Colon and Small Bowel—Acute Bowel Ischemia

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Colon and Small Bowel—Acute Bowel Ischemia

Concept

Pathogenesis includes multiple etiologies but can generally be broken down into occlusive and nonocclusive types.

DDx for a patient with suspected colonic ischemia should also include other colonic disorders such as ulcerative coli- tis, infectious colitis, and pseudomembranous colitis. A breakdown of important types of occlusive and nonocclu- sive ischemia follows:

Occlusive Nonocclusive

Embolism Hypovolemia

Thrombosis Cardiac failure/cardiogenic Vascular compression shock

AAA repair Hypotension

Watershed areas vulnerable to low flow states in the colon: Griffith’s point (splenic flexure) and Sudeck’s point (rectosigmoid) for nonocclusive ischemia.

Way Question May be Asked?

“Called to see a 54 y/o male POD#2 after an uncompli- cated AAA repair with a massive bloody bowel move- ment. What do you want to do?” Situation could also be after recent open heart surgery, recent MI, or a more chronic form with post-prandial pain for several months with associated weight loss. Remember “pain out of pro- portion to physical exam” is classic for acute bowel ischemia. Try to separate generalized intestinal ischemia from colonic ischemia and occlusive from low flow states.

How to Answer?

History

Risk factors: valvular disease, CAD, hypercoagulable state, cardiac arrhythmias

Classic: abrupt onset abdominal pain, diarrhea, hema- tochezia

Recent surgery (AAA, bypass) Recent MI (embolus)

Classic triad of: fever, abdominal pain, and heme + stools Abrupt onset of: pain, diarrhea, hematochezia

Physical Exam

“Toxic” appearance, shock, acidosis, leukocytosis Keep in mind: “Pain out of proportion to physical

exam”

Peritonitis Heme + Stool

Gross blood (usually late finding) Irregular heart rate (a. fib)

Diagnostic Tests

Full labs (amylase and lactate also helpful)—acidosis a late finding

EKG (r/o a. fib)

Abd x-ray: free air, pneumatosis intestinalis, portal vein air CT scan: “thumb printing”, bowel wall thickening,

pneumatosis, portal vein air

Colonoscopy: mucosal edema, submucosal hemor- rhage, mucosal ulceration, bluish-black discol- oration, areas of black nonviable mucosa, may be skip areas (keep air insufflation to a minimum, may prep with gentle tap water enema)

Arteriography (to evaluate small bowel):

Could see SMA embolus Could see SMA thrombosis

Could see normal proximal vessels but then distal spasm

Surgical Treatment

(1) Decide if this is acute small bowel mesenteric occlu- sion vs. colonic ischemia

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(2) Initially

Volume support (may need SGC), ICU, O

, bowel rest, NGT, Foley

Serial labs/exams

Abx when remarkable endoscopic findings or evi- dence of toxemia

(3) If colonic ischemia improves

colonoscopy 6–8 weeks after for evaluate for resolu- tion/sequelae (stricture) 5% pt with recurrent episodes

(4) If becomes toxic or peritoneal signs Resuscitate pt and prepare for OR In OR:

Control contamination

Palpation of celiac, SMA, IMA pulses

Pattern of ischemia may suggest etiology (com- plete vs. patchy)

Hand-held Doppler, Fluorescein injection/

Wood’s lamp, warm packs

Left colon involvement: resection w/colostomy + mucous fistula or Hartmann’s pouch

Right colon involvement: resection with ileostomy and mucous fistula

Second look laparotomy if any question of via- bility

(5) For small bowel ischemia, if pt toxic or positive angiogram (angiogram helpful in situations of sus- pected small bowel ischemia, not for ischemic coli- tis), proceed to OR:

Prep access to greater saphenous vein in thigh Expose SMA

(a) SMA embolus (proximal braches of SMA are spared)

Seen 3–8 cm from SMA origin (spares first por- tion of jejunum only)

Embolectomy through transverse arteriotomy Heparin post-op

“Second look procedure” within 24 h (b) SMA thrombosis

Embolectomy to SMA Assess flow

If poor, SVG between infrarenal aorta and SMA

(can use suprarenal aorta and pass graft behind pancreas to SMA)

Heparin post-op

Resect nonviable segments + “second look pro- cedure” within 24 h

Facts on Aortic Surgery:

Ischemia complicates of 1–2% elective cases 50% mortality rate

Early colonoscopy

reimplantation IMA when:

severe SMA dx, enlarged IMA, loss of Doppler in sigmoid mesentery, hx of prior colon resec- tion, poor IMA back bleeding (stump pres- sure < 40 mmHg)

If need to take back to OR, perform end colostomy and Hartman pouch

Common Curveballs

Pt will have had prior surgery Pt will have SMA embolus Pt will have SMA thrombosis Will be SMV thrombosis

Pt will need resuscitation pre-op +/− SGC Pt will have necrotic bowel at second look Pt will have hypercoagulable syndrome

Pt will have had recent AAA repair with worry about graft contamination

Whole small bowel will initially appear necrotic Asked how to identify SMA (elevate transverse colon,

follow middle colic to SMA, will need to make inci- sion in peritoneum of mesentery, artery is medial to SMV)

Pt will return 6 weeks after colonic ischemia treated non-operatively with stricture

Strikeouts

Performing intestinal anastomosis in setting of ischemia/contamination

Not performing second look if question viability at 1st operation

Not knowing how to deal with SMA embolus/throm- bosis

Not resuscitating pt pre-op but taking straight to OR Discussing urokinase infusion for pt with embolic

occlusion of mesenteric vessels or colonic ischemia Delaying on operation when pt is toxic

Not resecting necrotic bowel

Not understanding difference between acute mesenteric ischemia and colonic ischemia

Strikeouts 13

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