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232 A. Chaus et al.
injury. Intravenous fluid resuscitation with crystalloids should be started prom ptly
to maintain intravascular volume and correct volume deficits. If there is no contraindication to anticoagulation, such as an active bleed as in ischemic colitis,
therapeutic IV heparin should be administered to limit thrombus propagation.
Broad-spectrum antibiotics should be started with focus on covering anaerobes and
gram-negative organisms. Common antibiotics include cefepime with metronidazole, pipercillin-tazobactam, or meropenem. If vasopressors are required, vasoconstricting agents should be avoided to prevent exacerbation of mesenteric
ischemia. Vasopressors such as dobutamine, low-dose dopamine, or milrinone
should be considered to decrease the effect on mesenteric perfusion compared to
other vasopressors.
The goal of treatment is to rapidly restore intestinal blood flow. The specific
approach to treatment depends on whether the occlusion is embolic or thrombotic
(Fig. 25.5a, b). Other important clinical factors to take into account include
patient’s risk factors for intervention and clinical stability. Options for treatment
include surgical, endovascular, or a combined approach.
For patients who are poor surgical candidates with extensive infarction and no
meaningful recovery, a palliative approach may be appropriate.
In patients that are hemodynamically stable with no signs of advanced ischemia,
it may be appropriate to observe on anticoagulation if good collateral circulation is
seen on imaging. Frequent lab studies and serial physical exams should be performed with low threshold for repeat imaging or intervention if symptoms progress.
Patients that are good surgical candidates with signs of advanced ischemia such
as peritonitis, free air, or pneumatosis, should be immediately taken for laparotomy.
While undergoing surgical exploration, bowel viability should be assessed. If the
bowel is viable, attempts at reperfusion with methods such as thromboendarterectomy, mesenteric bypass, mesenteric stent should precede bowel resection.
For an embolic source for mesenteric occlusion, open surgical embolectomy is
traditionally performed with removal of the thrombus, direct visualization and
assessment for bowel viability. In mesenteric thrombosis, mesenteric bypass may be
the preferred option because a thrombectomy may not provide a long-term solution
for advanced atherosclerosis. Other surgical options for mesenteric thrombosis
include retrograde angioplasty and arterial stenting. For hemodynamically stable
patients with no signs of advanced ischemia, an endovascular approach may be
appropriate. For patients with acute embolism, options include percutaneous clot
aspiration or catheter-directed thrombolytic therapy. In patients with acute thrombosis, angioplasty/stenting is another reasonable option (see next section).
Surgical
Laparotomy—For patients with findings consistent with peritonitis, a laparotomy is
indicated to evaluate the extent of intestinal infarction. During the laparotomy,
appearance, pulsations, bleeding from cut surfaces, peristalsis is evaluated. The
intestinal tract is also assessed for impending or gross perforation. If bowel
25 Mesenteric Arterial Occlusion 233
Fig. 25.5 Algorithms for management of acute embolic (a) and thrombotic mesenteric arterial
(b) occlusion. Reproduced with permission from: Morgan J, Raut CP, Duensing A, Keedy VL.
Epidemiology, classification, clinical presentation, prognostic features, and diagnostic work-up of
gastrointestinal stromal tumors (GIST). In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA.
(Accessed on [Date].) Copyright © 2020 UpToDate, Inc. For more information visit www.
uptodate.com
234 A. Chaus et al.
Fig. 25.5 (continued)
25 Mesenteric Arterial Occlusion 235
perforation is evident, the segment that is affected is resected with reconstruction or
stoma formation until a second look laparotomy. Arterial revascularization is preferred and should precede bowel-resection in almost all patients, except when a
segment of bowel is clearly non-viable. If there is question of bowel viability,
perfusion should be restored and bowel viability should then be reassessed. For a
majority of patients, a second-look laparotomy after mesenteric revascularization is
performed, usually 24–48 hours after the initial laparotomy.
Surgical Revascularization
Open SMA Embolectomy—Arterial revascularization is preferred over resection.
When a laparotomy is performed, the SMA is exposed. A transverse arteriotomy is
then performed, a 3 or 4 Fr Fogarty catheter is introduced to embolectomy catheters
are then introduced to remove the clot. Restoration of pulsatile blood flow confirms
clearance of the thrombus after multiple passes are made and there is confirmation
of absence of additional thrombi. Confirmation can be done by angiography of the
SMA or transit time flow measurement. If neither are available, palpation of the
pulse distally in the mesentery can be performed.
SMA Bypass—Typically used in patients with arterial thrombosis due to
atherosclerotic disease. This is usually a vascular bypass graft that can originate
from the infrarenal or supraceliac aorta. Autologous reversed saphenous vein is the
preferred conduit to avoid intra-abdominal contamination from perforation or
infarction of the bowel. Pre-operative CTA can be used to guide decision-making
and can be used to determine sites with extensive atherosclerotic lesions. Bypass
from the infrarenal aorta to the SMA is the simplest procedure that can be performed; however, the aorta is often heavily calcified and is therefore rarely performed. The supraceliac aorta or the anterior common iliac artery may be used as
the inflow vessel.
