Acs0604 Acute Mesenteric Ischemia

© 2005 WebMD, Inc. All rights reserved. ACS Surgery: Principles and Practice
6 VASCULAR SYSTEM 4 ACUTE MESENTERIC ISCHEMIA — 1

4 ACUTE MESENTERIC ISCHEMIA
Melina R. Kibbe, M.D., and Heitham T. Hassoun, M.D.

Diagnosis and Management of Acute Bowel Ischemia

Acute mesenteric ischemia is an uncommon life-threatening clin- 68% presented with vague abdominal pain. Other presenting
ical entity that ultimately leads to death unless it is diagnosed and symptoms included diarrhea (42%), nausea and vomiting (32%),
treated appropriately. Despite diagnostic and therapeutic advances malaise (16%), and upper GI bleeding (10%).2
and an improved understanding of the pathophysiology, the mor- In addition to the clinical presentation, risk factors provide
bidity and mortality associated with acute mesenteric ischemia essential clues for correct identification of these disease processes.
remain high, having changed relatively little over the past several Certain general risk factors for acute mesenteric ischemia have
decades. Accordingly, the index of suspicion for this disease should been identified. In one study, 78% of the patients presented with
be high whenever a patient presents with acute-onset severe a history of hypertension, 71% with a history of tobacco use, 62%
abdominal pain that is out of proportion to the physical findings. with a history of peripheral vascular disease, and 50% with a his-
Once the diagnosis is made, prompt intervention is required to tory of coronary artery disease (CAD).1
minimize morbidity and mortality. There are also more specific risk factors for individual causes of
Acute mesenteric ischemia can result from any of four distinct acute mesenteric ischemia. Patients with embolic occlusion of the
processes: (1) embolic occlusion of the mesenteric circulation mesenteric circulation typically have a history of recent cardiac
(usually the superior mesenteric artery [SMA]); (2) acute throm- events (e.g., myocardial infarction, atrial fibrillation, mural throm-
bosis of the mesenteric circulation; (3) intense splanchnic vaso- bus, mitral valve disease, or left ventricular aneurysm) or previous
constriction—so-called nonocclusive mesenteric ischemia embolic disease. In the study just cited, 50% of the patients who
(NOMI)—which is usually associated with a low-flow state or pro- presented with embolic occlusive disease had atrial fibrillation.1
found hypovolemia; or (4) mesenteric venous thrombosis (MVT). Patients with acute mesenteric ischemia secondary to thrombotic
occlusive disease typically have other manifestations of diffuse
atherosclerotic disease (e.g., CAD, peripheral artery disease, and
Clinical Evaluation carotid stenosis).The risk factors for NOMI are slightly different.
This condition usually occurs during severe low-flow states and
HISTORY AND PHYSICAL EXAMINATION
represents extreme mesenteric vasoconstriction. It is much more
The classic presentation for patients common among severely ill patients in an intensive care unit who
with embolic disease of the mesenteric require vasopressors and among patients undergoing dialysis with
vessels is sudden-onset midabdominal excessive fluid removal.The risk factors for MVT include a histo-
pain that is described as being out of pro- ry of previous venous thrombosis or pulmonary embolism, a
portion to the physical findings and is known or suspected hypercoagulable state, oral contraception,
associated with immediate bowel evacu- and estrogen supplementation. In a study of 31 patients who pre-
ation. In fact, only about one third of sented with MVT at Northwestern University, 13 (42%) were
patients present with the triad of abdominal pain, fever, and diagnosed with a hypercoagulable state, six (19%) had a history
heme-positive stools. A study that considered all causes of acute of previous thrombotic episodes, and four (13%) had a history of
mesenteric ischemia found that 95% of patients presented with cancer.2
abdominal pain, 44% with nausea, 35% with vomiting, and 35%
with diarrhea1; only 16% presented with blood per rectum.
Patients with thrombotic mesenteric occlusion also present Investigative Studies
with sudden-onset severe midabdominal pain that is out of pro- Although there are no basic laboratory or radiographic studies
portion to the physical findings, but unlike patients with acute that are diagnostic for acute mesenteric ischemia, such studies can
embolic occlusion, they typically have a history of chronic post- help confirm the diagnosis when it is suspected on the basis of the
prandial abdominal pain and significant weight loss. history and the physical examination.
Patients with NOMI present somewhat differently. The pain
LABORATORY TESTS
reported is usually not as sudden as that noted with embolic or
thrombotic occlusion: it is generally more diffuse and tends to In most cases, the white blood cell count is elevated. In a study
wax and wane (unlike the pain associated with embolic or throm- from the Mayo Clinic, 98% of patients who presented with acute
botic disease, which tends to get progressively worse). mesenteric ischemia were found to have an elevation of the leuko-
Patients with MVT often present with various nonspecific cyte count, and 50% were found to have counts higher than
abdominal complaints; accordingly, this diagnosis may be espe- 20,000/mm3.1 Lactate is another nonspecific indicator of mesen-
cially challenging. Common complaints include nausea, vomit- teric bowel ischemia. In the same Mayo Clinic study, approxi-
ing, diarrhea, abdominal cramping, and nonlocalized abdominal mately 91% of patients had elevated lactate levels, with 61% hav-
pain. As a rule, these symptoms are not acute. A study of MVT ing levels higher than 3 mmol/L.1 In addition, 71% of patients
patients found that 84% presented with abdominal pain.2 Of presented with an elevated AST, whereas 52% presented with an
those 84%, only 16% presented with peritoneal signs, whereas abnormal base deficit.1
1


