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VASCULAR SYSTEM MESENTERIC REVASCULARIZATION PROCEDURES — 1

DOI 10.2310/7800.2109

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MESENTERIC REVASCULARIZA-TION PROCEDURES

Ravi Dhanisetty, MD, Scott Musicant, MD, Lloyd M. Taylor, Jr, MD, FACS, and Gregory L. Moneta, MD

artery stenosis associated with chronic mesenteric ischemia.3,4

Although it is a technically difficult examination to perform,

in experienced hands, the sensitivity of duplex scanning for

detecting lesions in the superior mesenteric artery (SMA) and

celiac artery is 92% and 87%, respectively. When compared

with catheter-based angiography, the overall accuracy for

detection of a 70% lesion in the SMA and celiac artery

was 96% and 82%, respectively.5 By itself, however, duplex

scanning is not sufficient for planning a mesenteric revascu-

larization procedure.

Multidetector CT angiography is the most frequently used

technique for the diagnosis of mesenteric artery stenosis or

occlusions consistent with mesenteric ischemia. Multidetec-

tor CT angiography has in many cases replaced other modal-

ities as the imaging study of choice for evaluation of chronic

mesenteric ischemia [see Figure 2]. It can accurately identifysignificant stenosis in the celiac artery and SMA, identify

significant visceral collaterals, and exclude other potential

intra-abdominal processes.6,7 CT angiography has higher spa-

tial resolution and allows for assessment of visceral branches,

including the inferior mesenteric artery, with greater accuracy

than contrast-enhanced magnetic resonance angiography.8,9

Mesenteric ischemia is encountered infrequently. To date,

there have been no randomized, controlled trials comparing

treatment modalities for either acute or chronic mesenteric

ischemia. Consequently, decisions on how to treat this con-

dition must be based on a few large case series in which a

variety of procedures were used.

Overall evaluation and management of acute mesenteric

ischemia are addressed more fully elsewhere. In what follows,

we focus specifically on the operative techniques used to treat

mesenteric ischemia (whether chronic or acute) and discuss

the available literature supporting their use. The appropriate

technique for a particular patient varies according to the

individual anatomy and intraoperative findings. The relevant

surgical procedures may be conveniently divided into those

employed for chronic mesenteric ischemia and those employed

for acute ischemia.

Procedures for Chronic Intestinal Ischemia

In 1936, J. E. Dunphy was the first to suggest that timely

diagnosis and intervention for mesenteric artery occlusive

disease may prevent intestinal infarction.1 It is now clear that

optimal treatment of mesenteric ischemia depends on prompt

diagnosis and that a high index of suspicion is vital.

Patients with chronic intestinal ischemia generally, but not

always, report experiencing colicky, dull, or aching abdomi-

nal pain, primarily located in the epigastrium but occasionally

radiating to the back. Symptoms typically begin 15 to 30

minutes after eating and may last as long as 3 to 4 hours.

Peritonitis is not a characteristic of reversible intestinal isch-

emia; rather, it is indicative of intestinal infarction. Chronic

postprandial abdominal symptoms result in markedly reduced

food intake (so-called food fear),2 which generally leads to

weight loss.

Physical examination often yields no significant abdominal

findings. Abdominal bruits may be audible but are a non-

specific finding. Patients often, but not always, show evidence

of atherosclerotic disease in other vascular territories. Bowel

habits vary, ranging from normal elimination to diarrhea or

constipation.

Mesenteric ischemia is a clinical diagnosis. Imaging studies

are therefore used to confirm mesenteric artery stenosis orocclusion, supportive of a diagnosis of mesenteric ischemia.

Useful imaging modalities include duplex ultrasonography,

contrast angiography, multi-detector computed tomographic

(CT) angiography, and magnetic resonance angiography.

Duplex scanning is effective in detecting visceral artery steno-

sis [see Figure 1] and may allow earlier detection of visceral

Figure 1 Example of a duplex spectral waveform with

comparative arteriography in a patient with superior

mesenteric artery (SMA) stenosis. The peak systolic

velocity (> 550 cm/s) is dramatically increased over normal

(< 275 cm/s).

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MESENTERIC REVASCULARIZATION PROCEDURES — 2

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dangerous. Appropriate magnification views generally allow

characterization of the proximal SMA beyond its origin, even

without selective catheterization of the SMA. Intra-arterial

digital subtraction techniques are usually adequate for lateral

views and require less contrast material than other techniques.

Arteriography also demonstrates coexisting lesions of the

aorta and of the renal and iliac arteries that may be important

in planning revascularization.

Essentially all patients with peripheral artery disease have

some degree of concomitant coronary artery disease (CAD).

Although no symptoms of CAD may be evident, care must

still be taken to provide perioperative cardiac protection.

Perioperative beta blockade, antiplatelet therapy, and statin

medications should be routinely employed whenever possible

in patients undergoing elective arterial reconstructive

procedures.

