Definitions

RAAA is an abdominal aortic aneurysm (AAA) with extraluminal blood on computed tomography (CT) or noted clinically at the time of surgery. A contained rupture refers to blood outside the aneurysm sac that is confined to the retroperitoneal space, tamponaded by the surrounding tissues. A free rupture refers to bleeding into the peritoneal cavity, without tamponade. A symptomatic, nonruptured AAA is one with back pain or tenderness over the aorta on deep palpation but with an intact aneurysm on CT. The pain is thought to be related to acute expansion of the wall, intramural hemorrhage, wall degeneration, or bleeding into the thrombus and is therefore considered a prelude to actual rupture, which requires urgent repair. Symptomatic aneurysms are not associated with hypotension; however, the prognosis is much better than that of RAAAs (but worse than after elective repair).¹⁴ The inclusion of symptomatic aneurysms in data on RAAAs will artificially improve the data. Those with symptoms and an AAA require rapid diagnosis and management to prevent rupture and its associated adverse outcomes.¹⁵

History

The first successful reconstruction for RAAA was by Henry Bahnson with a homograft in 1953.¹⁶ Before that, the only treatment was aortic ligation. The first reported operation was in 1817 by Astley Cooper, who ligated the aortic bifurcation in a 38-year-old man for a ruptured left external iliac artery aneurysm (29 years before general anesthesia).¹⁷ The patient died on the second postoperative day. Another 11 aortic ligations were attempted before the end of the 19th century; none was successful. Surgeons in the early part of the 20th century fared little better despite using a variety of different materials for ligation (soft rubber catheters, aluminum bands, catgut). Eventually, in 1923, Rudolph Matas successfully ligated the aorta of a 28-year old “field laborer” with a ruptured syphilitic aortic aneurysm.¹⁸ She survived 28 months, succumbing to tuberculosis. Despite this, ligation was not widely embraced, and definitive surgical reconstruction was established after 1953. By 1954, Cooley and DeBakey had treated six patients with a 50% survival rate.¹⁹ Javid and colleagues from Chicago reported another four cases the following year, also with a 50% survival rate, and the Mayo Clinic reported its first two cases in 1956.²⁰ Just as elective open aneurysm reconstruction was rapidly applied to ruptures, so too was endovascular aneurysm repair (EVAR). Following the first description of EVAR in 1991, Hopkinson performed the first EVAR for rupture in Nottingham, England, in 1994.²¹ This, too, has been widely adopted.

Declining Incidence

Reported incidences of RAAA have fluctuated during the last 6 decades. In the 1950s and 1960s, diagnosis was made on clinical grounds (or at autopsy), without CT or other abdominal imaging, which resulted in a low reported incidence. Contemporary data are more reliable. From 1999 to 2009, the Centers for Disease Control and Prevention reported 49,207 deaths from RAAA in the United States,²² with most deaths in the 75- to 84-year age group. This excluded those undergoing successful surgery. Until recently, the incidence of RAAA was thought to be increasing annually. In 2006, a population-based report from Sweden showed that the incidence of RAAA almost doubled between 1971 and 2004.²³ In the United States, between 1951 and 1980, the incidence of AAA rose by sevenfold.²⁴ More specifically, the incidence of RAAA in men increased threefold despite more elective repairs from 1971 to 2004. However, in 2011, a decline in the incidence of ruptured (and intact) AAA began to be reported in most Western populations (Fig. 133-1). In Australian men, the number of deaths from RAAAs fell by 38% between 1999 and 2006²⁵; in New Zealand, the decline during a similar period was 53%.²⁶ In 2012, a review of population-based mortality and hospital admissions in England and Wales from 1979 to 2009 showed a steady increase in deaths from RAAAs, especially in men, until 1996.¹⁰ Then, deaths began to rapidly decline. By 2009, the mortality rate was lower than in 1979. In the United States, this phenomenon has also been observed. In 2012, a retrospective study of 338,278 Medicare beneficiaries from 1995 to 2008 reported that AAA-related deaths halved during the study period, with the greatest decline seen in patients older than 80 years.¹¹

The reason for the declining incidence of RAAA is not clear. It cannot be explained by improved surgical outcomes for RAAA in large centers of excellence. This is because most deaths from RAAA occur before a patient reaches the hospital, so that overall mortality rates from RAAAs remain between 74% and 90%.^1,2,27–29

