Mesenteric ischemia

Mesenteric IschemiaCHAIRMAN – DR. ANIL P BELLAD

CO CHAIRMAN – DR. BINITA MALLAPUR

PRESENTER – DR S S K KANTH KAVIPURAPU

Introduction Mesenteric ischemia is a frequently lethal condition resulting from critically reduced

perfusion to the gastrointestinal tract.

Acute and chronic forms

Involves Arterial and venous sides of circulation

First described in 1500s

Despite remarkable advances in vascular surgical technique, vascular imaging, percutaneous intervention, and surgical critical care, mesenteric ischemia remains a complex and often disheartening disease.

Statistics 0.1 % of hospital admissions

1%-2% of admissions for abdominal pain

Incidence – 9 in 100,000 person – years

Incidence increases with age

More common in women

Mortality – 24% to 96% with average of 69%

Mesenteric vasculature

Comprises of 3 major aortic branches with collaterals Celiac axis

Superior mesenteric artery

Inferior mesenteric artery

Celiac axis – foregut (distal esophagus to duodenum, hepatobiliary, spleen) Left gastric artery

Splenic artery

Common hepatic artery

Mesenteric vasculature Superior mesenteric artery – midgut ( Jejunum to mid colon )

Inferior pancreaticoduodenal artery

Jejunal branches

Ileal branches

Middle colic artery

Right colic artery

Ileocolic artery

Inferior mesenteric artery – hindgut ( mid colon to rectum ) Left colic artery

Sigmoid arteries

Superior rectal artery

Types

Acute mesenteric ischemia

Chronic mesenteric ischemia

Non occlusive mesenteric ischemia


Acute mesenteric ischemia (AMI) may be defined as an abrupt reduction in blood flow to the intestinal circulation of sufficient magnitude to compromise the metabolic requirements and potentially threaten the viability of the affected organs

Emboli (50%)

Arrhythmia

Valvular disease

Myocardial infarction

Hypokinetic ventricular wall

Cardiac aneurysm

Aortic atherosclerotic disease

Iatrogenic

Thrombosis (25%)

Atherosclerotic disease

Nonocclusive (5% to 15%)

Pancreatitis

Heart failure

Sepsis

Cardiac bypass

Burns

Renal failure

Medications


Paradoxical embolus traveling through a patent foramen ovale from a thrombus in the venous system

Venous occlusion Hypercoagulable state

Sepsis

Compression

Pregnancy

Portal hypertension

Malignancy

Embolic occlusion

Emboli lodge commonly in Superior Mesenteric artery.

>50% - mid to distal segment

The SMA tapers after major branch points

Emboli commonly found distal to the middle colic artery

<15% of emboli occlude the SMA at its origin

Embolic occlusion

Point of occlusion affects the magnitude and distribution of the ischemia

Occlusion at the origin - ligament of Treitz to the transverse colon

Occlusion distal to the middle colic artery - Preserves the right colon and proximal part of the small bowel

Thrombotic occlusion 25% - 30% of acute mesenteric ischemia

Conjunction with chronically diseased arteries

No symptoms/ minimal symptoms until the occlusive event

May be due to rupture of a previously noncritical atherosclerotic plaque that abruptly occludes the vessel.

Non Occlusive mesenteric ischemia

20% of all cases of acute mesenteric ischemia

Occurs with patent mesenteric arteries

Splanchnic vasoconstriction - pathophysiologic process Precipitated by hypoperfusion from medications, depressed cardiac output, or

renal or hepatic disease

Blood pressure in the bowel falls below a critical pressure of 40 mm Hg, ischemia develops and eventually leads to infarction and bowel necrosis.

Pathophysiology Intestinal blood flow accounts for 10 to 20% of the resting cardiac output but may,

on occasion, exceed 30%.

Regulated by a variety of mechanisms, including The autonomic nervous system,

Neurohormonal factors

Gastrin,

Glucagon

Secretin

Bradykinin, serotonin, histamine, and the prostaglandins.

Of the blood reaching the intestinal wall, most is directed toward the mucosa, the layer with the greatest metabolic demand and highest rate of cell turnover.

Pathophysiology

Sudden reduction of the blood supply to the viscera changes associated with organ ischemia

Specifically compromises the mucosal barrier function.

Changes follow with an inflammatory cell infiltrate

Bowel wall edema ensues as a result of loss of capillary integrity

Pathophysiology

Absence of this natural barrier bacterial translocation,

promotion of endotoxemia,

exudation of fluid into the bowel lumen.