If the patient is undergoing a bypass procedure, the choice

of graft material should be addressed. In general, prosthetic

grafts work well for mesenteric artery bypasses. However, the

entire abdomen and both legs should still be included in the

operative field in case autologous vein proves necessaryfor the bypass conduit. Autologous vein is often required in

cases involving bowel resection and may also be preferable

for bypasses to smaller visceral vessels. If an autologous vein

bypass procedure is planned, preoperative duplex scanning of

the greater saphenous and femoral veins is recommended to

facilitate selection of the best available vein for the conduit.

Together with noncontrast images, CT, in many cases, offers

enough anatomic details to plan open procedures. Limita-

tions include contrast-related nephropathy, hypersensitivity

reactions, and inaccurate timing of contrast infusion that may

lead to an indeterminate study and delayed diagnosis.

Arteriography is the traditional imaging technique employed

in planning mesenteric revascularization for chronic intestinal

ischemia [see Figure 3 and Figure 4]. Lateral and anteroposte-

rior views of the aorta are required for full evaluation of the

severity of visceral stenosis or occlusion and the extent of col-

lateral development. In most cases, a transfemoral Seldinger

technique is suitable, although in the setting of iliofemoral

occlusive disease, a transaxillary approach is occasionallyrequired. Between 60 and 100 mL of contrast material is

required for appropriate lateral and anteroposterior views of

the abdominal aorta. Visceral artery lesions are usually ostial

but may extend beyond the orifice of the vessel as a posterior

plaque, especially in the SMA. Selective catheterization of

the main intestinal arteries is rarely necessary and may be

Figure 2 Computed tomographic angiography is being used

more frequently to demonstrate mesenteric artery lesions.

With three-dimensional reconstruction, segmental stenosis

or occlusions can be demonstrated in mesenteric arteries.

Above is an example of proximal occlusion (arrow) of the

superior mesenteric artery with distal reconstitution via

collaterals.

Figure 3 A lateral aortogram clearly shows severe stenosis

of the superior mesenteric artery (arrow) in a patient with

intestinal ischemia.


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Visceral Endarterectomy

Visceral endarterectomy for treatment of mesenteric isch-

emia was first described in 1958 by Shaw and Maynard,10

who performed endarterectomy of the SMA in a blind,

retrograde fashion through a distal arteriotomy. At present,

retrograde endarterectomy cannot be recommended.

The SMA can be approached directly once control of the

supraceliac aorta has been obtained.11 A longitudinal incision

is made across the origin of the SMA, and an endarterectomy

is performed. In most patients, the exposure is limited.

This direct approach may be considered when the SMA is

widely separated from the renal arteries and the visceral

aorta is relatively free of disease; however, this scenario is

uncommon.A more versatile endarterectomy technique is transaortic

endarterectomy.12 This procedure involves a posterolateral

approach to the aorta, in which the aorta is exposed trans-

peritoneally with medial visceral rotation. Alternatively, a

completely retroperitoneal approach may be taken. The main

disadvantage of the retroperitoneal approach is that it restricts

the surgeon’s ability to assess the bowel at the completion of

revascularization.

Transaortic endarterectomy Step 1: incision and initial

approach A midline incision is recommended. A complete

medial visceral rotation is performed, with the left kidney left

in its bed.

Step 2: exposure The lateral aorta is exposed, and theceliac artery and the SMA may be identified anteriorly; the

left renal artery lies posteriorly.

Step 3: endarterectomy A trapdoor incision is made in the

aortic wall in such a way as to encompass the orifices of the

SMA and the celiac artery. Partial occlusion of the aorta with

a clamp is sometimes possible, but in most cases, complete

aortic occlusion is required. If necessary, the aortotomy can

be extended distally and posteriorly to include the renal artery

orifices as well.

Among the advantages of this operation are that it permits

simultaneous endarterectomy of the aorta and all visceral

vessel orifices and that it does not require the use of

prosthetic material [see Figure 4]. The disadvantages include

the potential risks associated with suprarenal clamping (e.g.,

cardiac overload, renal and lower extremity embolization,

and ischemia). Because of these risks, the need for more

extensive dissection, and the unfamiliarity of most surgeons

with this procedure, arterial bypass procedures are generally

preferred for treatment of chronic mesenteric ischemia.

Mesenteric Arterial Bypass

Technical considerations Single-vessel versus multiple-

vessel revascularization There are two schools of thought

on the extent of revascularization for chronic mesenteric

ischemia. Proponents of so-called complete revascularization

advocate revascularization of both the celiac artery and the

SMA and suggest that this approach makes recurrent isch-

emia less likely should one graft or graft limb undergo throm-

bosis.13 In a 1992 study, overall graft patency and survival

were better in patients who underwent multiple-vessel bypassthan in those who underwent single-vessel bypass. The inves-

tigators concluded that multiple-vessel bypass patients were

likely to remain asymptomatic because of the presence of

additional grafts or graft limbs that remained patent.13

Others maintain that the critical vessel involved in chronic

mesenteric ischemia is the SMA and argue that bypass to

the SMA alone is a relatively simple procedure that relieves

symptoms of mesenteric ischemia. In a 2000 study evaluating

49 patients who underwent bypass to the SMA alone, the

9-year primary assisted graft patency rate was 79% and the

5-year survival rate was 61%14 —results equivalent to those

noted in contemporary studies of multiple-vessel revascular-

ization for chronic intestinal ischemia.15

Antegrade versus retrograde bypass Mesenteric bypass grafts

may originate either above or below the renal arteries. Bypassgrafts are considered antegrade if they originate on the ante-

rior surface of the abdominal aorta cephalad to the celiac

artery and retrograde if they originate from the infrarenal

aorta or a common iliac artery. The distal thoracic aorta can

also serve as an inflow site for antegrade mesenteric bypass.