Diagnosis and Management of
Acute Bowel Ischemia

Patient presents with severe abdominal pain consistent with
ischemic bowel

Obtain history and perform physical examination. Pain that is out of proportion
to physical findings is a significant clue.
Look for risk factors for acute mesenteric ischemia.
Order investigative studies:
• Laboratory tests: WBC count, lactate, AST
• Imaging: abdominal x-ray, duplex ultrasonography, CT angiography, MRA

Acute mesenteric ischemia is suspected

Perform contrast angiography (anteroposterior
and lateral views; early and delayed images) to
confirm diagnosis.

Specific disorder is identified

Manage underlying disorder as appropriate.

Patient has embolic disease Patient has thrombotic disease Patient has nonocclusive Patient has mesenteric
mesenteric ischemia (NOMI) venous thrombosis (MVT)
Treat with surgical embolectomy Perform mesenteric bypass,
and anticoagulation. either antegrade (from supraceliac Correct underlying condition. Treat with anticoagulation.
Consider catheter-directed aorta to SMA) or retrograde Optimize fluid status, improve Consider catheter-directed
intra-arterial thrombolysis. (from infrarenal aorta or iliac cardiac output, and eliminate thrombolysis.
artery to SMA). pressors. Perform hypercoagulability
Assess bowel for possible
resection. Assess bowel for possible Consider catheter-directed intra- workup.
resection. arterial infusion of papaverine,
30–60 mg/hr. Assess therapy
with repeat angiography.

No bowel resection was Bowel resection was required,
required, and bowel is or there is marginally perfused
viable after revascularization bowel after revascularization
Patient improves and Patient does not improve
shows no signs of bowel or shows signs of bowel
Perform second-look exploratory ischemia ischemia
laparotomy.

Perform exploratory laparotomy,
and resect any frankly necrotic
bowel.
Perform second-look exploratory
laparotomy to assess viability of
any marginally perfused bowel.


IMAGING diagnosis of acute mesenteric ischemia than duplex ultrasonogra-
phy is. Both CT and MRA have undergone significant advances
Abdominal X-rays over the past decade. Traditional CT scanning can evaluate arte-
Although abdominal radiographic films can neither establish rial patency and anatomy and detect calcifications and
nor exclude the diagnosis of acute mesenteric ischemia, they may aneurysms. In addition, it can evaluate the status of the bowel and
reveal signs that are consistent with bowel ischemia. If obtained help identify other causes of abdominal pain (e.g., pancreatitis,
early, abdominal plain films should show no abnormalities. If bowel perforation, and bowel obstruction). However, it was not
obtained late in the presentation, however, they may reveal edem- until the advent of helical (spiral) CT scanning—and, subse-
atous bowel with thumbprinting. In severe cases, abdominal plain quently, of multislice, multiarray helical CT scan technology with
films may reveal gas in the bowel wall and the portal vein. More maximum-intensity projection—that the visceral arterial anatomy
commonly, however, they reveal a pattern consistent with ileus or could be visualized with three-dimensional spatial resolution [see
are completely unremarkable. In a study of patients operated on Figure 1]. This technology allows much more rapid acquisition of
for acute mesenteric ischemia, mortality was 29% in patients with data and thereby improves the quality of vascular imaging tremen-
normal plain radiographic films, compared with 78% in those dously. A study comparing spiral CT angiography with conven-
with abnormal films.3 Nevertheless, it must be emphasized that tional contrast angiography found that the former had a sensitiv-
the primary role of abdominal plain radiographic films in this set- ity of 75% and a specificity of 100% for the detection of greater
ting is to exclude other identifiable causes of abdominal pain (e.g., than 75% stenosis of the celiac artery.5 Furthermore, spiral CT
obstruction and perforation with free air). angiography had a sensitivity of 100% and a specificity of 91% for
the detection of SMA stenosis.
Duplex Ultrasonography Although CT technology has become much more sophisticated
Duplex ultrasonography plays only a limited role in the man- and the image clarity and definition have improved greatly, there
agement of acute mesenteric ischemia—not surprisingly, given are still limits to what can be determined by means of CT in the
the acute nature of the presentation, the accompanying ileus with setting of acute embolic or thrombotic disease. The origins of the
excessive bowel gas and bowel edema (which hinders visualization celiac artery and the SMA are well visualized with CT, but sec-
of the mesenteric vessels), and the reduced access to the vascular ondary, tertiary, and smaller branches are less well defined; for visu-
laboratory during off hours. Furthermore, duplex ultrasonogra- alizing these branches, contrast angiography remains the gold stan-
phy, though capable of imaging stenotic and occlusive lesions at dard [see Contrast Angiography, below]. Another limitation of cur-
the origin of a mesenteric vessel, is of no value in detecting emboli rent CT scanning technology is the need to administer intravenous
beyond the proximal portion of the vessel. Similarly, it has no role contrast agents, which can be nephrotoxic or, in some patients, trig-
in the diagnosis of NOMI. ger contrast allergies. CT angiography also tends to overestimate
Duplex ultrasonography does have a definite and well-defined the degree of critical stenosis when compared with conventional
role in the diagnosis of chronic mesenteric ischemia.Well-accept- angiography; however, this limitation appears to be less of an issue
ed published criteria exist for the diagnosis of celiac artery and with the advent of multiarray or multidetector technology, which is
SMA stenosis on the basis of velocity measurements.4 In the diag- more sensitive in detecting arterial stenosis. Finally, significant cal-
nosis of acute mesenteric ischemia, however, where the primary cification at the origin of the vessel can make it difficult to deter-
goal is to determine whether there is an acute occlusion of the mine the true degree of stenosis with CT scanning.
celiac artery or the SMA, the aforementioned technical limita- In contrast to its relatively limited role in the diagnosis of acute
tions of this diagnostic modality limit its application. mesenteric ischemia of embolic or thrombotic origin, CT plays a
valuable role in diagnosing MVT and is the preferred diagnostic
CT Angiography imaging modality in patients presenting with abdominal pain who
Computed tomographic angiography and magnetic resonance have a history of deep vein thrombosis (DVT) or a known hyper-
angiography (MRA) are more commonly used to confirm the coagulable disorder.6 CT scanning can readily reveal thrombosis

