Diagnostic algorithm for patients presenting with symptoms suggestive of a ruptured AAA which emphasizes performance of a CT scan with contrast for maximal diagnostic and therapy-planning information
Unfortunately, the incidentally found ruptured AAA on a non-contrast-enhanced CT scan continues to be an all-too-common scenario. Also common is reluctance on the part of the ED physician to rescan the patient with contrast after the diagnosis is made due to a sense of urgency to get the patient on their way to “somewhere else.” Given the rapidity of CT scanning with today’s technology, whether that somewhere else is another hospital capable of treating the condition or the OR in the presenting hospital, there should almost always be time for a complete CT scan if time is utilized efficiently. A recent single center series showed that 88 % of patients ultimately diagnosed with a ruptured abdominal aortic aneurysm survived at least two hours after admission, suggesting that there is time for patients to undergo CT scanning to help assist in clinical decision-making . Similarly, in a 2005 Dutch series of 100 ruptured AAA patients, 21 of whom were treated “palliatively,” the median time from arrival to death in the palliated group was 435 min (range 15 mins–6 days) . In those undergoing treatment, the median time from presentation to operation was 159 min (range 16–1450 mins) with the mortality in the surgical group not being affected by the length of delay (p = 1.0) or obtaining CT imaging (p = 0.34). Since an operating room will rarely be instantly available and interhospital transport, by whatever means, takes time to initiate, there is almost always time to repeat a CT scan with contrast if the surgeon feels it would aid in decision-making.
An alternative strategy for patients with renal insufficiency or other contrast contraindications would be to obtain the non-contrast CT series but leave the patient in the scanner until the imaging is checked for an AAA. If an AAA is present, the scan can be repeated with contrast without having to re-transport the patient in and out of the scanner. This strategy also maintains registration between the pre- and post-contrast scans which can assist in interpretation.
The previous discussion notwithstanding, while contrast-enhanced high-resolution CT imaging is highly desirable, it is not absolutely necessary to successfully perform REVAR. A non-contrast scan coupled with angiographic and/or IVUS evaluations is a common compromise to repeating the CT scan [10, 11]. Furthermore, in the setting of a patient with chronic kidney disease, a CO2 angiogram can be used to replace iodinated contrast, though visualization may somewhat compromised . In a recently reported series of 40 ruptured AAA patients, ten were hemodynamically unstable and were taken to the endovascular suite without any CT imaging whatsoever, being sized and treated based on angiography and IVUS alone .
While compromises may at times be necessary, taking patients for REVAR on the basis of suboptimal imaging will inevitably have a higher failure rate and in the case of a ruptured AAA failure to exclude the aneurysm and staunch the hemorrhage which is not an acceptable outcome. This reinforces the value of an operating endovascular suite, which allows for a relatively seamless transition to open repair if needed. Even more so, it emphasizes the importance of understanding the maneuvers involved in obtaining balloon occlusion of the aorta and subsequently deploying a complete endograft while maintaining balloon occlusion. The exact technique for this will be discussed in another chapter, but it should be recognized that balloon position differs depending on whether the intent is to proceed with REVAR, in which case any balloon deployed needs to be supraceliac, or open repair, in which case the balloon can be a bit lower to allow maintained hepatic and mesenteric perfusion. In either case, the occluding balloon should only be inflated if needed to maintain a reasonable blood pressure and, in the case of open surgery, transitioned to a more distal clamp as soon as possible to minimize the ischemic insult to the visceral organs which can lead to coagulopathy and renal failure [14, 15].
Imaging Is Only Valuable if You Can See It
Under our diagnostic algorithm, since a significant majority of patients will meet the criteria for contrast administration, vascular surgeons can expect high-resolution contrast-enhanced CT scans on most patients they are called about for ruptured AAAs. However, a scan is only as useful as its images are accessible. Fortunately, in today’s interconnected world, most regions will have Internet access to CT scans performed in the outlying emergency rooms or at least within their own system. Alternatively, several HIPPA compliant image-sharing Internet-based services are available under contract. More than ever before, vascular surgeons are able to see their future patient’s vascular anatomy long before they meet them in the flesh, allowing valuable savings in time by permitting direct patient transfer to the facility best suited to their planned repair. In patients being transferred in from an outside hospital, the ability to scrutinize the CT scans prior to patient arrival can permit the patient to bypass the emergency department entirely, proceeding directly to the therapeutic venue of choice, operating room or endovascular suite, as directed by the CT scan images. Thus, in an ideally functioning program, the ruptured AAA patient’s treatment destination will have been determined by a vascular surgeon’s review of a contrast-enhanced CT scan shortly after image acquisition, perhaps while the patient is still in an outside hospital’s emergency department. The determination of the anticipated mode of repair, REVAR or open, sets in motion a coordinated set of notifications and protocol activations specific to the intended mode of repair, the intent being to minimize the number of additional calls needed to move forward with getting ready to receive and treat the patient.