Antegrade bypass from the supraceliac aorta, using either

Figure 4 Lateral aortogram showing so-called coral reef

atheroma involving the visceral aorta with occlusion of the

origin of the superior mesenteric artery. A patient with

mesenteric ischemia and this angiogram may be best treated

with transaortic endarterectomy.


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prosthetic material or autologous vein, has certain advan-

tages, including a straight graft configuration that minimizes

turbulence and graft kinking. Typically, there is also reduced

atherosclerotic calcification in the supraceliac aorta.16 The

disadvantages of antegrade bypass are similar to those of

visceral endarterectomy and derive from the need to clamp

the supraceliac aorta for the proximal anastomosis. As with

visceral endarterectomy, partial occlusion clamping is theo-

retically possible but not always practical. Clamping of the

supraceliac aorta may increase the risk of cardiac events,

visceral or renal emboli, and ischemia. One prerequisite for

use of the supraceliac aorta in an antegrade bypass is that the

vessel must be angiographically normal to ensure that it can

safely be clamped. It should also be kept in mind that reop-

eration on the supraceliac aorta is difficult: once this site has

been used, reexposure generally is not safe.

Antegrade bypass Step 1: incision and initial approach

Supraceliac aorta–visceral artery bypass is performed through

an upper midline incision. Self-retaining retractors are very

helpful.

Step 2: exposure The dissection begins with division of the

gastrohepatic ligament and retraction of the left lobe of the

liver to the right, followed by incision of the diaphragmaticcrus and exposure of the anterior aspect of the aorta.

Step 3: choice of graft In clean cases with no intestinal

necrosis or perforation, we use woven Dacron grafts. If a

single-vessel bypass is to be performed, a single limb is cut

from the bifurcated graft, incorporating a flange of the main

body of the bifurcated graft for the proximal anastomosis.

Autologous vein grafts are usually reserved for contaminated

cases. The femoral vein is an excellent autogenous conduit

for mesenteric arterial bypass.

Step 4: anastomosis of graft to supraceliac aorta and visceral

artery If the celiac artery alone is to be revascularized, the

usual procedure is to perform an end-to-side proximal

anastomosis to the aorta, followed by an end-to-side distal

anastomosis to the common hepatic artery. If the SMA alone

is to be revascularized, it is generally necessary to tunnel thegraft beneath the pancreas to the inferior border of the pan-

creas and then perform an end-to-side anastomosis to the

SMA at that level [see Figure 5a]. Extreme care must be

exercised in developing the retropancreatic tunnel. If this area

appears too narrow or is scarred as a result of previous

pancreatic inflammation, the graft should be tunneled ante-

rior to the pancreas to ensure that it is not compressed and

to avoid causing bleeding from disrupted pancreatic veins.17

If a prepancreatic tunnel is required, an autogenous conduit

should be considered because the graft will be lying adjacent

to the posterior wall of the stomach. If both the celiac artery

and the SMA are to be revascularized from the supraceliac

aorta, a bifurcated prosthetic graft is attached to the suprace-

liac aorta proximally, with one distal limb anastomosed to the

hepatic artery and the other to the SMA [see Figure 5b].

Retrograde bypass In a retrograde bypass, the infrarenal

aorta or, more commonly, common iliac artery is used as the

inflow vessel. One clear advantage of this procedure is that

the approach to the infrarenal aorta is more familiar to most

surgeons. Another is that dissection and clamping of the infra-

renal aorta are less risky than dissection and clamping of the

supraceliac aorta. Yet another is that the surgeon can work

within a single operative field. Once the self-retaining retrac-

tor is placed, the operation on the infrarenal aorta and the

SMA can be performed without further adjustment of the

retractor. The main disadvantage is the potential for graft

kinking.

Step 1: incision and initial approach Here, too, a midline

incision and a transperitoneal approach are preferred. The

transverse mesocolon is retracted upward, and the ligament

of Treitz is divided.

Step 2: exposure After division of the ligament of Treitz,

the duodenum and the small bowel are retracted to the right.

The SMA may then be identified arising from beneath the

inferior border of the pancreas. The retroperitoneum is

divided distally along the aorta to a point just beyond the

level of the aortic bifurcation. The distal aorta and both

common iliac arteries are assessed to allow determination of

the optimal location for the proximal anastomosis.

Step 3: choice of graft As a rule, grafts made of Dacron or

of ringed, reinforced expanded polytetrafluoroethylene

(ePTFE) are preferred. Problems may arise when retrograde

bypasses are performed with autologous vein grafts, in that

such grafts are prone to kinking when the viscera are replaced.

When a retrograde vein bypass is performed, the graft may bebrought straight up from the right iliac artery so that it lies

between the aorta and the duodenum and then anastomosed

to the posteromedial wall of the SMA.

