Abdominal Aortic Emergencies Paul N. Rogers

Paul N. Rogers

Abdominal/back pain and hypotension = a ruptured AAA, unless proven otherwise.

Urological and orthopedic wards are a cemetery for ruptured AAA cases.

Presentation

The diagnosis of a leaking abdominal aortic aneurysm (AAA) is usually not difficult to make. Typically the patient presents with a sudden onset of acute lumbar backache, abdominal pain and collapse associated with hypotension. On examina- tion the presence of a pulsatile abdominal mass confirms the diagnosis. In this situation the patient proceeds directly to the operating room with a delay only to allow cross-matched blood to become available if the patient is stable.

Atypical Presentation

Not infrequently however, the diagnosis can be difficult to make. There may be no history of collapse and the patient may be normotensive on admission. The only clue may be non-specific back or abdominal pain. A pulsatile mass may not be palpable. Ruptured AAA patients are frequently obese; thinner patients tend to notice their AAA and present early for an elective repair. A leaking AAA may be mislabeled as “ureteric colic” but the absence of microscopic hematuria should alert one to the possibility that a leaking aneurysm is responsible for the symptoms.

A high index of suspicion is important to prevent the diagnosis of a leaking

AAA being overlooked. In appropriate individuals, particularly men in late-middle

and old age, if significant and unexplained abdominal or back pain causes the

patient to present acutely, abdominal aneurysms should be excluded by means of

ultrasound or CT.

The Diagnostic Dilemma

A different diagnostic dilemma occurs in the patient who is known to have an aneurysm and who presents with abdominal or back pain, which may or may not be related to the aneurysm. The difficulty here is that a small, contained, “herald”

leak from an aneurysm might produce pain without any hemodynamic instability.

Examination in these patients may be unhelpful in that the aneurysm may not be tender. These patients are at high risk of a further bleed from the aneurysm and this could be sudden and catastrophic. For this reason it is important that they are iden- tified appropriately and have an operation before a major,possibly fatal,hemorrhage occurs.The difficulty of course is that such a patient might easily have another cause for the symptoms, mechanical backache for example, which is unrelated to the an- eurysm. Here, an operation is clearly not in the patient’s best interests, particularly if his or her general health is poor. This dilemma, of operating without delay in pa- tients who require it yet avoiding operation in those in whom it is not necessary, is a difficult one, sometimes even for experienced clinicians to resolve.An emergency CT scan is indicated in this situation to delineate the AAA and presence of any associated leak – usually into the retroperitoneum. In general however, in this situa- tion it is safer to err on the side of operating on too many rather than too few patients.

Who Should Have an Operation?

A useful rule of thumb is that the chances of survival in a patient with a rup-

tured AAA are directly proportional to the blood pressure on admission. Shocked

patients rarely survive; sure,they may survive the operation but usually do not leave

hospital through the front door. Consequently, it has been proposed that operating

on shocked ruptured AAA patients is a futile waste of resources.Another view is that

you should proceed with the operation unless the patient is clearly “agonal” or

known to suffer from an incurable disease. You may be able to save the occasional

patient and gain additional experience, which may help you to save the next rupture

patient. These issues of philosophy of care are for the individual surgeon to resolve

with his patients. A scoring system has been devised that aims to help with this

decision-making. The so-called Hardman criteria relate the presence of several

easily determined variables to the likelihood of survival from surgery from a rup-

tured aneurysm.

The Hardman

Criteria

Age >76

History of unconsciousness Hemoglobin <9.0 g/dl Creatinine >190 µmol/l ECG evidence of ischemia

If three or more criteria are present the mortality is 100%

If two are present mortality is 72%

If one, 37%

It is impossible to fill a bucket which has a hole.

The Operation

Once the diagnosis of aortic rupture has been established, or strongly sus- pected, the patient should be rushed to the operating theatre without delay. Do not even bother with additional lines and intravenous fluids as what you pour in will pour out, and increasing the blood pressure will increase the bleeding. Aim for stable hypotension in resuscitation.

Preparation  “Prep and drape” for surgery while the anesthetic team estab- lishes the appropriate monitoring lines. Do not allow them, however, to waste time by inserting unnecessary gimmicks such as the pulmonary arterial catheter.

Anesthesia should not be induced until you are ready to make the skin incision; not infrequently the administration of muscle relaxants at induction, and the subse- quent relaxation of the abdominal wall, is sufficient to permit a further bleed from the aneurysm with an immediate hemodynamic collapse. Remember: your clamp on the aorta proximal to the aneurysm is more important that anything else.

Incision  Open the abdomen through a long mid-line incision extending from the xiphisternum to a point mid way between the umbilicus and the symphysis pubis.Occasionally,if the distal iliac arteries are to be approached,the incision must be extended. In most cases however, for the insertion of a simple aortic tube graft, an incision as described is adequate.

1

Hardman DT, Fisher CM, Patel MI, Neale M, Chambers J, Lane R, Appleberg M (1996)

Ruptured abdominal aortic aneurysms: who should be offered surgery? J Vasc Surg

23:123–129.