How Low Can It Go?
Long embraced by surgeons, but only sporadically by emergency personnel, the concept of permissive hypotension is another that needs to be taught to your emergency medical services (EMS) personnel. Admittedly a challenging strategy to get comfortable with initially, allowing a patient to remain hypotensive or even inducing a degree of hypotension (hypotensive hemostasis) is a recognized strategy to maintain hemodynamic stability in a ruptured AAA patient by not stressing the tamponade that had to have happened if the patient is still alive. There are limits, however, to how low a patient’s pressure should be allowed to go. Traditionally any pressure in a mentating patient was considered acceptable. A recent analysis of the Immediate Management of Patients with Ruptured aneurysm: Open Versus Endovascular Repair (IMPROVE) trial data, however, suggests that having a blood pressure below 70 mmHg at any time is associated with a 51 % mortality . Others have suggested that blood pressure control is not the only important factor, demonstrating that the total volume of fluids administered before aortic control correlated directly with mortality . A combination approach of fluid limitation to less than 500 ml and systolic blood pressure (SBP) titration to a range of between 50 and100 mmHg, using nitrates as needed to keep it below 100 mmHg, has been reported, although in practice SBP was more often at the upper end of the target range .
In our experience, the easiest means to overcome the psychological obstacle to permissive hypotension is to develop specific order sets for emergency physicians and EMS transport personnel to refer to as they manage the patient. In essence, this gives them permission to hold back on resuscitating a hypotensive patient. We have opted to target a SBP range of 70–100 mmHg to avoid potentially detrimental severe hypotension and maintain a level of comfort with EMS personnel. It should not be overlooked that effective pain management is often all that is needed to generate a reduction in SBP to more acceptable levels, with beta blockade further adding to the desired goal. The most critical and not uncommon scenario to avoid is the patient who is hypertensive from pain and, without pain relief, is a significant risk of conversion to uncontained rupture.
Keeping Your Patient’s Options Open
The primary advantage of being able to view your patient’s imaging prior to transfer is to determine suitability for endovascular or open repair. This, combined with consideration of the availability of requisite personnel, equipment, and surgeon expertise, will determine the venue the patient should be transferred to. Given the value that a venue suitable for operative repair brings in case of REVAR failure, or that imaging brings to the open repair patient who gets aortic balloon occlusion, it is clear that a hybrid suite that offers both imaging and open surgical capabilities is the most desirable. Absent this type of suite, pre-arrival review of the imaging will determine if the patient is going to go to the operating room for open repair or the endovascular suite for REVAR. Although REVAR can be performed with portable fluoroscopy, it is the opinion of these authors that the compromised image quality, acquisition fluidity, and image processing render it an undesirable limitation and one that could preclude offering REVAR to all but the most straightforward of cases.
Even more so than for open repair, the setup of the endovascular room can be complicated, needing to accommodate anesthesia teams and equipment, the radiographic unit, monitors, power injectors, IVUS drivers, and disposables galore. Standardization of the room layout and instrumentation for all EVARs will translate, in the emergency setting, to efficient utilization of time as operator attention can be focused on pre-procedural planning while the room and patient are being prepared per protocol by others in the team. We have developed room layout maps for positioning of all equipment and personnel to simplify preparation of the room and to get it done prior to the patient’s arrival. While many leave the radiographic unit off to the side until the REVAR begins, once the patient is positioned on the table, we generally position the radiographic unit over their mid abdomen, out of the way of anesthesia’s efforts to insert lines and any groin access, yet available to guide placement of central lines or aortic occlusion balloons. Whether the patient is destined for open or endovascular repair, an aortic occlusion balloon can be positioned under fluoroscopic guidance to be inflated if or when needed. If needed, this can usually be accomplished under local anesthesia, while venous access and arterial monitoring lines are being placed by the anesthesia team.