Step 4: anastomosis to infrarenal aorta or common iliac artery

and SMA Our preference is to use the area near the junction

of the aorta with the right common iliac artery for the proxi-

mal anastomosis. (Short grafts originating from the midpor-

tion of the infrarenal aorta, although commonly described,

are prone to kinking when the viscera are returned to their

normal position.) The graft to the SMA is passed cephalad,

turned anteriorly and inferiorly 180°, and anastomosed to the

anterior wall of the SMA just beyond the inferior border of

the pancreas.17 In this manner, a gentle C loop is formed that,

if placed correctly, keeps the graft from kinking when the

viscera are restored to their anatomic position after retractorremoval [see Figure 6 ]. The ligament of Treitz and the parietal

and mesenteric peritoneum are closed over the graft to

exclude it from the peritoneal cavity.

Endovascular Techniques

Endovascular techniques, usually a combination of angio-

plasty and stent placement, are being used with greater

frequency for chronic mesenteric ischemia [see Figure 7 ]. By

2002, endovascular procedures (angioplasty/stent) surpassed

all surgical procedures performed for chronic mesenteric

ischemia, with decreased 30-day mortality compared with

open procedures (4 versus 13%).18 Early reports describing

the use of percutaneous transluminal angioplasty (PTA) to

treat visceral atherosclerotic lesions indicated that initial tech-

nical success rates were as high as 80% but that recurrence

rates ranged from 20 to 40%.17,19 Recent reports of endovas-cular therapy for chronic mesenteric ischemia showed no

difference in in-hospital morbidity or mortality or 2-year sur-

vival. Also, there was no difference in symptomatic (23 versus

22%) or radiographic (32 versus 37%) recurrence. However,

radiographic primary patency (58 versus 90%) and primary

assisted patency (65 versus 96%) were significantly lower


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in the patients who received endovascular treatment.20

Another study with longer follow-up showed 3-year actuarial

patency of 63%. About 30% of patients required reinterven-

tion for recurrent symptoms. The median time to reinterven-

tion for symptom recurrence was 15 months. Because of thishigh rate of restenosis and symptom recurrence, close follow-

up is mandatory in all patients treated with mesenteric artery

stents. Most importantly, initial endovascular treatment did

not preclude any future surgical bypass options.21 These early

results indicate that an endovascular approach to chronic

mesenteric ischemia is a viable option in carefully selected

patients.

Technical

The main technical complication of mesenteric bypass is

acute graft thrombosis. This event is rare, but when it occurs,

prompt recognition is essential to prevent intestinal infarc-

tion. Kinking and compression of the graft are the most

common causes of this condition. If the retrograde graft is toolong, the redundancy makes it more susceptible to kinking.

Similarly, if the graft is not positioned so as to form a gentle

C loop, it is at risk for kinking when the viscera are returned

to their normal position. An antegrade graft that is too long

is equally at risk for kinking and occlusion. When an ante-

grade bypass is tunneled behind the pancreas, an adequate

amount of space must be present to ensure that the graft

is not compressed. In general, prosthetic grafts are more

resistant to kinking and compression than vein grafts are.

Identification of perioperative graft occlusion is hindered

by postoperative incisional pain, fluid shifts, fever, and leuko-cytosis, all of which are common in the postoperative period

and may mask signs of intestinal ischemia. Patients with

chronic mesenteric ischemia often have symptoms only when

eating and thus may be asymptomatic in the postoperative

period until they resume oral feeding. For these reasons,

we advocate evaluating the graft early in the postoperative

period with either conventional contrast angiography or CT

angiography [see Outcome Evaluation, below].

Additional technical complications may occur as a result

of clamp placement. Clamping of the supraceliac aorta can

lead to renal atheroemboli or ischemia. These problems can

be minimized by using a supraceliac clamp only on an

angiographically normal aorta.

Systemic

Myocardial infarction is the most common cause of mor-tality in patients treated for mesenteric ischemia. Pulmonary

compromise is also a common systemic complication of mes-

enteric revascularization. Renal failure after mesenteric revas-

cularization is more common in patients with preoperative

renal insufficiency.22 Mortality is markedly increased when

renal failure occurs postoperatively.22 Postoperative renal

Figure 5 Arterial bypass: antegrade. Shown is bypass from the supraceliac aorta to the superior mesenteric artery (SMA) alone

(a) or to the hepatic artery and the SMA (b).39

a b


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insufficiency can be minimized by administering mannitol,

furosemide, and, possibly, vasodilators intraoperatively.

Patients who undergo mesenteric revascularization occa-

sionally experience a profound reperfusion syndrome

manifested by acidosis, pulmonary compromise, and coagu-

lopathy. We recommend administering sodium bicarbonate

(to minimize the effects of metabolic acidosis) and mannitol

(for its free radical–scavenging properties) before restoring

intestinal perfusion.

Restoration of pulsatile flow to the small bowel usually

results in immediate active peristalsis and intestinal edema.