a b c

Figure 1 Shown are CT scans of mesenteric vessels: (a) transaxial image of celiac artery (arrow); (b) transaxial image of SMA
(arrowhead); and (c) three-dimensional reconstruction of aorta and origins of celiac artery (arrow) and SMA (arrowhead).


a b

Figure 2 (a) CT scan shows partially occluding thrombus in SMV (arrow). (b) CT scan obtained 4 months
later reveals complete resolution of thrombus (arrowhead).

Magnetic Resonance Angiography
of the superior mesenteric vein (SMV), with or without associat-
ed bowel abnormalities [see Figure 2]. In fact, CT scans of SMV Advances in magnetic resonance technology—in particular, the
thrombosis in asymptomatic patients have provided useful infor- development of contrast-enhanced three-dimensional MRA—
mation on the pathophysiology of MVT and broadened our have made MRA imaging of visceral vessels much more practical
understanding of the wide spectrum of this disease entity. In a than was once the case. Fast imaging techniques using I.V. admin-
study from the Mayo Clinic, CT scanning correctly identified istration of gadolinium over a single breath-hold can provide high-
100% of patients who presented with acute MVT and 93% of quality three-dimensional images [see Figure 3] in axial, sagittal, or
those who presented with chronic venous thrombosis.7 In a sub- oblique planes. An advantage MRA has over CT angiography is
sequent study from our institution (Northwestern University), that gadolinium is significantly less nephrotoxic than the contrast
CT scanning identified 100% of MVT patients who presented agents used for CT scans. Like CT angiography, however, MRA
with vague abdominal pain or diarrhea and 90% of MVT patients does not adequately assess the distal branches of the mesenteric
who underwent a CT scan.2 In contrast, conventional angiogra- vessels. One study compared contrast-enhanced breath-hold
phy correctly diagnosed MVT in only five of nine patients.2 MRA with conventional digital subtraction angiography in 33
patients.8 There was excellent agreement between the two studies
for the celiac artery and the SMA; however, there was poor agree-
a b ment for the distal branches of the SMA, as well as for the intra-
hepatic branches of the hepatic artery.
Given the current state of imaging technology, it is possible to
confirm the diagnosis of acute mesenteric ischemia with either
CT angiography or MRA. If the cause of the ischemia is con-
firmed—and, in the case of SMA thrombosis, if distal targets are
identified for revascularization—it is conceivable that the patient
could be explored in the OR without undergoing conventional
angiography. Many institutions, however, do not have ready
access to all the latest imaging technology. In such situations, the
best imaging modality for evaluation of the mesenteric vascula-
ture remains contrast angiography.
Contrast Angiography
Contrast angiography has long been
considered the gold standard for imag-
ing the visceral vessels. This modality
can visualize the aorta and the main
trunks of the mesenteric vessels and can
adequately assess several orders of distal
branches. The images obtained with
contrast angiography are superior to
Figure 3 Shown are contrast-enhanced three-dimensional those obtained with CT angiography or
MRAs of aorta and mesenteric vessels. (a) Anterior projection MRA. The procedure is performed in a transfemoral manner by
shows celiac artery (arrow) and SMA (arrowhead). (b) Lateral means of the Seldinger technique, with infusion of approximately
projection shows celiac artery (arrow) and SMA (arrowhead). 60 to 100 ml of contrast material. Arteriography should include