Population screening has been shown to reduce AAA-related deaths,^30,31 but the decline in mortality due to RAAA began before population screening became widespread. The availability of EVAR may have led to more elective AAA repairs in older patients and those who would previously have been considered unfit for open surgery, which could have reduced the at-risk population for RAAA.³² However, the biggest reduction in absolute numbers of ruptured aneurysms has come from a decline in the prevalence of intact AAA. In 2011, Svensjö et al³³ reported that the prevalence of screen-detected AAAs in the Swedish screening program was “lower than expected” at 1.7%. The U.K. screening program detection rate is now also only 1.7%, much less than the 4% detection rate expected when the program was initiated.³⁴ In the county of Gloucester in England, where population screening has been taking place since 1990, the prevalence has dropped from 4.8% to 1.1% in 65-year-old men.³⁵ This has been attributed to decreased levels of smoking (see Chapter 27).

Mortality of Ruptured Abdominal Aortic Aneurysm

In 1988, an 8-year survey in the southeast of England reported a community mortality rate of 89% for RAAAs.²⁷ Two thirds of patients failed to reach the hospital alive. Another 1988 study from the southwest of England reported a remarkably similar 86% community mortality rate.²⁸ In 2006, a population-based Swedish study²³ with a high autopsy rate reported that the early mortality rate (death in the community or during hospitalization) was 74% and that, as recently as 2004, only 48% of patients underwent repair.

Data from the Danish national registry from 1994 to 2008 show the overall mortality risk from RAAA to be 76%. Again, less than half underwent surgery.³⁶ Postoperative mortality decreased from 51% to 42%. This was attributed to centralization of services and better prehospital care. In 2013, the Swedish vascular database (Swedvasc) also reported an improvement in outcomes for patients with RAAAs.³⁷ Data of 4972 patients with ruptured aneurysms from 1994 to 2010 were reviewed and showed a decline in mortality from 38% to 28%, which was credited to the introduction of EVAR. The most ambitious review of population data was by Mani et al³⁸ using the Vascunet database. In 2011, they collated outcomes for RAAA repair in 7040 patients from national and regional registries in nine countries (Australia, Denmark, Finland, Hungary, Italy, Norway, Sweden, Switzerland, and the United Kingdom). The overall mortality rate was 31.6%, but it declined by 4.2% between 2005 and 2009. This was again attributed to more liberal use of EVAR.

Mortality of Ruptured Abdominal Aortic Aneurysm Repair

A meta-analysis of the first 50 years of RAAA publications noted that the mortality rate for ruptured repair has fallen only 3.5% per decade since the initial successful repairs were reported.⁷ A meta-analysis of publications between 1991 and 2006 suggested no significant overall change in mortality with open surgical repair (OSR) during this period.⁵ This conclusion is supported by data from U.S. Veterans Affairs hospitals and the U.S. National Hospital Discharge Survey database (for the years 1979 to 1997), which have not demonstrated a decline in RAAA mortality.⁷ Between 1994 and 2003, mortality after OSR of RAAA was unchanged on the basis of U.S. Medicare data.³⁹

The high postoperative mortality rates after aortic rupture are secondary to a high incidence of myocardial infarction, renal failure, and multiple organ failure (MOF). Aortic rupture and OSR result in a combination of ischemia-reperfusion injuries, hemorrhagic shock, and lower torso ischemia. The synergistic effect of the total-body ischemia caused by hemorrhagic shock and the lower torso ischemia that occurs during repair, followed by reperfusion secondary to resuscitation and aortic unclamping, has been proposed to explain the high incidence of MOF and mortality after repair. This hypothesis is supported by data from both animal experimentation and human clinical studies.^40,41 The application of endovascular techniques to repair of RAAAs (EVAR) reduces the operative and ischemic insult in two ways. First, it avoids a laparotomy, thus reducing the potential for iatrogenic arterial and venous operative injuries and their associated blood loss. Second, it minimizes the duration and severity of the lower torso ischemic insult. Recent data from large administrative databases in the United States have demonstrated increased application of EVAR to RAAA.^39,42–44 Analysis of mortality rates of EVAR cases between 2000 and 2003 noted a significant reduction in the mortality of RAAA patients treated by EVAR (31.85 vs. 50.8%; P < .001).⁴⁵

Abdominal Aortic Aneurysm Shape and Finite Element Analysis

The engineering technique of finite element analysis has been applied to AAAs to estimate regional variations in peak wall stress throughout the entire aneurysm wall. With use of CT scan data, a mesh is applied to the aortic wall, and finite element analysis is used to calculate peak wall stress for many small segments of the aortic wall to provide a visual representation of peak wall stress (Fig. 133-2). Early three-dimensional representations of peak wall stress noted that the posterior wall of the aorta had higher values corresponding to the site where most AAAs were noted in clinical observations and autopsy studies to have ruptured.^48,49