The technical success of surgical revascularization is assessed

intraoperatively through visual examination of the intestine

and continuous-wave Doppler examination of the distal

mesenteric vasculature and the bowel wall. Doppler signals

should be detected along the antimesenteric border, and

pulses should be palpable in the mesentery. Intraoperativeduplex scanning may also be used to visualize anastomotic

sites directly.23

Electromagnetic flow measurements can be helpful in

evaluating the adequacy of mesenteric revascularization. Such

measurements must be made after all packs and retractors

have been removed. In most cases, the flow rate through the

graft should be between 500 and 800 mL/min, but flow rates

as high as 1,000 mL/min may be recorded.17

To confirm technical success after mesenteric revascular-

ization, we advocate routine postoperative imaging of the

graft. Ideally, this is done early in the postoperative period.

Catheter-based contrast angiography is optimal for evaluating

the bypass graft and the distal vasculature, allowing identifi-

cation of anastomotic stenoses, kinking [see Figure 8a], or,

in the case of autologous grafts, narrowing caused by valves.

If a technical defect is discovered, reoperation and correction

are required to ensure prolonged patency. In the past few

years, we have started evaluating selected patients periopera-

tively with CT angiography. This modality is less invasive

than traditional contrast angiography but still requires

administration of contrast material and exposure to radiation

[see Figure 8b].

Duplex ultrasonography has been used for postoperative

graft surveillance after mesenteric revascularization.24

Although it can be difficult in the early postoperative period

because of incisional tenderness and postoperative ileus,

it has proven to be a valuable tool to follow bypass grafts.

A retrospective study at our institution has defined normal

duplex ultrasonography–derived velocity characteristics of

mesenteric artery bypass grafts. The anastomotic and mid-graft peak systolic velocities are not affected by the orienta-

tion of the graft. Mean peak systemic velocity for most grafts

is between 140 and 200 cm/s and remains relatively stable on

repeat examinations. Serial duplex examinations can be used

to assess the patency of bypass grafts to mesenteric arteries.25

We routinely use postoperative duplex scanning to establish

Figure 6 Arterial bypass: retrograde. Shown is bypass from

the right common iliac artery to the superior mesenteric

artery.39 The inset shows a method of graft preparation using

the main body of a bifurcated graft to provide a flange for the

proximal anastomosis.

Figure 7 Computed tomographic angiogram showing a stent

in a superior mesenteric artery. Mesenteric artery stents are

being used with increasing frequency as an alternative to

bypass for treatment for chronic visceral ischemia in

higher-risk patients.


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baseline values and to permit comparisons for follow-up

evaluation of graft patency. If markedly elevated focal peak

systolic velocities (> 300 cm/s) are recorded, especially if

they increase on serial examinations, secondary imaging (CT

or conventional angiography) should be obtained to confirm

graft stenosis and to possibly plan intervention.

Procedures for Acute Intestinal Ischemia

As in the evaluation of patients with chronic mesenteric

ischemia, a high index of suspicion is of primary importance

in the evaluation of patients with possible acute mesenteric

ischemia. Most cases of acute intestinal ischemia result either

from thrombosis of a preexisting stenotic lesion or from

embolization (most frequently to the SMA).26 Cardiac emboli

are the most common variety, although tumor emboli27 and

atheroemboli are seen as well. Atheroemboli generally result

from iatrogenically induced cholesterol embolization caused

by aortic catheterization. The prognosis for acute intestinal

ischemia of embolic origin is more favorable than that for

acute ischemia of thrombotic origin. Emboli typically lodge

distally in the SMA distribution; therefore, the proximalintestine is still partially perfused.26 In contrast, thrombotic

occlusion occurs at the origin of the vessel, resulting in

complete interruption of midgut perfusion.

Acute, severe abdominal pain that is out of proportion to

the physical findings is the classic manifestation and is strongly

suggestive of intestinal ischemia. The duration of symptoms

Figure 8 Routine postoperative imaging is performed to confirm technical success after revascularization. (a) A postoperative

arteriogram shows a iliac artery–superior mesenteric artery (SMA) saphenous vein graft with a kink ( arrow). This problem was

asymptomatic and was corrected by reoperation on postoperative day 5. (b) A postoperative computed tomographic arteriogram

shows a retrograde iliac artery–SMA prosthetic graft. C (hook) configuration of distal anastomosis provides antegrade flow into

the SMA.

a b


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does not appear to correlate with the degree of intestinal

infarction.28 Peritonitis is initially absent, but vomiting and

diarrhea may be present, and occult gastric or rectal bleeding

may be identified in as many as 25% of patients.28

There are no reliable serum markers for acute intestinal

ischemia. Leukocytosis, hyperamylasemia, or elevated lactate

levels may be present, but these findings are insensitive and

inconsistent. Abdominal radiographs may reveal dilated

bowel loops and, occasionally, thickened bowel wall, but

these findings are similarly inconsistent. In theory, duplex

ultrasonography may be helpful, but in practice, its applica-

bility is often limited by the gaseous visceral distention

frequently associated with acute intestinal ischemia.