both anteroposterior and lateral views of the celiac artery, the
SMA, and the inferior mesenteric artery (IMA). The origins of
the celiac artery and the SMA are best seen on the lateral view,
whereas the middle and distal SMA and the IMA are best seen on
the anteroposterior view. Delayed views are useful in evaluating a
patient for NOMI.
There are classic angiographic patterns that serve to distinguish
mesenteric ischemia of embolic origin from that of thrombotic
Aorta origin [see Figure 4]. Of the three mesenteric vessels, the SMA is
Usual Site most likely to be the site of embolic lodgment because it takes off
of Thrombosis
from the main axis of the aorta at a less sharp angle than the celi-
ac artery and the IMA, which arise from the aorta more perpen-
dicularly.When emboli lodge in the SMA, they usually lodge dis-
tal to the middle colic branch and the jejunal branch [see Figure
5]. In thrombotic disease, the thrombus usually forms at the ath-
Usual Site of erosclerotic plaque, which, for most patients, is usually at the ori-
Embolization gin of the mesenteric vessel. Consequently, the angiogram typi-
cally demonstrates complete absence of flow in the mesenteric
Superior
Mesenteric vessel, which often makes it difficult to ascertain the location of
Artery the vessel’s origin [see Figure 6].
Patients with NOMI typically exhibit angiographic evidence of
SMA vasospasm. A small SMA trunk is visualized, with very few
branching vessels visible, and the branches that are visualized
Figure 4 Schematic drawing demonstrates usual site for SMA show a characteristic tapering of the vessel to the point of occlu-
thrombosis versus that for SMA embolus. sion [see Figure 7a]. These patterns are best seen on the antero-
posterior projection.
Angiography is less useful for the diagnosis of MVT. Typically,
MVT is diagnosed on the venous phase of the selective arterial
contrast injection; however, as noted [see CT Angiography, above],
conventional angiography is less sensitive and specific for MVT
than the diagnostic imaging modality of choice—namely, CT.
Besides providing superior image quality, contrast angiography
enables the surgeon to perform selective injection of any of the
mesenteric vessels and to perform therapeutic intervention. In
patients with NOMI, for example, the SMA may be selectively
catheterized and papaverine infused directly into the vessel [see
Figure 7b]. In a stable patient with acute mesenteric ischemia from
a partially occluding embolus but no peritoneal signs, selective
catheterization of the SMA allows the institution of catheter-
directed intra-arterial thrombolytic therapy [see Figure 8]. Thus,
contrast angiography not only represents the gold standard for
diagnostic imaging but also provides important therapeutic options.

Management

TREATMENT OF SPECIFIC DISORDERS

Embolic Occlusion of Mesenteric
Vessels
The goals in the surgical treatment of
acute mesenteric ischemia are (1) to
restore normal pulsatile flow to the
SMA and (2) to resect any nonviable
intestine. In general, revascularization
precedes resection. The therapeutic approach varies, depending
on the specific underlying cause. For embolic disease of the SMA,
the standard treatment is surgical embolectomy; this procedure is
described in more detail elsewhere [see 6:14 Mesenteric Revascu-
larization Procedures].
Percutaneous interventional treatment of acute SMA occlusion
Figure 5 Selective angiogram of SMA in anterior projection has also been described in the literature. At present, however, the
demonstrates embolus within vessel (arrow) at typical location. applicability of this approach is limited, in that most patients pre-