Endovascular Procedures
An endovascular approach is considered in patients who are hemodynamically
stable with no signs of advanced ischemia. Options include aspiration embolectomy, balloon angioplasty with stent placement, local pharmacologic thrombolysis.
Aspiration embolectomy—A catheter is passed into the ileocolic branch of the
SMA. An introducer is placed proximal to the embolus in the SMA with aspiration
with a smaller guiding catheter. Angiography is then performed and repeated
aspirations done to remove clots (Fig. 25.6).
Angioplasty with stenting—Stenting can be performed in an anterograde vs
retrograde fashion. In the antegrade approach, the catheter is introduced through the
aorta into the SMA. A balloon expandable stent is placed at the level of the stenosis.
Results are conformed by angiography and pressure measurements. A pressure
gradient of more that 12 mmHg would indicate the need for additional angioplasty
and/or stenting.
236 A. Chaus et al.
Fig. 25.6 Aspiration
embolectoy of the SMA
Transverse
incision
Embolus
If percutaneous access fails, laparotomy is performed with exposure of the SMA.
A retrograde approach with recanalization and stenting is an option for reperfusion.
The retrograde approach is performed with the device introduced distal to the
obstruction via the SMA. Periodic stent surveillance should be done using duplex
ultrasound or CT angiography, however, there are no specific guidelines for
post-intervention follow-up.
Local SMA thrombolysis—In patients with incomplete aspiration embolectomy
or distal mesenteric embolization, catheter-directed thrombolysis is an alternative.
Low-dose heparin (500 units/hour) is administered after an end-hole catheter is
advanced up to the clot or a multiple sidehole catheter is advanced through the clot.
Infusion should be stopped if progressive signs of ischemia occur. Arteriography is
repeated within the first four hours to assess for clot lysis. If this is not accomplished, abdominal exploration in the OR is indicated.
25 Mesenteric Arterial Occlusion 237
Medical Therapy
Medical treatment for those who survive after acute mesenteric arterial occlusion is
focused on improving long-term survival. For patients with an embolic source for
the occlusion, treatment should focus on the prevention of future embolic events.
For atrial fibrillation, therapy with novel oral anticoagulants or a vitamin k
antagonist is indicated. For patients with mesenteric arterial occlusion due to
atherosclerosis, antiplatelet therapy and stain is indicated, in addition to decreasing
risk factors such as tobacco use. A meta-anal ysis that studied the efficacy and safety
of intensive lowering of LDL cholesterol, looked at 170,000 participants in 26
randomized trials. This meta-analysis concluded that there a 10% reduction in total
mortality per 1.0 mmol/L reduction in LDL levels.
Prognosis
Mortality from acute mesenteric occlusion is high, even with aggressive treatment
approaches. In patients undergoing intervention for acute mesenteric arterial
occlusion, with open and endovascular treatment, perioperative mortality was 22%
with complications occurring in 68%. Additionally, mortality was similar for open
and endovascular approaches. Causes of death included, but not limited to,
intra-abdominal sepsis with multiorgan dysfunction, hemorrhage, and cardiac
causes. Complications for those who survived bowel resection develop short-gut
syndrome, requiring long-term parenteral nutrition.
Suggested Reading
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Ischemic Enteropathy (Also Called Mesenteric Ischemia)
Dorsa Samsami and Eli D. Ehrenpreis
Definition and Description of the Disease
Diminished small intestinal blood flow and its associated consequence are termed
either ischemic enteropathy or small intestinal mesenteric ischemia. This condition
can arise from a decrease in arterial or venous supply to the small intestine.
Classification and Terminology
There are a variety of classifications systems used to characterize decreased blood
flow of mesenteric vascular origin. For the purpose of this chapter, mesenteric
ischemia is divided by temporal occurrence (acute versus chronic) and the site of
diminished mesenteric blood flow (arterial versus venous). A variety of etiologies
of acute and chronic mesenteric ischemia are presen t. According to most classification systems, mesenteric ischemia affecting the colon alone is termed ischemic
colitis (Table 26.1). Because of contrasting etiologies, presentations and treatments
for ischemic colitis, this chapter will focus on small intestinal disease caused by
diminished mesenteric blood flow. Furthe r details regarding colonic disease are
presented in Chap. 27 Ischemic Colitis.