Most standard integrated suites have a floor- or ceiling-mounted angiographic system and a “sliding” radiolucent table to allow for easy patient positioning under fluoroscopy. A control panel is also typically attached tableside under a transparent drape in order to allow the operator to control the table position, radiographic gantry, and fluoroscopic and radiographic settings. A surgeon who is facile with operation of the radiographic equipment can often more expeditiously select desired options and positions than when working through a middleman, the radiology technician, thereby reducing radiation and procedural time. In some setups, the control panel is separated from the tabletop to decrease the clutter around the patient and improve the accessibility that the surgeon has to the patient. While a radiology technician knowledgeable in imaging acquisition and processing software is required in either case, the operator of separated controls cannot be the surgeon or part of the sterile team. Given the emergency nature of REVAR, and the a la carte nature of endovascular procedures in general, it is imperative that there be a person available to fetch supplies. Not only should they be knowledgeable about elective EVAR but also the extra devices and maneuvers that might be required for REVAR. Furthermore, they need to be familiar with inventory and placement of catheters, stents, endografts, and other equipment in the room so that they can be obtained and ready to use on a short notice. Rails are also placed on the side of the moveable radiolucent table to serve as attachment sites for table-mounted retractor systems should the operation be converted to an open procedure.
Observational studies used to assess integrating surgery and radiology in one suite have revealed increased workflow times involving preparation and anesthesia ranging from as little as 18 min to as long as 120 min.  Due to the amount of equipment and personnel involved in such cases, it may be helpful to have a designated team that is familiar with the procedure and the equipment used for aortic aneurysm repairs. Centers with simulation suites may help prepare personnel to reduce workflow times and potentially improve patient outcomes. This will be discussed in a later section.
For elective EVAR, it is not uncommon for an endograft representative to bring devices to the case rather than relying on a hospital’s inventory. In the ruptured scenario, however, there will rarely be sufficient time to rely on a representative so a critical factor in determining whether a hospital can provide REVAR on a routine basis is their willingness to stock a wide variety of sizes of aortic endografts and endograft components, as well as the sheaths, guidewires, catheters, stents, and balloons which may be needed to complete a repair. While not commonly used in elective practice, aorto-uni-iliac (AUI) devices offer some advantages in the ruptured AAA situation, most notably a reasonable degree of hemostasis at the time of initial endograft deployment without having to cannulate the docking junction and deploy the contralateral limb to attain it, though complete hemostasis still requires iliac occluder placement and femoral-femoral bypass grafting. Although an unusual occurrence, AUI endografts have also been employed to cover the contralateral limb of a bifurcate body when the docking junction cannot be successfully cannulated, converting the case to the AUI with femoral-femoral bypass configuration, with iliac occlusion, as needed [20, 21]. Large bore sheaths are typically required (18–24 F) to deliver most aortic stent grafts so these need to be kept in inventory. Critical to the use of aortic occlusion balloons, as described in greater detail in an upcoming chapter, is the availability of two 12Fr × 55–65 cm sheaths to allow endograft deployment over an occlusion balloon with subsequent balloon extraction. In addition, it is important to have a variety of guidewires available with varying tip characteristics to be able to negotiate a variety of vascular anatomies and varying degrees of stiffness to facilitate device tracking through tortuous anatomy.
Given the potential for conversion to open repair, a laparotomy instrument tray and a variety of vascular clamps should be available, which will also come in handy if open femoral access is chosen. Recently, the off-label use of the Perclose ProGlide Suture-Mediated Closure System (Abbott Vascular, Santa Clara, CA) in the “pre-close” configuration of two cross deployed ProGlide devices to permit percutaneous EVAR has gained popularity for its increased speed and reduced wound complications. While something one should begin with electively, in the hands of an experienced operator the deployments of these devices are feasible and can be performed in a rapid fashion, consistent with the urgency of a ruptured AAA . Other devices that may be helpful to have in stock include a variety of peripheral and visceral bare metal or covered stent grafts. The 510 series Palmaz stents can be used as a bailout strategy to treat type Ia endoleaks, while short balloon expandable stents or endografts may be needed to preserve the renal arteries in case of accidental coverage by the main aortic stent graft.