sent with symptoms that warrant an exploratory laparotomy for
evaluation of intestinal viability. In patients who present with
abdominal pain, have no peritoneal signs that would necessitate
an exploratory laparotomy, and are found to have a partially
occluding embolus in the SMA, catheter-directed intra-arterial
thrombolytic therapy is worth considering. We have treated such
patients in this manner at our institution. This route should be
used cautiously, however, and if intra-arterial thrombolytic thera-
py is instituted, the patient should be closely monitored in the
ICU with serial abdominal examinations. Even if thrombolytic
therapy does restore blood flow to the ischemic intestine, the
patient may still experience pain sufficient to necessitate explo-
ration. For these reasons, our use of thrombolytic therapy is high-
ly selective.
Thrombotic Occlusion of Mesenteric
Vessels
Acute mesenteric ischemia secondary
to thrombotic disease occurs in patients
with long-standing atherosclerotic dis-
ease of the mesenteric vessels. In this sit-
uation, the entire midgut is usually
involved. Surgical treatment consists of a
bypass procedure [see 6:14 Mesenteric
Revascularization Procedures], which may
be done in either an antegrade or a retrograde manner. The con-
duit of choice is a reversed autologous greater saphenous vein
graft. Synthetic graft material should be avoided in the setting of
acute bowel ischemia, given the high risk of transmural bowel
infarction and perforation.
There are several different inflow options for revascularizing
the SMA that must be considered carefully.The main choices for
inflow are the supraceliac aorta, the infrarenal aorta, and the iliac
artery. In cases of acute mesenteric ischemia where time is of the
essence and prompt revascularization of the bowel is required, it
is often easier to perform a retrograde bypass from the infrarenal
aorta or iliac artery, in that the exposure is relatively simple and
Figure 6 Lateral contrast angiogram of aorta demonstrates
readily familiar to all vascular surgeons. Furthermore, a retro- complete occlusion of both celiac artery (arrow) and SMA
grade bypass yields less hemodynamic compromise because it (arrowhead) at their origins, consistent with in situ thrombosis.
avoids supraceliac clamping and the associated mesenteric and Lack of collaterals suggests an acute process.
renal ischemia. Accordingly, retrograde bypass is the preferred
approach in our institution. In cases of acute mesenteric ischemia
where the suprarenal aorta is easily approachable and not calci- If the patient presents with peritoneal signs on physical exami-
fied, however, an antegrade vein graft from the suprarenal aorta to nation, an exploratory laparotomy will be required for resection of
the SMA will lie better because it is less susceptible to kinking frankly necrotic or gangrenous bowel. If an intra-arterial infusion
than a retrograde graft once the bowel is restored to its correct of papaverine has been initiated, it should be continued through-
anatomic position. out the exploratory laparotomy. Given the known propensity of
this disease process for waxing and waning, a second-look laparot-
Nonocclusive Mesenteric Ischemia omy is also imperative [see Second-Look Laparotomy, below].
Management of NOMI is largely non-
operative. Once the diagnosis has been Mesenteric Venous Thrombosis
established with angiography [see Figure Once mesenteric venous thrombosis
7], treatment of the underlying precipi- is diagnosed, the mainstay of therapy is
tating cause is the key therapeutic inter- anticoagulation. If the patient’s condi-
vention. Optimization of fluid resuscitation does not improve or worsens after
tion, improvement of cardiac output, anticoagulation or if signs or symptoms
and elimination of vasopressors are the of bowel ischemia (e.g., peritonitis)
measures that have the greatest impact develop, abdominal exploration is war-
on outcome. Selective catheterization of the SMA with direct ranted.Typically, the bowel is dusky and
intra-arterial infusion of papaverine (30 to 60 mg/hr) may be edematous. All frankly necrotic bowel
employed as adjunctive therapy. The infusion is continued for at should be resected. Within 24 to 48
least 24 hours, with repeat angiography performed at regular hours, a second-look laparotomy should be done to evaluate the
intervals to determine the effectiveness of this therapy. viability of any marginally perfused bowel [see Second-Look


a b

Figure 7 Shown are contrast angiograms of aorta and mesenteric vessels in a patient with NOMI. (a)
Selective angiogram (anterior projection) of SMA demonstrates distal spasm of SMA. (b) Selective
angiogram (anterior projection) of SMA after intra-arterial papaverine infusion demonstrates
improved filling of distal branches of SMA.

Laparotomy, below]. In a study of 31 MVT patients from our insti- Once the diagnosis of MVT has been established, a hypercoagula-
tution,2 the majority were successfully treated with anticoagulation bility workup should be performed in an effort to identify the under-
alone and experienced complete resolution of their symptoms; lying cause. If the cause is found to be a hematologic hypercoagula-
however, 32% did require small bowel resection. Perioperative ble state, lifelong anticoagulation is recommended. If the cause is
mortality was 23%. Among those who survived operation, the reversible, anticoagulation may be discontinued after 3 to 6 months.
long-term survival rate was 88%; all of these survivors were symp-
SECOND-LOOK LAPAROTOMY
tom free at last follow-up.
Thrombolytic therapy has also been employed to treat MVT. Second-look laparotomy is an essen-
The catheter may be directed into the SMA for lysis of portal vein tial part of the management of acute
thrombus.2 Alternatively, it may be directed into the SMV or the mesenteric ischemia. No matter which
portal vein intraoperatively.9 adjunctive method is used intraopera-
tively to assess bowel perfusion and via-
a b bility, second-look laparotomy is the
most reliable means of determining the
viability of marginally perfused bowel
after revascularization. A second-look
laparotomy should be preceded by adequate fluid resuscitation
and correction of the acid-base imbalance. Furthermore, the deci-
sion to perform a second-look laparotomy should be made during
the first operation and adhered to no matter what the patient’s
condition is 24 to 48 hours later. Occasionally, even though the
patient is in better physical condition 24 to 48 hours later—large-
ly because of aggressive fluid resuscitation and correction of the
acid-base imbalance—there is still some necrotic bowel that must
be resected. Accordingly, we adhere to a strict policy of planned
reexploration for acute mesenteric ischemia patients who require
bowel resection during the initial operation or who have areas of
marginally viable bowel after revascularization.

