Page 1504 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 109: Mesenteric Ischemia 1043

have suggested that this can be done safely with high diagnostic accuracy. embolectomy is carried out first with a balloon catheter (size 3F or 4F). If
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The mini laparoscopy has been advocated increasingly in the critical pulsatile aortic flow is restored, the vessel is reoccluded, and the surgeon
care setting, where there remains diagnostic doubt in a deteriorating proceeds to distal embolectomy. Mesenteric bypass or open angioplasty
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patient, and some have done this safely at the bedside. The generally and stenting is indicated if there is failure to gain satisfactory inflow,
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poor results of open surgery, even in good hands, have encouraged some inability to pass the catheter proximally, inadequate inflow, or a heavily
surgeons to explore less invasive alternatives using laparoscopic tech- diseased vessel. Distal embolectomy is performed with the balloon
niques. Some practitioners have claimed improved survival and reduced catheter (size 3F) into the major branches, until all thrombus is retrieved
morbidity using this approach, but whether these results in specialized and backbleeding is seen. The arterial closure should maintain an ade-
centers can be extended to other settings is unknown. 48 quate lumen and is best achieved with interrupted monofilament sutures,
■ OPEN SURGERY sometimes requiring a patch angioplasty of vein or infection resistant
synthetic material. Restoration of pulsatile flow should be assessed clini-
Most commonly the definitive assessment and management of acute cally by palpation and visualization of the intestinal arterial perfusion and
mesenteric ischemia requires open surgery. The surgeon should checked intraoperatively with sterile Doppler probe (at the bowel-intestinal
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repeat the abdominal examination once the patient is anesthetized. In margin) or duplex ultrasound. Spasm is common in the distal vessels and
the absence of muscle tone and tenderness, new pathology, such as may be relieved by perivascular infusion of papaverine (30 mg).
an abdominal mass or aortic aneurysm, may be detected. Adequate
exposure generally requires a full midline laparotomy with transperi- HYBRID PROCEDURE: RETROGRADE OPEN
toneal approach. Although retroperitoneal approaches to the aorta and MESENTERIC STENTING (ROMS)
branches are useful in chronic mesenteric revascularization, they do not
allow adequate assessment of intestinal perfusion and viability in the In ROMS approach, the visceral peritoneum is incised horizontally or lon-
acute setting. The initial aim is to confirm the diagnosis and rule out any gitudinally at the base of the transverse mesocolon, the SMA is controlled,
major confounding disease. and a local thrombectomy is performed. A localized endarterectomy of
The acutely ischemic intestine may appear remarkably normal prior to the SMA may be performed if necessary. Placing a patch angioplasty then
infarction and before reperfusion. Changes may be focal, segmental, or facilitates retrograde cannulation of the SMA with a long, flexible sheath
global depending on the etiology of the ischemia. The intestine is inspected directed toward the aorta. The artery can be accessed through the patch
for loss of sheen, discoloration (gray through black), and lack of peristalsis. with a purse string suture to aid in control if required. A working sheath
SMA thrombosis typically occurs at the origin, so the distribution of isch- is placed and angiography performed. A guidewire is used to cross the
emia classically involves the entire small bowel and proximal half of the proximal SMA lesion and the area predilated as required. Then the area is
colon. SMA embolism, on the other hand, may spare the right colic branch stented with a low profile balloon-mounted stent to 6 to 7 mm. Mesenteric
and proximal jejunum branches if it lodges distal to the origin. However, angiography will confirm the state of the distal circulation and pressure
the clot may lodge at the origin, giving a similar pattern to thrombosis. measurement can assess any residual stenosis.