Injured mucosa sloughs, leaving ulcerations of the bowel wall.

The bowel may still be viable when the mucosa is threatened

Prolonged interruption of blood flow Necrosis of the muscularis and serosa

Compromised segment is no longer salvageable.

Pathophysiology

Interruption of mesenteric blood flow initiates tissue injury and systemic illness,

Deleterious effects catalyzed by oxygen free radicals and other toxins. Myocardial depression,

Progressive inflammatory response

Generalized increase in capillary permeability,

Edema and organ dysfunction.

Diagnosis Classical - Abdominal pain out of proportion to the findings on physical

examination and persisting beyond 2 to 3 hours

Diarrhoea

Nausea

Vomiting

Anorexia

Abdominal distention

Melena / hematochezia / occult fecal blood – 15%

Full thickness bowel involvement

Acute abdomen

Distention, guarding, rigidity, hypotension – peritonitis – septic consequences

Diagnosis Complete hemogram

Hemoconcentration – dehydration and hypovolemia

Leucocytosis

Evaluation of renal and hepatic function,

Blood urea nitrogen, Creatinine,

amylase, lipase,

prothrombin time, activated partial thromboplastin time

cardiac enzymes

Diagnosis

Metabolic acidosis

Hyperamylasemia

Elevation of lactate dehydrogenase, aspartate aminotransferase, and creatine phosphokinase.

Hyperkalemia and hyperphosphatemia are present - Bowel infarction

ECG - cardiac rhythm.

Diagnosis

Plain x rays - Non diagnostic

Ultrasonography – Limited utility in acute mesenteric ischemia

CT scan

Magnetic resonance angiography – Not a choice in acute state

Arteriography – Method of definitive diagnosis

Plain x-ray Supine / erect

Chest – AP view

Suspicious findings Non specific ileus

Dilated bowel loops

Thumb printing

Separation of bowel loops

Intramural gas

Free air

Majority of the cases plain films are non diagnostic

CT scan Indirect findings of arterial bowel ischemia and may show the arterial occlusion or mesenteric venous

thrombus.

Dilation of the bowel lumen,

Bowel wall thickening

Abnormal bowel wall enhancement,

Arterial occlusion,

Venous thrombosis

Intramural or portal venous gas

CT scan

Symmetrical bowel wall thickening greater than 3 mm in a distended segment of bowel suggests ischemia

Greater degrees of bowel wall thickening should raise suspicion of mesenteric venous thrombosis (MVT).

Intravenous contrast is useful in demonstrating the heterogeneity of the ischemic bowel wall (lack of bowel wall enhancement) and may show occlusion of mesenteric arteries if given by rapid bolus administration

CT scan

Pathologic Damage CT Findings

Vasoconstriction Wall hyper density

Absence of wall enhancement

Increased capillary permeability Wall thickening

Bowel dilation

Mucosal cellular necrosis Pneumatosis

Gas in mesenteric vein branches

Gas in portal vein branches

Transmural bowel necrosis Pneumoperitoneum

Retropneumoperitoneum

Ascites

CT scan Sensitivity - 64%

Specificity - 92%

CT is the diagnostic technique of choice for acute MVT sensitivity exceeding 90%.

3D recon of the aorta and its branches show additional detail sensitivity and specificity to 94% to 96%

The limitations and risks of CT angiography renal insufficiency or contrast allergies

limitations of contrast volume, and metal artefacts obscuring the area of interest

Arteriography Definitive diagnosis - acute and chronic mesenteric ischemia.

Arteriograms Establish the diagnosis

Assist in differentiating between acute embolic, thrombotic, or nonocclusive mesenteric ischemia

Allow proper planning of the revascularization procedure.

AP and lateral views of the aorta and the mesenteric branches are required for proper arteriographic evaluation.

The lateral view is particularly important to examine the proximal celiac artery and SMA, which overlap the aortic contrast column on AP views.

Arteriography

Acute embolic occlusion of the SMA is abrupt occlusion of the artery, usually at a branch point where the vessel tends to narrow

If imaged acutely, a meniscus sign (crescent) is often observed.

If secondary thrombosis occurs proximal to the embolus, the classic meniscus sign of embolic occlusion will be obscured.

Management

Effective management Early diagnosis

Aggressive resuscitation

Early revascularization

On going supportive care

Medical treatment

Surgical treatment

Endovascular Treatment

Treatment Fluid resuscitation

Systemic anticoagulation - Heparin

Significant metabolic acidosis not responding to fluid resuscitation should be corrected with sodium bicarbonate.