Acute intestinal ischemia is a true surgical emergency. Any

evidence of acute abdomen should result in prompt operative

intervention. In stable patients suspected of having acute

mesenteric ischemia, the paradigm for diagnostic workup

has been slowly shifting toward the use of multidetector CT

angiography. Multidetector CT angiography uses thinner

collimation and overlapping data acquisition, which reduces

the amount of volume averaging and creates higher quality

volume sets for three-dimensional reconstruction. There

are several advantages to CT angiography, including near-

universal 24-hour access to a high-resolution scanner. With

three-dimensional reconstruction, mesenteric vessels can be

evaluated for embolus or thrombotic occlusion with accuracy.

Also, bowel can be evaluated concomitantly to support or

refute the diagnosis, and other intra-abdominal pathology can

be evaluated. A prospective study compared preoperative

radiographic findings with operative findings in 62 patients

suspected of acute myocardial infarction. Initial radiologist

interpretation had a sensitivity of 100% and a specificity of

89%.29 A subsequent study using CT angiography had similar

results in terms of accuracy.30 Significant limitations include

the need for proper timing of the contrast to evaluate

the vasculature and that the modality does not offer any

therapeutic options.

The use of preoperative arteriography to diagnose acute

ischemia is controversial. Delaying treatment to perform

arteriography could result in further intestinal infarction.Angiography may be considered in patients who have abdom-

inal pain without any other signs or symptoms of systemic

illness [see Figure 9 ]. In patients who have rebound tender-

ness, rigidity, or evidence of toxicity or shock, emergency

exploration is indicated.

Patients with acute intestinal ischemia who present with

evidence of toxicity must be resuscitated expeditiously to

ensure that surgical intervention is not delayed. Once it

is determined that surgery is indicated, no further delay is

justified. The patient is placed supine on the operating table,

and the entire abdomen and both legs are prepared. As in

operative treatment of chronic intestinal ischemia, the possi-

bility that autologous vein will be needed for bypass grafting

must be anticipated.

Intraoperative Considerations

Mesenteric revascularization and bowel resection

The goals of surgical therapy are to restore normal pulsatile

inflow, to ensure that questionably viable bowel is adequately

perfused, and to resect any clearly nonviable bowel. During

abdominal exploration, the viability of the intestine and the

status of the blood flow to the SMA are assessed with an eye

to determining the appropriate treatment. The surgeon should

be prepared to perform both intestinal revascularization and

intestinal resection. Segments of clearly viable bowel are often

interspersed with segments of marginally viable bowel and

segments of necrotic bowel. Acutely ischemic bowel that is

not yet necrotic may appear deceptively normal. Mildly to

moderately ischemic bowel may exhibit loss of normal sheen,

absence of peristalsis, and dull-gray discoloration. Other

objective signs of ischemia are the absence of a palpable pulse

in the SMA or in its distal branches, the absence of visible

pulsations in the mesentery, and the absence of flow on

continuous-wave Doppler examination of the vessels of the

bowel wall. The small bowel may be deeply cyanotic yet still

viable. In most cases, bowel resection should not be performed

until after revascularization.

The distribution of ischemic changes provides valuable

information about the cause of the ischemia. SMA thrombo-

sis often results in ischemia to the entire small bowel, with

the stomach, the duodenum, and the distal colon spared; in

severe cases, however, the entire foregut may be ischemic.

In contrast, ischemia secondary to SMA embolism generally

spares the stomach, the duodenum, and the proximal jeju-

num because the emboli tend to lodge at the level of the

middle colic artery rather than at the origin of the SMA. The

choice of operation for revascularizing the bowel depends onthe underlying causative condition. Embolectomy is indicated

for arterial embolism, whereas bypass is indicated for throm-

botic occlusion.

Revascularization of the acutely ischemic intestine

Patients with very advanced intestinal ischemia may have

Figure 9 Preoperative arteriogram shows embolic occlusion

of the superior mesenteric artery distal to its origin.


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obvious widespread bowel necrosis. This situation almost

invariably proves fatal; thus, revascularization is not likely

indicated. In many patients, however, substantial portions of

the bowel are ischemic but not frankly necrotic. Whether

such bowel segments can be restored to viability cannot be

accurately predicted. In most instances, therefore, revascular-

ization should precede resection.

Restoration of normal flow to the SMA can produce

remarkable changes in an ischemic bowel. Because these

changes do not always occur immediately, it is often neces-

sary to preserve questionably viable portions of the bowel

initially and then perform a second-look laparotomy within

12 to 36 hours. If the questionably viable bowel is not in

significantly better condition at the time of the second-look

operation, it should be resected. Occasionally, however, even

a third look is prudent. Revascularized intestine that was

profoundly ischemic may swell dramatically. Temporary

abdominal closure with mesh or leaving the abdomen open

with a temporary closure device may permit tension-free

abdominal “closure,” prevent abdominal compartment syn-

drome, and perhaps even improve intestinal perfusion by

reducing intra-abdominal pressure.

Superior Mesenteric Artery Embolectomy

Step 1: incision and initial approach A midline

incision and transperitoneal approach is used.

