention.115 number needed to treat to produce a significant effect on cardiac It is recommended that patients wait at least 2 weeks—preferably, or all-cause mortality was 3.2 to 8.3 patients. All but one of the 4 to 6 weeks—after PTCA before undergoing AAA repair; this studies reported a significant reduction in postoperative MIs after delay allows the plaque to stabilize after stenting and permits full beta blocker use, with the effect being most obvious in high-risk treatment with antiplatelet agents. patients. Thus, it appears that perioperative beta blockade is most Pulmonary Disease likely beneficial for patients at high risk for cardiac events who are to undergo AAA repair, unless it is otherwise contraindicated (e.g., Between 7% and 11% of patients with COPD have an AAA.24 by COPD). The therapeutic goal should be to attain a resting Traditionally, when such patients are to undergo AAA repair, heart rate of 60 beats/min or lower before operation.123 room air arterial blood gas values are determined and pulmonary Alpha2-adrenergic agonists (e.g., clonidine) have not been shown function tests performed to assess the extent of COPD. If COPD to reduce MI rates or mortality from cardiac causes. In one study, is severe, formal pulmonary consultation may be necessary for mivazerol did not exert a significant overall effect in patients under- prediction of short- and long-term prognoses and optimization of going major vascular or orthopedic procedures but was associated treatment. Several studies have reported that COPD is an inde- with a significant reduction in MI rates and mortality from cardiac pendent predictor of operative mortality.14,71,116 A 2001 study of causes in patients with known CAD.125 Therefore, when periopera- Veterans Affairs (VA) patients, however, found no significant cor- tive beta blockade is contraindicated, administration of alpha2-adren- relation between the presence of COPD and increased operative ergic agonists may be of benefit in high-risk patients. mortality (though morbidity was notably higher).117 A 2003 study To date, studies evaluating the perioperative use of nitroglycerin evaluating morbidity and mortality after AAA repair in patients and diltiazem to lower the risk of cardiac events have not found with COPD showed that the preoperative factors significantly this practice to be beneficial in this regard. It may be best to associated with a poor outcome included (1) suboptimal COPD reserve these agents for patients who need them for angina or management, as evidenced by fewer inhalers used, (2) a lower pre- ischemic symptoms and for those who have myocardial ischemia operative hematocrit, (3) preoperative renal insufficiency, and (4) after operation.123 the presence of CAD.118 It is noteworthy that abnormal preopera- It is widely accepted that aspirin is beneficial in reducing the tive pulmonary function tests and arterial blood gas values were risks associated with CAD.126 Its continued use throughout the not predictive of a poor outcome. Thus, COPD by itself is not a perioperative period is controversial, however, as is the use of contraindication to AAA repair. clopidogrel, because of the potential complications associated with Renal Failure decreased platelet function. Indications for the use of these antiplatelet agents may be patient dependent.127 Traditionally, Preoperative renal insufficiency [see 8:7 Renal Failure] is known aspirin is discontinued at least 1 week before aortic surgery. to be a risk factor for a poor outcome after AAA repair14,71,117,118 and thus should be evaluated and corrected if possible. In certain FURTHER IMAGING patients with AAAs, renal artery stenosis may be contributing to The main methods used to evaluate the aortic anatomy before impaired renal function; if so, it may be corrected either noninva- AAA repair are ultrasonography, CT, MRA, and aortography.