Intraoperative Consultation

Figure 8 (a) Selective angiogram of SMA demonstrates partially
Vascular surgeons are frequently consulted intraoperatively to
occluding embolus in distal vessel (arrow). (b) Selective evaluate a patient for acute mesenteric ischemia. Often, the
angiogram after catheter-directed intra-arterial thrombolytic patient has been taken to the OR on an emergency basis for
therapy shows resolution of embolus. acute abdominal pain with peritoneal signs or hemodynamic


Surgeon is consulted intraoperatively for evaluation of acute mesenteric ischemia

Determine whether bowel is salvageable. About 50 cm of viable bowel is required to
sustain life if ileocecal valve is present; 100 cm is preferred.

Bowel is salvageable Bowel is not salvageable

Assess pulses in SMA. Close abdomen.

No pulse is felt in SMA Weak pulse is felt in SMA Normal pulse is felt in SMA

Proximal jejunum and Diffuse midgut bowel NOMI is likely diagnosis MVT is likely diagnosis
transverse colon are spared ischemia is present
from ischemia
Correct underlying condition. Begin anticoagulation immediately.
Optimize fluid status, improve Determine underlying cause.
cardiac output, and eliminate
pressors. Perform hypercoagulability workup.
Embolic disease of SMA is Thrombotic disease of Consider catheter-directed intra- Assess bowel for possible resection.
likely diagnosis SMA is likely diagnosis arterial infusion of vasodilator.
Treat with surgical embolectomy Perform mesenteric bypass, resection.
and anticoagulation. either antegrade (from
Assess bowel for possible supraceliac aorta to SMA) or
resection. retrograde (from infrarenal
aorta or iliac artery to SMA).
resection.

Bowel resection was required, or there is Bowel is viable
marginally perfused bowel after revascularization

Perform second-look exploratory laparotomy.

Figure 9 Algorithm illustrates intraoperative determination of bowel salvageability, evaluation of SMA
pulses, and assessment of bowel viability after revascularization.

instability [see Figure 9]. In the OR, acute mesenteric ischemia INTRAOPERATIVE EVALUATION OF SUPERIOR MESENTERIC
typically presents as diffuse bowel ischemia. The first decision ARTERY
point in the evaluation is the determination of whether the SMA pulses are assessed by palpating the root of the mesen-
bowel is salvageable. tery. The transverse colon is reflected superiorly, and the small
bowel is reflected to the patient’s right. The SMA is then palpat-
DETERMINATION OF BOWEL SALVAGEABILITY
ed by placing four fingers of the hand behind the root of the
If diffuse bowel necrosis exists and the bowel is not salvageable, mesentery, with the thumb opposite and anterior to the root.The
it is best to close the abdomen without attempting further thera- SMA can also be identified by following the middle colic artery
py. Approximately 50 cm of viable bowel is required to sustain life proximally until it enters the SMA. Alternatively, a handheld
if the ileocecal valve is present, and 100 cm is preferable.10 Doppler device may be employed to listen to the quality and char-
Therefore, if it is obvious that no bowel can be preserved, further acter of the arterial signal at the root of the mesentery.
intervention is pointless. If the bowel is salvageable, blood flow to Intraoperative angiography may also be used for evaluation, but it
the bowel must be evaluated by assessing the pulses in the SMA. is often difficult to perform in the OR if there has not been ade-
If no pulse can be detected in the SMA, it is imperative that revas- quate preparation and setup ahead of time, and it may not be fea-
cularization be undertaken before bowel resection. sible in some institutions.


Figure 10 Intraoperative photograph of
patient who presented with acute mesenteric
ischemia secondary to embolus of SMA shows
diffuse bowel ischemia with classic sparing of
proximal jejunum (arrow) and transverse colon
(arrowhead).