Microemboli typically disperse and lodge distally, creating patchy areas of ROMS during emergent laparotomy for AMI is a promising technique
ischemia with normal intervening segments. Delicate palpation for arte- and an attractive alternative to emergent surgical bypass. This method
rial pulsation must be carried from the root of the SMA to its mesenteric needs to be tested by others to determine its true value in comparison to
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branches. Visible pulsation may be seen in the mesenteric arterial arcades. traditional methods.
may reveal an absence of flow in the main branches, arcades, or the intes- ■ SUPERIOR MESENTERIC ARTERY BYPASS
More objective assessment by means of sterile Doppler ultrasound probe
tine itself. Previously used assessment with intravenous fluorescein dye and Mesenteric artery revascularization is indicated to restore intestinal blood
1
an ultraviolet lamp is now rarely practiced clinically. 50 flow if adequate inflow is not achieved at embolectomy or ROMS. A
Except in very advanced cases where perforation has occurred or is number of surgical approaches are available, but in these fragile patients
imminent, revascularization should precede the resection of nonviable a quick, durable approach is required. Antegrade bypass requires a partial
bowel. In the presence of frank necrosis, quick segmental resection may supraceliac clamp. Retrograde bypass may derive inflow from the aorta or
be carried out using a gastrointestinal linear stapling device without common iliac artery. The choice of inflow vessel is influenced by the quality
undue delay of revascularization. On reperfusion, remarkable recovery and patency of the common iliac arteries which would have been identified
is often witnessed in seemingly unsalvageable segments, especially on the preoperative contrast CT scan. Either the right or left common iliac
important when near-total small bowel resection seems inevitable at can provide a suitable graft configuration. Should a vein be chosen second-
first inspection, with the consequent implications of lifelong parenteral ary to a contaminated field, the left iliac is preferred to avoid potential
nutrition therapy. Reperfusion of a profoundly ischemic intestine may kinking. If the infrarenal aorta is chosen, a nonocclusive clamp may be used.
cause dramatic systemic effects and may lead to catastrophic acidosis, In the absence of a suitable infrarenal inflow vessel, the supraceliac aorta
hyperkalemia, myocardial depression, and refractory shock. Caution may be approached through the lesser sac for inflow. The choice of arterial
must be exercised during reperfusion in the setting of an elderly, infirm, bypass conduit is a matter of debate. Prosthetic material is easy to handle,
or hypotensive patient. The initial approach to revascularization in obviates the need for autologous vein harvest, and reduces operative time.
most cases is an attempt at embolectomy; if satisfactory antegrade flow Indeed, even in the presence of moderate contamination, the risks of graft
cannot be achieved, then one proceeds to mesenteric artery bypass or infection remain low when polytetrafluoroethylene (PTFE) or antibiotic
retrograde open mesenteric stenting. soaked Dacron (rifampin 60 mg/mL) is used. In the presence of gross fecal
■ SUPERIOR MESENTERIC ARTERY EMBOLECTOMY contamination, an autologous vein graft is preferred, the reversed long
saphenous vein being most suitable. The outflow anastomosis is end to side
Embolectomy can be rapidly performed and quickly restores intestinal using the anterior arteriotomy employed for thrombectomy or ROMS.
may be exposed and controlled transperitoneally at the base of the trans- ■ INTESTINAL VIABILITY
blood flow with examination of the bowel. The superior mesenteric artery
verse mesocolon. It arises over the fourth part of duodenum and can be Clinical assessment by an experienced surgeon remains the most widely
difficult to localize when it is pulseless. It can be localized by palpation, practiced method to determine intestinal viability. A sensitivity of 82% and
assisted by a sterile Doppler probe in the bulky mesentery. After splitting a specificity of 91% were achieved using the following factors: presence
the mesentery in the line of the vessel, it is controlled with vascular loops. of visible pulsation in the mesenteric arcades, bleeding, color, and
Standard approach is via a transverse arteriotomy, but longitudinal open- peristalsis. Increasingly, most vascular surgeons now confirm their
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ing may help if vessel caliber is small or if bypass is expected. Proximal clinical findings with a sterile Doppler ultrasound flow detector (5 MHz),

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