Proximal Control  Upon entering the peritoneal cavity, the diagnosis is immediately confirmed by the presence of a large retroperitoneal hematoma. The first priority is to obtain control of the aorta proximal to the aneurysm. In the majority of patients who are stable at this stage (with a contained retroperitoneal leak), there is time to approach the aorta above the aneurysm just below the level of the renal arteries. In patients who are unstable, rapid control of aortic bleeding may be obtained by approaching the aorta just under the diaphragm and temporarily applying a clamp there until the infra-renal aorta can be dissected.

Subdiaphragmatic Aortic Control  Remember how you do truncal vago- tomy? Of course you don’t! So pay attention. Incise the phrenoesophageal ligament overlying the esophagus (feel the nasogastric tube underneath). With your index finger bluntly mobilize the esophagus to the right; forget about hemostasis at this stage. Now feel the aorta pulsating to the left of the esophagus, dissect with your index on both sides of the aorta until you feel the spine.Apply a straight aortic clamp, pushing it “onto” the spine. Leave a few packs to provide hemostasis and proceed as below.

Infra-renal Aortic Control  Returning to the matter of isolation of the aortic neck note that the main principle to be observed is to avoid disturbing the retro- peritoneal hematoma while gaining control of the proximal aorta. Once you enter the retroperitoneum at the neck’s level, dissect bluntly using your finger or the tip of the suction apparatus, to identify and isolate the neck of the aneurysm. Once the neck is identified carry on down both sides of the aorta until the vertebral bodies are reached. Do not attempt to encircle the aorta with a tape.Apply a straight aortic clamp in an antero–posterior direction with the tips of the jaws of the clamp rest- ing against the vertebral bodies. Placement of this clamp is facilitated by placing the index and middle fingers of your non-dominant hand on either side of the aorta so that the vertebral bodies can be palpated. The jaws of the open clamp are then slid along the backs of the fingers until the clamp lies in the appropriate position. Now you can remove the subdiaphragmatic clamp.

Juxtarenal Neck  Occasionally the aneurysm extends close to the origin of

the renal arteries. If this is the case then the neck of the aneurysm will be obscured

by the left renal vein, which may be stretched anteriorly. Care must be taken that the

vein is not damaged.It may be divided to facilitate access to the aneurysm neck.This

is done by very gently mobilizing the vein from the underlying aorta. It should be

ligated securely as close to the vena cava as prudence permits. If this is done then

the vein may be ligated with impunity and the kidney will not be endangered,

because collateral venous drainage will take place via the adrenal and gonadal anas-

tomoses. How do you know that effective proximal control has been achieved?

Simple – the retroperitoneal hematoma stops pulsating. If it pulsates your clamp is not properly placed. Re-apply it!

Distal Control  The next part of the dissection to identify the common iliac arteries is often more difficult. Under normal circumstances the pelvis is the site of accumulation of much of the retroperitoneal hematoma and the iliac arteries are buried within this. The arteries are difficult to locate not only because they are buried in hematoma but because with the aorta clamped proximally,there is no pul- sation to guide the operator. In most patients, however, the presence of atheroma in the vessels makes palpation in the depths of the hematoma possible. Again, the use of the suction apparatus facilitates isolation of the iliac vessels. Otherwise, dig with your fingers within the hematoma and “fish” the iliacs out. As with the aorta, no attempt should be made to encircle the iliac vessels with tapes. This invariably produces damage to the iliac veins, which is a disaster. It is sufficient to clear the an- terior and lateral aspects of the iliac vessels and apply clamps in an anteroposterior manner as before.

An Alternative – Balloon Control  After proximal control has been achieved and when the iliacs are immersed within a huge hematoma you may also rapidly open the aneurysm sac and shove a Foley or large Fogarty catheter into each iliac artery, inflating the balloons to produce temporary distal control.

Aortic Replacement  Once the proximal and distal arterial tree is controlled, incise the aneurysm sac in a longitudinal fashion.Evacuate the clot and control back bleeding from any patent lumbar arteries and the inferior mesenteric artery with sutures within the aneurysm sac. A small self-retaining retractor placed within the aneurysm sac to retract its cut edges facilitates this and the next few stages of the procedure. The proportion of patients in whom aortic replacement with a simple tube graft can be achieved varies widely from surgeon to surgeon and center to center. We believe that in the majority of patients insertion of a tube graft can be achieved quite satisfactorily.The advantages of this are that limitation of dissection in the pelvis minimizes the risk of damage to the iliac veins and also damage to the autonomic nerves in the pelvis. Furthermore, there seems little point in extending the length of what is already a challenging operation by inserting a bifurcation graft unnecessarily. Obviously there are circumstances when a tube graft is not accept- able – namely when the patient has occlusive aorto-iliac disease, when the iliac arteries are also significantly aneurysmal, or in some situations when the bifurca- tion is widely splayed so that the orifices of the common iliac arteries are widely separated.