If a strong pulse is appreciated throughout the length of the though it may be dilated and edematous when the patient pre-
SMA, MVT is the probable cause of the diffuse bowel ischemia. sents late with frank bowel necrosis.
Once MVT is suspected, I.V. administration of heparin should Within the category of arterial causes of acute mesenteric
immediately follow. If the bowel is viable, the patient should be ischemia, the various underlying conditions are also associated
observed closely for signs or symptoms of deterioration. If the with distinct patterns of bowel ischemia.Typically, in embolic dis-
patient’s condition appears to be deteriorating, reexploration is ease, the small bowel and the proximal colon are affected, and the
indicated, with resection of any frankly necrotic bowel; throm- proximal jejunal segment and the transverse colon are spared [see
bolytic therapy should be considered, and a second-look laparot- Figure 10]; the reason is that the embolus usually lodges just past
omy should be performed. It is important to palpate the SMA the middle colic artery and the jejunal branches of the SMA. If
pulse distally as well as proximally to ensure that the patient does the entire small bowel is diffusely affected, as well as the ascend-
not have an embolus to the distal SMA. ing and transverse colon, the origin of the SMA is probably
If the SMA pulse is weak, the diagnosis of NOMI should be occluded; this disease pattern is consistent with thrombotic occlu-
entertained. The mainstay of therapy for NOMI is treatment of sion of the vessel by underlying atherosclerotic lesions. In NOMI,
the underlying cause, which typically involves fluid resuscitation, the entire small bowel may be affected, but the pattern of
administration of inotropes and calcium channel blockers, and ischemia tends to be patchy, with segmental areas of involvement.
cessation of vasoconstrictors. Catheter-directed intra-arterial
INTRAOPERATIVE ASSESSMENT OF BOWEL VIABILITY AFTER
infusion of papaverine for 24 to 48 hours may be beneficial as
REVASCULARIZATION
well. If bowel resection proves necessary at the time of explo-
ration, it is best to plan on performing a second-look laparotomy, Approximately 10 to 20 minutes after revascularization, the
regardless of the patient’s clinical status 24 to 48 hours after the viability of the intestine should be assessed. Waiting until after
initial exploration. revascularization to assess the extent of irreversible bowel
If there is no SMA pulse at the root of the mesentery, the most ischemia or necrosis requiring resection makes it possible to pre-
likely diagnosis is in situ thrombosis from chronic mesenteric serve more bowel length. After restoration of flow, the bowel may
arterial disease [see Figure 4]. If the SMA pulse is palpable proxi- contain frankly necrotic areas, normal areas, and marginally per-
mally but not several centimeters distally, the likely diagnosis is an fused areas. Obviously, clearly necrotic or nonviable bowel must
embolus to the SMA [see Figure 4]. Distinguishing between these be resected at the time of the operation. Determination of the via-
two conditions is important because their surgical treatments dif- bility of marginally perfused bowel is more difficult.
fer significantly. To make this distinction correctly, the surgeon Intraoperatively, the color, motility, and integrity of the bowel
should be aware of how the patient presented, whether the patient should be evaluated. The characteristic appearance of ischemic
experienced postprandial abdominal pain for an extended period bowel includes loss of the normal sheen, dull-gray discoloration,
before the acute presentation, and whether the patient has other and lack of peristalsis. Determination of the character and quali-
risk factors of arterial occlusive disease [see Clinical Evaluation, ty of the pulses in the antimesenteric border and the mesenteric
above]. In addition, the surgeon should be aware of the specific arcades may help determine which areas of the bowel will remain
pattern of bowel ischemia present. viable once revascularization has been performed. Intraoperative
Doppler assessment of bowel perfusion may be performed with a
DIFFERENTIATION OF PATTERNS OF BOWEL ISCHEMIA
sterilized continuous-wave Doppler ultrasound flow detector.The
The different causes of acute mesenteric ischemia are associat- probe is placed on the antimesenteric border of the intestine to
ed with different classic patterns of bowel ischemia, which must detect pulsatile Doppler signals. Even in the best of hands, how-
be distinguished from one another.The basic distinction between ever, this technique remains unreliable in predicting subsequent
arterial and venous pathologic conditions is relatively simple. In bowel viability.
mesenteric ischemia resulting from venous disease, the bowel typ- Other diagnostic options include I.V. administration of fluores-
ically is diffusely edematous, congested, and dilated. In mesen- cein, transcutaneous oxygen measurement, and second-look ex-
teric ischemia resulting from arterial disease, the small bowel is ploratory laparotomy. All of these measures are relatively simple
typically contracted during the early phase of presentation, to perform, but each has its limitations.