Initial studies assumed that AAAs had uniform wall thickness and material isotropy (uniform strength in all orientations), but several studies^50–52 show this is not the case. There are localized “hot spots” of matrix metalloproteinase (MMP) activity that could cause focal weakening of the aneurysm and rupture at relatively low levels of intraluminal pressure. Newer models include growth and remodeling theory that allows evolving wall thickness, stiffness, regional heterogeneity, and fluid-structure interactions within the aneurysm sac to be analyzed.^53,54 As a result, we may not be far off from the day when individual risk of rupture can be accurately estimated from conventional CT scans.

Role of Aortic Thrombus

In 1965, Martin⁵⁵ surmised that as an aneurysm develops, it becomes lined with thrombus, which weakens it by interfering with nutrition of that segment of the wall. Contemporary studies confirm this, showing that intraluminal thrombus is not protective and weakens the aneurysm wall.⁵⁶ In 2000, using a pressure transducer during open aneurysm repair, Schurink et al⁵⁷ confirmed that intraluminal thrombus does not reduce pressure near the aneurysm wall. Vorp et al⁵⁸ also confirmed localized hypoxia in regions of thicker thrombus that might lead to localized wall neovascularization, inflammation, and regional wall thinning. Hypoxia also affects the function of vascular smooth muscle cells, causing them to secrete more collagenase than in normoxic conditions, with less elastin and collagen production.

Aneurysm thrombus is also not inert. MMPs are a family of 28 endopeptidases that comprise collagenases, gelatinases, and stromelysins. They degrade extracellular tissues, cleave cell surface receptors, and are involved in tissue remodeling. They are inhibited by four endogenous tissue proteins called tissue inhibitors of metalloproteinases. Intraluminal thrombus contains high levels of MMP-2 and MMP-9, trapped neutrophils rich in MMP-9, and neutrophil gelatinase-associated lipocalin, which neutralizes the defensive actions of tissue inhibitors of metalloproteinases. An autopsy study of 78 patients who died of infrarenal RAAAs showed that 80% of ruptures occurred at the site of mural thrombus.⁵⁹ This was supported by CT studies of patients admitted with rupture, which showed that most ruptures occurred through the thrombus or at its edge. Others argue that cracks or fissures in the intraluminal thrombus due to proteolytic enzymes on the luminal surface of the clot are what really cause rupture.⁶⁰ However, consensus seems to be building. A Dutch report⁶¹ in 2013, while accepting a role for fissure formation, confirmed that intraluminal thrombus thickness was associated with vascular smooth muscle cell apoptosis (or cell death), elastin degradation, and high levels of MMP-2 and correlated with aneurysm rupture. (Details of aneurysm wall biology are discussed in Chapter 9).

Signs and Symptoms

The classic presentation of RAAA is a male patient older than 60 years complaining of acute-onset abdominal and back pain. Back pain is caused by rupture of the aneurysm into the retroperitoneal space and is severe and unremitting. Patients may describe pain radiating to the testes, inguinal canal, or rectum. Some patients may describe hip pain due to psoas irritation. On examination, the patient is usually pale, diaphoretic, and hypotensive with a tender, expansile abdominal mass. Rarely, there may be flank ecchymosis due to tracking of retroperitoneal blood. There may be documentation of a prior diagnosis of AAA.

Differential Diagnosis

In patients older than 50 years with hypotension or syncope (or both), consideration of RAAA is critical because it has the worst prognosis of conditions included in the differential diagnosis. A rapid, accurate history and examination are critical. The differential diagnosis may include renal colic, diverticulitis, pancreatitis, gastrointestinal hemorrhage, inferior myocardial infarction, and perforated ulcer. Although the signs and symptoms of RAAA can be clear-cut, it may be difficult to recognize in the early stages. Many patients will initially have relatively normal blood pressure on arrival in the emergency department, after fluid resuscitation en route. Some may give a history of pain extending during the course of 3 or 4 days as the AAA has bled, sealed, and then bled again. In the affected age group, chronic back problems are common, so the physician may be tempted to ascribe symptoms to an exacerbation of a long-standing problem. The other misdiagnosis is to confuse the presentation with ureteral colic. Symptoms may be incorrectly attributed to acute diverticulitis (especially if leukocytosis is present) or a perforated duodenal ulcer. Rare presentations include rupture into an adjacent structure, such as an acute gastrointestinal bleed due to a primary aortoduodenal fistula or an aortocaval fistula that presents as an expansile abdominal mass, loud machinery-like bruit, or thrill with new-onset acute congestive heart failure from a high-output fistula.