Take care when fashioning the aorta to receive the graft. The longitudinal

incision in the aortic sac should be terminated at both ends by a transverse incision

so that the incision becomes T-shaped at each end. The limbs of the ‘T’ at either end should not extend more than 50% of the circumference of the normal aorta.

Suture the graft in place using monofilament material so that a parachute technique can be used. This allows you to visualize clearly the placement of the in- dividual posterior sutures. Large bites of the posterior aortic wall should be taken because the tissues in this situation are often very poor. Furthermore, leaks that occur after completion of the anastomosis are notoriously difficult to repair if they are situated at the back wall. Once the upper anastomosis has been completed, a clamp is applied to the graft just below the anastomosis and the clamp on the aorta then released. Assuming there are no significant leaks at the upper end, attention is turned to the distal anastomosis. This is completed in a similar fashion to the pro- ximal anastomosis. Back-bleeding from the iliac vessels should be checked before the distal anastomosis is completed.Likewise,the graft should be flushed with saline and one or two “strokes”of the patient’s own cardiac output to clear it of thrombotic junk. If there is no back-bleeding it may be necessary to pass balloon embolectomy catheters into the iliac systems to check that there has been no intra-vascular throm- bus formation. Once the distal anastomosis has been completed and found to be secure, the iliac clamps should be released individually allowing time for any hypo- tension to recover before the second clamp is removed. The anesthesia team will appreciate a warning from you that the time is approaching for removal of the clamps, allowing them to be well ahead with fluid replacement. Inadequate fluid replacement at this stage will result in significant hypotension when the iliac clamps are released.

A Word About Heparin  It is clearly not sensible to administer systemic heparin prior to cross-clamping in patients who are bleeding to death from an aortic rupture. In patients in whom surgery has been carried out for suspected rupture, however, and in whom no rupture is found at operation, then systemic heparin- ization according to the surgeon’s normal practice should be carried out. It is per- missible, however, to heparinize locally the iliac vessels once the aneurysm sac has been opened and back-bleeding from the small vessels has been controlled.

Heparinized saline may be flushed down each of the iliac vessels in turn before re- applying the iliac cross-clamps. No consensus on the need for this practice has been reached and in the vast majority of patients it appears to be unnecessary.

Abdominal closure  The large retroperitoneal hematoma and visceral

swelling resulting from shock, resuscitation, re-perfusion and exposure, common-

ly produce severe intra-abdominal hypertension, which becomes manifest after

closure of the abdomen. Rather than closing under excessive tension use temporary

abdominal closure as discussed in

Chap. 36, and come back to close the abdomen

another day.Avoidance of abdominal compartment syndrome is crucial for survival

in these physiologically compromised patients in whom any further derangement may be the straw that breaks the camel’s back.

In emergency operations for AAA simplicity of the operation is a key for survival: rapid and atraumatic control, avoidance of injury to large veins, tube graft, minimal blood loss, and rapid surgery.

Many patients who reach the operating table will survive the operation only to die in its aftermath,usually due to associated medical illnesses such as myocardial infarction.A successful outcome therefore requires excellent postoperative ICU care as well as competent surgery. The operation is only half the battle.

In ruptured AAA the operation is commonly the beginning of the end-the end arriving postoperatively (

Fig. 37.1).

Aortic Occlusion

This emergency is characterized by acute ischaemia of the legs with mottling of the skin of the lower trunk. It occurs for three reasons:

 Saddle embolus. A large clot originating from the heart occludes the aortic bifurcation. The patient most likely will have signs of atrial fibrillation or a recent history of acute myocardial infarction.

 Aortic thrombosis. The patient probably has a history of pre-existing arterial disease suggestive of aorto-iliac involvement. Occasionally this disaster will occur

Fig. 37.1. AAA: common outcome…

unannounced in a patient who is desperately ill for some other reason. Extreme dehydration, for example, may cause “sludging” of major vessels if there has been some pre-existing atheroma. Malignancy may produce intra-arterial thrombosis.

 Aortic dissection. Suspect this if there is a history of interscapular pain or chest pain associated with obvious hypertension.Look for evidence of other pulse deficits or signs of visceral ischemia suggesting involvement of other aortic branches.

Management

This depends on the etiology and the presence of any relevant underlying pathology.Embolism may often be dealt with easily by bilateral transfemoral embol- ectomy under local anesthetic. Thrombosis on pre-existing atheroma is a more difficult problem. Catheter thrombectomy is unlikely to be successful either in the short or long term. If the patient is very fit (unlikely) aorto-femoral bypass may be indicated. More likely an extra-anatomic bypass (axillo-femoral) may be feasible, always assuming that any underlying illness is not likely to cause the patient’s demise in the immediate future. Often these patients are not fit for any intervention and the aortic thrombosis is an indication that the end is near.

Aortic dissection is a complex illness and its management is variable. The

mainstay is control of hypertension and relief of major vessel occlusion by endo-

vascular “fenestration” of the dissection. The details of this therapy are beyond the

scope of this little book.