Step 2: exposure of SMA at root of mesentery The

SMA is exposed after division of the ligament of Treitz at the

base of the transverse colon mesentery. The duodenum and

the small bowel are retracted to the right [see Figure 10 ]. The

visceral peritoneum is incised above the ligament of Treitz,

just cephalad to the third portion of the duodenum. The SMA

should be readily palpable in this location as it crosses over the

third portion of the duodenum. The dissection is continued to

obtain sufficient proximal and distal control of the vessel.

Heparin is administered, and the vessel is clamped proximally

and distally.

Step 3: arteriotomy An arteriotomy is then made in theSMA. The incision may be either transverse or longitudinal.

We prefer to perform a longitudinal arteriotomy if there is any

possibility that a bypass graft may be needed. The arteriotomy

should be made approximately 2 to 3 cm distal to the origin of

the SMA, although alternative placements may be appropriate

on occasion, depending on the anatomy and the estimated

location of the occlusion [see Figure 11, a and b].

Step 4: embolectomy Proximal embolectomy should be

performed first to ensure adequate inflow. A 3 or 4 French

balloon catheter is sufficient in most cases. If very good pulsa-

tile inflow is not achieved after embolectomy, then thrombosis

of a stenotic lesion is likely to be the underlying cause of the

acute intestinal ischemia, and a bypass graft should be placed.

Even when inflow is apparently adequate, a bypass should

be strongly considered if the proximal SMA is palpably

abnormal.

The narrowness and fragility of the distal SMA and its

branches can make distal embolectomy particularly challeng-

ing. It is best to use a 2 French embolectomy catheter for this

procedure. The catheter must be passed gently, without

undue force.

Step 5: closure Once all possible thrombus has been

removed, the arteriotomy is closed. A transverse arteriotomy

may be closed primarily with interrupted monofilament

sutures [see Figure 11c]; however, a longitudinal arteriotomy

frequently must be closed with an autologous vein patch. If

adequate flow is not restored after the clamps are removed,

the arteriotomy is used as the distal anastomotic site of a

bypass graft.

Superior Mesenteric Artery Bypass

Patients with SMA thrombosis who are seen early enough

and who have no intestinal necrosis may undergo SMA

bypass grafting with a prosthetic conduit. At exploration,

many of these patients have fluid within the peritoneal cavity.

This finding is not, in itself, a contraindication to the use

of a prosthetic graft. However, if the patient has necrotic

bowel that must be resected or if perforation has occurred,

a prosthetic graft should not be used. In these situations, an

autologous vein graft is preferred. A good-quality vein is

mandatory; if the saphenous vein is inadequate, the femoral

vein may be used instead.

The techniques of mesenteric bypass for acute intestinal

ischemia are identical to those for chronic intestinal ischemia.

Because these patients are often acutely ill, it is vital toperform the operation rapidly and efficiently. In the acute

setting, bypass to the SMA alone is strongly preferred [see

Figure 12]. As a rule, a retrograde approach, using the infra-

renal aorta or a common iliac artery for inflow, is best; the

supraceliac aorta is used for inflow only if the infrarenal

vessels are unsuitable for this purpose. Even highly calcified

iliac arteries can be used for inflow provided that there is no

significant pressure gradient and that the surgeon is familiar

with intraluminal balloon occlusion techniques for proximal

and distal control.

Hybrid Technique: Retrograde Open Mesenteric Stenting

Recently, a hybrid technique has been described that

combines the attributes of both endovascular and open

procedures. It allows for both endovascular treatment of mes-

enteric vessels and thorough assessment of bowel viability.

Initial results show a 100% initial success and a lower

in-hospital mortality rate of 17% compared with surgical

bypass or endovascular treatment.31,32

Step 1: Incision and exposure A patient suspected of

acute myocardial infarction is brought directly to the operat-

ing room with ongoing resuscitation. The left arm is abducted

and prepared along with standard preparation for potential

brachial access. Once the diagnosis is confirmed, initial mid-

line exploration and control of the infracolic SMA is obtained

as described for an SMA embolectomy procedure.

Step 2: Patch angioplasty and cannulation of infra-

colic SMA Once exposure and control of infracolic SMA

are obtained, the patient is fully heparinized to activatedclotting time of more than 300 seconds. The artery is incised

longitudinally, and a local thromboendarterectomy with patch

angioplasty is performed. Either bovine pericardium or saphe-

nous vein can be used for the patch. A purse-string suture is

placed in the patch, through which a 6 French sheath is placed

into the SMA in retrograde fashion through the distal end of


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SMA

DividedLigament of Treitz

IMA

Figure 10 Superior mesenteric

artery (SMA) embolectomy.

Exposure of the infrarenal aorta,

proximal right common iliac

artery, and proximal SMA is

achieved by intestinal retraction

and division of the posterior

peritoneum, ligament of Treitz,

and base of small bowel

mesentery.40 IMA = inferior

mesenteric artery.

a

b c

Figure 11 Superior mesenteric artery (SMA) embolectomy.

(a) The location of embolus within the SMA is identified.

(b) Transverse (as shown) or longitudinal arteriotomy is

performed, and the embolus is extracted with a balloon

catheter. (c) Arteriotomy is closed. Primary closure (as

shown) suffices for transverse arteriotomy, but a vein patch is

usually required for closure of longitudinal arteriotomy.40


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the patch. This allows for placement and removal of the sheath

without clamping of the vessel. Once the sheath is in place,

all metal retractors are removed. The sheath should be long

enough to allow the surgeon to work out of the wound and

away from the image intensifier.