Discussion
Mesenteric Ischemia and Reperfusion Outcome after Surgical Treatment
Although acute mesenteric ischemia is initially managed surgi- Most studies that include a large number of patients with acute
cally, significant morbidity and mortality remain after treatment, mesenteric ischemia report perioperative mortalities ranging from
largely resulting from local and systemic inflammation and the 32% to 69% and 5-year survival rates ranging from 18% to
subsequent development of multiple organ dysfunction syndrome 50%.1,27,28 One group performed a systematic review of survival
(MODS). Mesenteric ischemia-reperfusion promotes local syn- after acute mesenteric ischemia according to underlying cause by
thesis and release of various inflammatory mediators that exacer- evaluating available data from the period between 1966 and
bate gut injury and prime circulating neutrophils for enhanced 2002.29 The investigators examined a total of 45 observational
superoxide anion production and subsequent remote (i.e., pul- studies, which included 3,692 patients with acute mesenteric
monary and hepatic) injury.11 At the cellular level, mesenteric ischemia. They reported that mortality varied substantially
ischemia-reperfusion activates a cascade of oxidative stress-sensi- according to the cause of the acute mesenteric episode. Overall
tive protein kinases that converge on specific transcriptional fac- mortality was lower with ischemia of venous origin (i.e., MVT)
tors to regulate expression of proinflammatory genes.These gene than with ischemia of arterial origin.Within the category of arter-
products include enzymes (e.g., inducible nitric oxide synthase ial causes, mortality was 54.1% after treatment of arterial embol-
[iNOS], cyclooxygenase, and phospholipase A2), cytokines (e.g., ic disease, 77.4% after treatment of arterial thrombotic disease,
tumor necrosis factor–α [TNF-α] and interleukin-1 [IL-1]), and 72.7% after treatment of NOMI. The difference in mortality
chemokines (e.g., IL-8), and adhesion molecules (e.g., intercellu- between embolic and thrombotic disease may be accounted for by
lar adhesion molecule–1 [ICAM-1]).12-18 Excessive gene activa- the tendency of thrombosis to occur more proximally and thus to
tion leads to a maladaptive systemic inflammatory response syn- be associated with a greater degree of bowel infarction than
drome that can trigger early MODS. Alternatively, this hyperin- embolic disease is.
flammatory state can cause local gut dysfunction, characterized A 2003 study reviewed the institutional experience at Wake
by histologic evidence of mucosal injury, increased intestinal Forest University between 1990 and 2000.27 A total of 76
epithelial and microvascular permeability, and impaired motility; patients were treated for acute mesenteric ischemia, of whom
patients become more susceptible to bacteremia and endotox- 42% had embolic disease and 58% had thrombotic disease.
emia and, eventually, to late MODS.19 Various surgical treatment options were employed, including
Experimental work suggests that mesenteric ischemia-reperfu- exploration alone, bowel resection alone, and revascularization
sion triggers protein phosphorylation cascades that converge on with or without bowel resection. Overall perioperative mortal-
specific transcription factors to regulate the pattern, timing, and ity was 62%. When mortality was examined in relation to the
magnitude of expression of not only proinflammatory but also cause of ischemia, however, patients with embolic disease
anti-inflammatory gene products.19 Presumably, this process is tended to fare better: overall perioperative mortality was 62%
mediated by alterations in the cellular redox state induced by the to 70% for patients with thrombotic disease and 50% for those
conversion of xanthine dehydrogenase to xanthine oxidase during with embolic disease. None of the patients who underwent
ischemia, with subsequent production of reactive oxygen metabo- exploration alone survived; 33% of those who underwent
lites and H2O2 during reperfusion.20 Alterations in the cellular intestinal resection alone survived. In contrast to perioperative
redox state activate families of stress-sensitive protein kinases, mortality, morbidity was higher in the embolic disease group
such as the nonreceptor tyrosine kinases c-Src and Syk, PI3- than in the thrombotic disease group (69% versus 46%). The
kinase/Akt, and the mitogen-activated protein kinases.These par- 5-year survival rates were dismal in both groups (18%).
allel kinase cascades phosphorylate nascent transcription factors Peritonitis and bowel necrosis at presentation were found to be
(e.g., nuclear factor–κB [NF-κB] and AP-1), which target genes independent predictors of death or survival dependent on total
that encode proteins involved in mediator synthesis.19,21 parenteral nutrition.
Therapies directed at attenuating these pathways have been suc- In a 10-year institutional review from the Mayo Clinic,1 a total
cessful in laboratory models of mesenteric ischemia-reperfusion of 58 patients were treated for acute mesenteric ischemia. Overall
and may eventually be able to affect outcome in patients present- 30-day mortality was 32%; however, when the data were further
ing with acute intestinal ischemia.22-26 However, clinical trials inves- analyzed according to the cause of ischemia, it was found that
tigating the efficacy of pharmacologic blockade of individual medi- mortality from embolic disease was 31%, mortality from throm-
ators (e.g., TNF-α, IL-1, and iNOS) have found this approach to botic disease was 32%, and mortality from NOMI was 80%.
be largely unsuccessful and sometimes even deleterious in treating Multiple organ failure was the most frequent cause of death.The
patients with sepsis and MODS.22 The reasons for the failure of 1-year and 3-year cumulative survival rates were 43% and 32%,
these trials are probably multifactorial, but it appears that both the respectively. Independent predictors of survival included age less
redundancy and breadth of the inflammatory cascade and the poor than 60 years, bowel resection, and the absence of a recent major
timing of therapy (i.e., the inability to target early inflammatory cardiovascular procedure.
events) are major contributing factors. Nonetheless, it is likely that From these studies, it is apparent that acute mesenteric
to achieve any meaningful improvements in our ability to treat ischemia is a lethal disease that carries a high morbidity and
patients with acute mesenteric ischemia, we will have to expand mortality. The only way to reduce the morbidity and mortali-
our knowledge of the early molecular pathways involved in the acti- ty associated with this disease process is to diagnose and treat
vation and proliferation of both local and systemic inflammation. it early, before irreversible signs of bowel ischemia develop.


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