Acute mesenteric ischemia is characterized by the sudden disruption of blood
flow in the mesenteric vasculature and is associated with devastating clinical
consequences. Chronic mesenteric ischemia is characterized by a more insidious
26
D. Samsami
Department of Internal Medicine, Advocate Lutheran General Hospital,
1775 Dempster St, 6 South, Park Ridge, IL 60068, USA
E. D. Ehrenpreis (&)
Department of Medicine, Advocate Lutheran General Hospital,
1775 Dempster St, 6 South, Park Ridge, IL 60068, USA
e-mail: e2bioconsultants@gmail.com
© Springer Nature Switzerland AG 2021
E. D. Ehrenpreis et al. (eds.), The Mesenteric Organ in Health and Disease,
https://doi.org/10.1007/978-3-030-71963-0_26
239
240 D. Samsami and E. D. Ehrenpreis
Table 26.1 American
gastroenterological
association classification of
mesenteric ischemia
Acute mesenteric ischemia
Superior mesenteric artery thrombosis
Superior mesenteric artery embolus
Nonocclusive mesenteric ischemia
Superior mesenteric vein thrombosis
Focal segmental ischemia
process due to the slow development of mesenteric arterial obstruction and the
abundance of collateral blood flow to the intestines. Late complications of
mesenteric ischemia include intestinal stricture and short bowel syndrome.
Acute ischemic enteropathy is a serious medical condition that may lead to
bowel infarction and sepsis with an overall morbidity and mortality approaching
50%. Because of its severity and potential for rapid and fatal consequences, early
diagnosis of ischemic enteropathy is of vital importance. Acute intestinal ischemia
may be result of either arterial or venous obstruction, while chronic mesenteric
ischemia is primarily due to atherosclerotic narrowing of and diminished blood flow
through the mesenteric arterial circulation.
Intestinal Vascular Anatomy
The arterial supply to the intestines is primarily from the superior mesenteric artery
and the inferior mesenteric artery. The superior mesenteric artery supplies the entire
small intestine except for the proximal duodenum. Both the superior and inferior
mesenteric arteries supply the colon. There is also an ex tensive collateral circulation
to the intestines. (See Chap. 4, Mesenteric Vascular Anatomy).
Epidemiology
Acute mesenteric ischemia is estimated to be the primary diagnosis for 0.1% of
hospital admissions. Mesenteric arterial occlusion is the cause in 1% of patients
presenting with an acute abdomen. Mesenteric artery stenosis occurs in as many as
10% of the population over 65 years of age. The majority of these patients are
asymptomatic, with chronic mesenteric ischemia accounting for about 5% of
intestinal ischemic events. The disparity between the occurrence of mesenteric
artery stenosis and the development of chronic mesenteric ischemia is due in part to
the extensive network of arterial collaterals. This network provides compensation
for diminished blood flow from stenotic mesenteric arteries.
26 Ischemic Enteropathy (Also Called Mesenteric Ischemia) 241
Patients at Risk
Risk factors for acute mesenteric arterial occlusion include any processes that are
associated with diminished mesenteric blood flow, intrinsic arterial or venous
thrombosis or increase the potential for mesenteric arterial embolism. These include
congestive heart failure, cardiac arrhythmia, valvular heart disease, infective
endocarditis, aortic atheroscle rosis, acute myocardial infarction, aortic aneurysm,
and ventricular aneurysm. Patients with peripheral arterial disease, advanced age,
and low cardiac output are at increased risk of acute mesenteric ischemia. Other risk
factors include the use of vasoconstrictive medications and drugs of abuse, primary
and secondary causes of increased platelet concentration, and vasculitis, most
commonly polyarteritis nodosa.
Chronic mesenteric ischemia occurs in patients with mesenteric arterial
atherosclerosis. Risk factors for chronic intestinal ischemia include hyperlipidemia,
hypertension, smoking and diabetes mellitis. Symptoms present most commonly
between the ages of 50 and 70 in patients with pre-existing atherosclerotic disease.
Chronic mesenteric ischemia is more common in females. Specific etiologies of
acute mesenteric ischemia and their frequency of occurrence are shown in in
Table 26.2.
Pathophysiology
Between 25 and 35% of cardiac output is directed toward splanchnic blood flow,
the majority of which supplies the mucosal and submucosal layers of the intestine.
Multiple regulatory pathways are involved in the maintenance of adequate blood
flow to the intestines. These pathways may be viewed as having intrinsic components involving local metabolic and myogenic functions and extrinsic components
involving neural and humoral regulatory systems, Decreased splanchnic blood flow
resulting from arterial or venous obstruction or dysregulation related to the aforementioned pathways, all may result in the development of ischemic damage to the
intestine.
Table 26.2 Causes and approximate frequencies of acute mesenteric ischemia
Etiology Cause Frequency (%)
Arterial Superior mesenteric artery thrombosis 54–68
Superior mesenteric artery embolus 26–32
Nonocclusive mesenteric ischemia 10
Venous Superior mesenteric vein thrombosis 5
Focal segmental ischemia 5
Adapted from Brandt LJ, Feuerstadt P. Intestinal Ischemia. In: Gastrointestinal and Liver Disease.
10th ed. p. 2076–2101