Step 3: Crossing the lesion with a guidewire Initially,

hand-injected, retrograde, lateral angiography is performed to

delineate the lesion. This angiogram is used as a road map

to cross the lesion with a 0.035-inch glidewire. This is then

catheter exchanged for a lower profile 0.018- or 0.014-inch

platform.

Step 4: Predilatation and stent deployment The

lesion is then predilated with a 2 or 3 mm angioplasty balloon.

A 5 to 7 mm low-profile balloon-expandable stent is deployedin a retrograde fashion. The proximal-most stent is allowed

to protrude 1 to 2 mm into the aortic lumen. More than one

stent may be required to cross the entire length of the lesion.

Completion angiography in the anteroposterior and lateral

projections and pressure measurements are performed across

the lesion.

Step 5: Sheath removal and assessment of bowel

viability After completion angiography is performed, the

sheath is removed and the puncture site in the patch is

repaired. The entire bowel is thoroughly examined, and

any grossly necrotic bowel is expeditiously resected. Final

assessment and reanastomosis are usually delayed for 24 to

48 hours.

Endovascular Techniques

Purely endovascular techniques have a limited role in the

treatment of acute mesenteric ischemia as they do not offer

assessment of ischemic bowel. General surgical principles of

thorough abdominal exploration, along with sepsis control

and routine second-look operations, must be honored in all

patients with acute mesenteric ischemia to optimize favorable

outcomes. It would seem reasonable that endovasculartherapies might come to play a role in the treatment of acute

intestinal ischemia, given that preoperative angiography is

usually feasible in stable patients. Several groups have reported

treating acute arterial embolism with intra-arterial thrombol-

ysis33,34; others have reported treating acute embolism, as well

as thrombotic occlusion, with PTA.35,36 Although a degree

a b

Figure 12 Superior mesenteric artery (SMA) bypass. (a) Iliac artery–SMA bypass with a prosthetic graft is suitable for cases in

which SMA thrombosis produces ischemic but salvageable bowel. (b) Iliac artery–SMA bypass with a saphenous vein is suitable

for cases in which some segments of necrotic or perforated bowel must be resected.40


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of anecdotal success with these techniques has been achieved

in selected cases, it should be kept in mind that reliance on

endovascular therapy alone for presumed acute intestinal

ischemia runs the risk of missing bowel necrosis. After endo-

vascular therapy, frequent clinical reevaluation is necessary

to identify patients with persistent intestinal ischemia.

Abdominal exploration should be very strongly considered

in most cases, even if the angiographic result of the endovas-

cular procedure is good.

Occasionally, patients present with emboli that have lodged

in the small arterial branches of the SMA. These vessels are

often too small to allow the passage of embolectomy cathe-

ters, and bypass beyond the point of obstruction frequently is

not possible. In these situations, resection of marginally viable

bowel is the best option.

As noted (see above), avoidance of graft kinking is crucial

for preventing early graft failure. Graft failure can have an

even greater adverse effect on bowel viability in the setting

of acute ischemia than in the setting of chronic intestinal

ischemia.

Recovery after revascularization is often prolonged.

Early and prolonged parenteral nutrition may be necessaryin patients with extensive bowel infarction. Only rarely,

however, is lifelong parenteral nutrition required.

The techniques employed to evaluate the success of mes-

enteric revascularization for acute ischemia include clinical

inspection, continuous-wave Doppler ultrasonography,

and intravenous (IV) administration of fluorescein. Clinical

inspection entails visual assessment of pulsatile flow in the

mesenteric arcades, peristalsis, bleeding from cut surfaces,

and, of course, color. In one study, clinical parameters

were found to be 82% sensitive and 91% specific for bowel

viability.37

We routinely use a sterile continuous-wave Doppler ultra-

sonography to evaluate pulsatile flow on the bowel surface.Grossly discolored bowel with no Doppler signal after a

period of observation should be resected; marginal bowel

with no Doppler signal is an indication for second-look

laparotomy.

With the fluorescein fluorescence method, 10 to 15 mg/kg

of fluorescein is injected intravenously, and the intestine is

inspected with a Wood lamp. A complete absence of fluores-

cence is diagnostic of nonviability; rapid, confluent, bright

fluorescence indicates viability. There is, however, a large

gray area between these two extremes in which interpretation

is subjective. In one study, the IV fluorescein method was

found to be 100% sensitive and specific for detecting non-

viable bowel.38 The disadvantages of this technique are that

it requires special equipment and that it exposes the critically

ill patient to the risk of an adverse reaction to the dye.Other assessment methods (e.g., surface oximetry, infrared

photoplethysmography, and laser Doppler velocimetry) are

available, but at present, they are mostly experimental and

are not in general use for evaluation of bowel viability in a

clinical setting.

Financial Disclosures: None Reported

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Acknowledgment

Figures 5, 6, 10, 11, and 12 Alice Y. Chen


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