A central venous catheter, peripheral arterial catheter, and a Foley catheter should be placed for hemodynamic status monitoring.

Appropriate antibiotics are given before surgical exploration.

Primary goal of surgical treatment in embolic mesenteric ischemia is to restore arterial perfusion with removal of the embolus from the vessel

Surgical treatment Operative intervention remains the mainstay of management

The surgeon's goal is to confirm the diagnosis

Assess bowel viability,

Determine the responsible etiology,

Perform revascularization where possible

Resect nonviable bowel

Surgical treatment

The abdomen is explored - midline incision - reveals variable degrees of intestinal ischemia from the mid jejunum to the ascending or transverse colon.

The SMA is approached at the root of the small bowel mesentery.

Once the proximal SMA is identified and controlled with vascular clamps, a transverse arteriotomy is made to extract the embolus, using standard balloon embolectomy catheters.

Surgical treatment

Following the restoration of SMA flow,

Assessment of intestinal viability must be made,

Nonviable bowel must be resected.

Several methods Intraoperative IV fluorescein injection and inspection with a Wood's lamp

Doppler assessment of antimesenteric intestinal arterial pulsations.

A second-look procedure - 24 to 48 hours following embolectomy.

The goal of the procedure is reassessment of the extent of bowel viability, which may not be obvious immediately following the initial embolectomy.

Surgical treatment

Thrombotic mesenteric ischemia - severely atherosclerotic vessel

Typically the proximal CA and SMA.

Require a reconstructive procedure to the SMA to bypass the proximal occlusive lesion and restore adequate mesenteric flow.

The saphenous vein is the graft material of choice

Prosthetic materials should be avoided in patients with nonviable bowel, due to the risk of bacterial contamination if resection of necrotic intestine is performed.

Suspected Acute mesenteric ischemia

Mesenteric arteriogram

Normal arteriogramR/O

mesenteric venous

thrombosis

Peritoneal signs

No

observe

Yes

Exploratory laparotomy

Non-occlusive mesenteric ischemia

(vasoconstriction)Anticoagulation

SMA catheter with papaverine

infusion

Peritoneal signs

Yes

Exploratory laparotomy

Continue papaverine

Repeat arteriogram Clinical

evaluation

Second look laparotomy

No Continue papaverine Clinical

evaluationRepeat

arteriogram

Small branch occlusion/embolus

Anticoagulation

Vasoconstriction

Yes

No Peritoneal signs

Yes Exploratory laparotomy

No Continue anticoagulation

observe

Aggressive resuscitation Swan ganz catheter, volume repletion/blood, antibiotics

Endovascular treatment

Catheter-directed thrombolytic therapy is a potentially useful treatment modality

Initiated with intra-arterial delivery of thrombolytic agent into the mesenteric thrombus at the time of diagnostic angiography.

Various thrombolytic medications, including urokinase or recombinant tissue plasminogen activator have been reported to be successful

Catheter-directed thrombolytic therapy has a higher probability of restoring mesenteric blood flow success when performed within 12 hours of symptom onset.


Successful resolution of a mesenteric thrombus - facilitate the identification of the underlying mesenteric occlusive disease process.

Subsequent operative mesenteric revascularization or mesenteric balloon angioplasty and stenting may be performed electively

Main drawbacks Percutaneous, catheter-directed thrombolysis (CDT) does not allow the possibility

to inspect the potentially ischemic intestine following restoration of the mesenteric flow.

Prolonged period of time - achieve successful CDT,

An incomplete or unsuccessful thrombolysis

Acute Mesenteric venous thrombosis

MVT - 5% to 15% of patients

The superior mesenteric vein is most commonly

frequently with extension of thrombus into the portal vein.

The inferior mesenteric vein is most often spared.

Clinical findings – extent of thrombosis,

the mesenteric veins involved

degree of bowel wall ischemia.

Mortality rate - up to 50%

Clinical features

Midabdominal colicky pain

Diffuse and nondescript nature of their symptoms - delay

Nausea,

vomiting,

Diarrhea, and anorexia

Occult blood in the stool are present in half of the patients,

Hematemesis, hematochezia, or melena - 15%.

Past medical history or family history - informative because venous thromboembolism

Physical findings - early arterial mesenteric ischemia.

Abdomen soft,

Early stage – No tenderness/ peritoneal signs

Advanced disease - Fever, muscular guarding, rebound tenderness

Bowel infarction ultimately develops in 30% to 60% of patients with acute MVT.