Studies have examined the clinical findings in patients in whom RAAA was subsequently diagnosed.⁶² In only 23% was a definitive and immediate diagnosis of RAAA made by the first physician who examined the patient.⁶³ The rate of incorrect diagnosis ranges from 16% to 60%.⁶⁴ The most common misdiagnoses were renal colic, perforated viscus, diverticulitis, gastrointestinal hemorrhage, and ischemic bowel. The initial manifestation of renal colic occurs infrequently in patients older than 50 years. The classic triad of pain, hypotension, and pulsatile mass was present in only 9% of the misdiagnosed group compared with 34% of the correctly diagnosed group. The presence of a pulsatile mass was identified in 72% of those correctly diagnosed but in only 26% of the misdiagnosed patients. Thus, the lack of a pulsatile mass frequently confuses the diagnosis. Furthermore, the use of ultrasound in older studies was reported as being consistent with rupture in only 51% of cases.⁶⁴

Diagnostic Evaluation

Patient Triage and Transfer to Appropriate Institutions

RAAA is a vascular surgical emergency, and when the diagnosis is being considered, immediate vascular surgery consultation is critical. Hospitals that lack vascular surgery expertise and cannot offer definitive treatments should consider establishing networks with larger institutions that have vascular surgery services and can offer repair by endovascular or open surgical means, as needed. The impact of transferring RAAA patients to regional centers where repair can be carried out by experienced vascular teams has been studied. Rural hospitals without vascular surgery expertise tend to face a higher burden of RAAA patients, and national trends suggest that they are more likely to transfer patients to regional centers.⁷⁸ Although patient transfer might increase the time of arrival from the initial hospital to the operating room, most studies suggest that high-volume regional centers significantly lower the mortality for RAAA patients.⁷⁹ Furthermore, as U.S. nationwide trends suggest increased use of EVAR for RAAA, it is likely that regionalization of patient care will have a significant impact on management of RAAA patients.⁸⁰

Permissive Hypotension

Preoperative resuscitation of RAAA patients with hypotension must be judicious.^81–84 Large volumes of intravenous fluids and a rise in blood pressure can lead to further hemorrhage by overcoming the tamponade that stabilized the initial rupture. It also causes hemodilution, coagulopathy, hypothermia, and acidosis, and further deterioration.⁸⁵ Similar to transfusion protocols that restrict aggressive fluid resuscitation in hypotensive trauma patients with hemorrhagic shock, permissive hypotension for RAAA patients is recommended. Fluid resuscitation is minimized to maintain consciousness, to prevent ST depression, and usually to maintain a systolic pressures of 70 to 80 mm Hg.⁸⁶ Crawford initially suggested minimal fluid resuscitation to maintain systolic blood pressure at 50 to 70 mm Hg in patients with RAAA.⁸² Although, all contemporary algorithms for management of RAAA patients include permissive hypotensive resuscitation,⁸⁷ a balance must be sought between organ ischemia from inadequate resuscitation and the risk of rebleeding from overaggressive resuscitation. Aggressive volume resuscitation during initial management of RAAA before proximal aortic control is a predictor of increased postoperative mortality.⁸⁸ Therefore, resuscitation that maintains the patient in a conscious state and prevents ST-segment depression is used to stabilize patients until definitive repair can be carried out.⁸⁴ Currently, evidence regarding resuscitation with blood versus crystalloids is limited. If blood is available, it should accompany the patient during transfer and can be given instead of crystalloid solutions to maintain consciousness.

Operative Preparation

In the initial evaluation blood should be crossmatched so that it will be available at surgery. In the operating room, trained anesthesia, nursing, and technical personnel can prepare the patient for surgical operative or endovascular intervention. Large-bore access, insertion of an arterial line, and placement of a Foley catheter can be done simultaneously. The patient is prepared and draped awake before anesthesia and is induced with agents designed to have minimal effect on blood pressure. This allows the repair to be commenced immediately after induction. Alternatively, EVAR for RAAA can be carried out through a percutaneous approach, with local anesthesia and conscious sedation.

Initial Management

Technique