  13. 13. © 2004 WebMD Inc. All rights reserved. ACS Surgery: Principles and Practice 6 VASCULAR SYSTEM 3 PULSATILE ABDOMINAL MASS — 13 Which method is employed in a given situation depends largely on dissection, inflammatory aneurysms, and other intra-abdomi- the clinical presentation, the history, the comorbid conditions pres- nal pathologic conditions and anomalies (e.g., horseshoe kid- ent, and the availability of equipment and expertise. Each has its ney). Therefore, CT is the study of choice for excluding AAA advantages and disadvantages [see Table 2]. rupture in stable but symptomatic patients.1,53,128 Thin-cut heli- cal/spiral CT arteriography with multiplanar reconstruction is a Ultrasonography recommended study for evaluating patients before endovascu- Further ultrasonographic evaluation of the aortic anatomy, if lar AAA repair; CT arteriography is also preferred for deter- indicated, is performed in accordance with the approach mining whether an endoleak has occurred after endovascular described earlier [see Patient Is Stable, above]. AAA repair.129 In the near future, ultrasonography may sup- plant CT for these applications. CT Scanning The main drawbacks associated with CT scanning are (1) radi- The current standard for preoperative imaging of AAAs is con- ation exposure and (2) the requirement for iodinated contrast trast-enhanced CT scanning.This modality is more accurate than material, which cannot be used in patients with dye allergies or aortography at measuring AAA diameter and determining the renal insufficiency. In addition, spiral CT with three-dimensional presence of rupture.53 With spiral CT, it is possible to obtain a reconstruction is relatively expensive at present. Allergic reactions three-dimensional view of the abdominal aorta. CT scanning is to the contrast agent can usually be prevented by giving a standard highly accurate, with measurements reproducible to within 2 mm. steroid-diphenhydramine preparation. Alternatively, CT scanning Measurement variations as great as 5 mm are sometimes seen, may be done without contrast to determine whether there is a however, occurring 9% to 17% of the time.54,56 Such variations large retroperitoneal hematoma, which would be indirectly sug- may be reduced by standardizing measurements, reducing the gestive of a ruptured AAA. If the patient has renal insufficiency, number of radiologists reading the images, and using calipers and MRA may be more appropriate. magnification for greater accuracy.56 The advantages of CT over ultrasonography include (1) MRA more precise definition of the proximal and distal extent of In patients with renal insufficiency who are scheduled for AAA AAAs, (2) better delineation of the iliac arterial anatomy, (3) repair, MRA with gadolinium and the breath-hold technique may the ability to evaluate AAA wall integrity, noting the location be the preoperative study of choice; it is comparable to CT scan- and amount of calcification within vessel walls, and (4) the abil- ning in evaluating elective AAA repair candidates [see Figure ity to identify venous anomalies, retroperitoneal blood, aortic 7].86,130 The main advantages of MRA are that (1) it does not require the use of nephrotoxic agents or radiation and (2) it is highly sensitive and specific in detecting stenoses of the splanch- nic, renal, and iliac arteries.85 Its main drawbacks are that (1) it is not widely available, (2) it is expensive, (3) it may cause claustro- phobia in select patients, and (4) it takes longer to perform than CT scanning. MRA is contraindicated in patients with pacemak- ers, metallic foreign bodies in the eye, cochlear implants, and cer- tain berry aneurysm clips. Over time, however, as MRA becomes faster, more widely available, and less expensive, its advantages may make it a more attractive alternative in the preoperative workup of patients with AAAs. Aortography Preoperative digital subtraction aortography is not routinely used for diagnosis but rather as an adjunct to other studies in preparation for AAA repair. Being an invasive test, it carries an added risk over other imaging modalities. Aortography is current- ly indicated in the preoperative evaluation of an AAA when (1) the extent of the aneurysm may include the juxtarenal or suprarenal aorta, (2) the clinical history is indicative of lower-extremity arte- rial occlusive disease (i.e., claudication or rest pain), (3) renovas- cular disease may be present, as evidenced by uncontrolled hyper- tension or azotemia, or (4) the patient has previously undergone arterial reconstruction.82 Aortography is superior at evaluating the intraluminal characteristics of the aorta, determining visceral- branch involvement, and delineating variations in the vascular anatomy.11 Aortography has a number of important limitations in compar- ison with CT or MRA. In particular, it is associated with multiple risks that are not incurred with CT or MRA, such as infection, Figure 7 Shown is an MRA of a patient who had undergone arterial thrombosis necessitating emergency thrombectomy and both open infrarenal AAA repair and aortobifemoral bypass off repair, distal embolization, groin hematoma, and local arterial dis- the terminal aorta. The AAA grew between the two previous section.131 There is also a 10% risk of renal failure in patients with repairs and was subsequently managed endovascularly. elevated creatinine levels (≥ 2.5 mg/dl)131; this can often be pre-