Fluid sequestration within the bowel wall and lumen and the development of ascites, hypotension with hemodynamic instability is often part of the clinical picture. Patients first seen in this advanced clinical condition have a poor prognosis.

Blood tests are obtained but are not generally helpful. Elevation of the white blood count with a shift toward immature white cells can be found in 50% to 65% of patients.[51] Serum amylase is usually normal, and serum lactate is elevated only in patients with advanced bowel ischemia and suggests necrosis.

Plain abdominal films are often the initial diagnostic test and are generally of little value. Although abnormalities can be found in 50% of patients,[47] the findings are nonspecific. Thumbprinting, when seen, is indicative of the mucosal edema resulting from venous congestion. Pneumatosis intestinalis, portal vein gas, and free air in the abdomen usually represent bowel infarction.[52]

CT of the abdomen with intravenous contrast is the diagnostic test of choice for patients with suspected acute MVT. A definitive diagnosis can be made in more than 90% of patients. Harward et al.[50] reported 90% sensitivity of abdominal CT with observation of a luminal venous thrombus. However, if one includes other characteristic findings of the bowel wall, such as thickening, pneumatosis, or streaking of the mesentery, CT sensitivity increases to nearly 100%.[33,52] Magnetic resonance venography is used less commonly, but when properly performed, it is highly sensitive.

Depending on the timing of the examination, color duplex ultrasound of the mesenteric veins can be helpful. If performed early, before significant bowel distention, a sensitivity of 80% or greater can be anticipated.[53]

Selective mesenteric arteriography is not frequently used to establish the diagnosis of MVT, although it may be helpful in the management of these patients. Findings such as incomplete filling of the mesenteric veins, prolonged opacification of the arterial arcades, and the presence of thrombus or nonfilling of the superior mesenteric, splenic, or portal vein (Fig. 84-5) are seen in these patients. Most report a sensitivity of 70% to 80%.[54,55]

Treatment is generally directed at limiting progressive venous thrombosis, reducing the risk for bowel necrosis, and performing timely resection in those with irreversible bowel ischemia. Unfortunately, because of delay in diagnosis, the diffuse nature of the thrombosis, and the rarity of this condition, treatment directed at restoring patency to the thrombosed veins is unusual. In light of the rapid technologic advances in percutaneous interventions, which incorporate pharmacologic and mechanical methods of thrombus dissolution/extraction, it appears reasonable, if not advisable to initiate a strategy of thrombus dissolution/extraction to restore venous drainage because with the traditional care of anticoagulation alone, these patients continue to face a mortality rate ranging from 15% to 50%.[48,50,55,56] The diagnosis of MVT should trigger a search for an underlying thrombophilia. Such an evaluation includes factor V Leiden, prothrombin gene mutation, antiphospholipid/anticardiolipin antibodies, antithrombin III, protein C, protein S, factor VIII levels, hyperhomocysteinemia, paroxysmal nocturnal hemoglobinuria, and assessment for an underlying myeloproliferative disorder.

Rapid initiation of systemic anticoagulation is important. In patients with localized or diffuse peritoneal irritation, exploratory laparotomy is indicated. Laparoscopy should be avoided in these patients because the increased abdominal pressure associated with the pneumoperitoneum further diminishes mesenteric blood flow.

On entering the abdomen, the superior mesenteric and portal veins should be assessed to determine the relative age of the thrombus. If the large veins appear to have an acute thrombus within them, thrombectomy is recommended, followed by bolus infusion of a recombinant tissue plasminogen activator (rt-PA) solution. The authors use a high-volume, low-dose solution of rt-PA, typically diluting 2 mg in 50 ml and infusing the entire 2-mg dose. Necrotic bowel is conservatively resected with preservation of viable intestine. The patient is treated with heparin intraoperatively and anticoagulation is continued postoperatively.

Associated arterial vasospasm should be evaluated by arteriography and treated with catheter-directed papaverine into the SMA, which improves perfusion to the ischemic bowel and reduces the necessity for additional resection. Patients treated for MVT have a high risk of recurrence (35% to 70%),[49] most frequently within 30 days, thus emphasizing the need for early and persistent anticoagulation.

Patients surviving the acute episode of MVT face chronic mesenteric venous hypertension with a subsequent risk for varices. This post-thrombotic venous hypertension occurs most commonly in patients with persistent large-vein mesenteric thrombosis, which further supports a strategy to remove the thrombus in patients with acute large-vein MVT. Some have reported success with transhepatic portography and instillation of a plasminogen activator directly into the thrombus.[57,58] Unfortunately, thrombolytic agents have been used infrequently in these patients because of the perceived risk for hemorrhage. The success of thrombolysis is often compromised by the delay in diagnosis. Intrathrombus thrombolytic therapy and, alternatively, intra-arterial thrombolytic therapy via the SMA should be considered in patients with thrombosis of large mesenteric veins when the potential benefit outweighs the risk of bleeding.

Chronic Mesenteric ischemia Commonly the result of advanced atherosclerotic disease of multiple mesenteric

arteries.

Good collateral circulatory - symptomatic chronic mesenteric ischemia is rare.

Risk factors a positive family history,

smoking,

hypertension,

hypercholesterolemia.

More common in females

Chronic Mesenteric ischemia Non atherosclerotic causes - less frequent

inflammatory arterial disease,

middle aortic syndrome,

celiac artery compression (median arcuate ligament syndrome),

chronic aortic dissection, aortic coarctation,

fibromuscular dysplasia,

neurofibromatosis.

Chronic Mesenteric ischemia

Occlusive disease – more common

Obliterative disease of the celiac or mesenteric artery -14% to 24%.

Visceral artery stenosis - frequent,

Symptoms - uncommon (extensive collateral circulation)

As imaging techniques - common - stenosed visceral arteries detected more frequently

Clinical features

Classic picture Postprandial abdominal pain

Weight loss.

Pain - intestinal angina / intestinal claudication Diffuse - Midabdominal, midepigastric, and crampy in nature.

Develops within 15 to 45 minutes after eating,

Severity - size of the meal ingested.

Early-onset pain with foregut (celiac artery distribution) ischemia,

Later-onset pain - diffuse ischemic disease.

Clinical features

Nausea,

Vomiting

Diarrhea

Bloating

Constipation

Occult blood in stool and ischemic colitis - hindgut ischemia.

Diagnosis

Non invasive mesenteric duplex scan Fasted state

Sensitivity – 75%, Specificity – 92%

Aortography

CT angiogram

Magnetic resonance angiography

Treatment

The therapeutic goal in patients with chronic mesenteric ischemia is to revascularize mesenteric circulation and prevent the development of bowel infarction. Mesenteric occlusive disease can be treated successfully by either transaortic endarterectomy or mesenteric artery bypass. Transaortic endarterectomy is indicated for ostial lesions of patent CA and SMA. A left medial rotation is performed, and the aorta and the mesenteric branches are exposed. A lateral aortotomy is performed, encompassing both the CA and SMA orifices. The visceral arteries must be adequately mobilized so that the termination site of endarterectomy can be visualized. Otherwise, an intimal flap may develop, which can lead to early thrombosis or distal embolization.

For occlusive lesions located 1 to 2 cm distal to the mesenteric origin, mesenteric artery bypass should be performed. Multiple mesenteric arteries are typically involved in chronic mesenteric ischemia, and both the CA and SMA should be revascularized whenever possible. In general, bypass grafting may be performed either ante grade from the supraceliac aorta or retrograde from either the infrarenal aorta or iliac artery. Both autogenous saphenous vein grafts and prosthetic grafts have been used with satisfactory and equivalent success. An ante grade bypass also can be performed using a small-calibre bifurcated graft from the supraceliac aorta to both the CA and SMA, which yields an excellent long-term result.76


Endovascular treatment of mesenteric artery stenosis or short segment occlusion by balloon dilatation or stent placement represents a less invasive therapeutic alternative to open surgical intervention, particularly in patients whose medical comorbidities place them in a high operative risk category. Endovascular therapy is also suited to patients with recurrent disease or anastomotic stenosis following previous open mesenteric revascularization. Prophylactic mesenteric revascularization is rarely performed in the asymptomatic patient undergoing an aortic procedure for other indications.79 However, the natural history of untreated chronic mesenteric ischemia may justify revascularization in some minimally symptomatic or asymptomatic patients if the operative risks are acceptable, because the first clinical presentation may be acute intestinal ischemia in as many as 50% of the patients, with a mortality rate that ranges from 15 to 70%.79 This is particularly true when the SMA is involved. Mesenteric angioplasty and stenting is particularly suitable for this patient subgroup given its low morbidity and mortality. Because of the limited experience with stent use in mesenteric vessels, appropriate indications for primary stent placement have not been clearly defined. Guidelines generally include calcified ostial stenoses, high-grade eccentric stenoses, chronic occlusions, and significant residual stenosis greater than 30% or the presence of dissection after angioplasty. Restenosis after PTA is also an indication for stent placement.80

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Mesenteric ischemia