Step 2 CK · Surgery

Bowel Obstruction & Ischemia

Name: Bowel Obstruction & Ischemia
Creator: Veli Bakalov, MD

Drip-and-suck versus the knife, and the pain that is out of proportion

Surgery·General Surgery·4 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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SBO: adhesions from prior surgery are the #1 cause, then hernia (#1 without prior surgery), then malignancy; LBO: colorectal cancer, then volvulus, then diverticular stricture.
SBO has early bilious vomiting, less distension, and valvulae conniventes across the full lumen; LBO has late feculent vomiting, more distension, and haustra; dilation >3 cm small bowel, >6 cm colon, >9 cm cecum.
Simple partial adhesive SBO → NPO, nasogastric decompression, IV fluids, electrolytes ("drip and suck"); operate for complete obstruction, strangulation, closed loop, or failure to improve.
Strangulation signs (fever, tachycardia, leukocytosis, peritoneal signs, rising lactate or acidosis, continuous pain) mandate surgery; closed-loop obstruction (volvulus, incarcerated hernia) is a surgical emergency.
Sigmoid volvulus (elderly, institutionalized; coffee bean pointing to the RUQ) → endoscopic detorsion plus rectal tube, then sigmoid colectomy during the same admission; cecal volvulus (younger) → right hemicolectomy or cecopexy.
Acute mesenteric ischemia = pain out of proportion to a benign exam; SMA embolism from atrial fibrillation is most common; lactate rises late; CT angiography diagnoses.
Mesenteric ischemia treatment: anticoagulation, embolectomy or revascularization, resection of necrotic bowel, second-look laparotomy.
Ischemic colitis: watershed zones (splenic flexure, rectosigmoid) in older adults → crampy pain, bloody diarrhea, thumbprinting; usually self-limited with supportive care.
Ogilvie syndrome: massive colonic dilation without mechanical cause (postoperative, elderly, opioids, electrolytes) → correct electrolytes, stop opioids; neostigmine ± decompression if the cecum is >10–12 cm.

Small- vs large-bowel obstruction

Mechanical obstruction presents with colicky pain, vomiting, distension, and obstipation. Bowel sounds are high-pitched and tinkling early, then absent as the bowel fatigues. Vomiting drives dehydration and a hypokalemic, hypochloremic metabolic alkalosis.

SBO vs LBO

Feature	Small bowel	Large bowel
Leading causes	Adhesions (prior surgery), then hernias, then malignancy	Colorectal cancer, then volvulus, then diverticular stricture
Vomiting	Early, bilious	Late, feculent
Distension	Less	More
Mucosal folds on film	Valvulae conniventes cross the full lumen	Haustra cross only part of the width
Dilation threshold	>3 cm	Colon >6 cm, cecum >9 cm

No prior surgery and an obstruction? Examine every hernia orifice, since hernia is then the leading cause.

The colon can close its own loop. A competent ileocecal valve blocks decompression back into the small bowel, turning a distal colonic obstruction into a closed loop that stretches the cecum.

Films dilate, CT explains. Plain films show dilated loops with air-fluid levels in a step-ladder pattern and a string-of-pearls sign. CT identifies the transition point, the cause, a closed-loop configuration, and signs of ischemia.

Drip and suck, or the OR

Simple, partial adhesive SBO is managed conservatively, and most resolve. A water-soluble contrast challenge helps predict success: contrast reaching the colon within 24 hours suggests the obstruction will settle.

NPO and nasogastric decompressionRelieve distension and vomiting.
IV fluids and electrolytesCorrect dehydration, hypokalemia, and alkalosis.
Serial exams and labsWatch for signs of strangulation.
OperateComplete obstruction, strangulation, closed loop, or failure to improve.

Simple adhesive SBO: drip and suck

Closed loop strangles fast. A closed-loop obstruction blocks the bowel at two points (volvulus, incarcerated hernia), trapping a segment that rapidly progresses to strangulation, ischemia, and perforation. It is a surgical emergency, not a candidate for observation.

Strangulation flips you to the OR: fever, tachycardia, leukocytosis, peritoneal signs, rising lactate or metabolic acidosis, and continuous rather than colicky pain. Any of these converts management from conservative to emergent surgery.

Volvulus

Sigmoid vs cecal volvulus

Feature	Sigmoid volvulus	Cecal volvulus
Patient	Elderly, institutionalized, chronically constipated	Younger patients
Imaging	Coffee-bean sign pointing to the RUQ; bird's beak on contrast enema	Dilated cecum displaced toward the left upper abdomen
First treatment	Endoscopic detorsion (flexible sigmoidoscopy) plus a rectal tube	Surgery: right hemicolectomy or cecopexy
Afterward	Sigmoid colectomy during the same admission if fit for surgery, because recurrence is high	Definitive at the first operation

Sigmoid scopes, cecal cuts. Peritonitis or gangrenous mucosa at endoscopy means emergent sigmoid resection instead.

Mesenteric ischemia and ischemic colitis

Pain out of proportion. Acute mesenteric ischemia produces severe pain with a soft, benign-appearing early exam. A rising lactate signals infarction and is a late sign; peritonitis follows as the bowel necroses.

Arterial occlusionEmbolus or thrombus.
Pain out of proportionBenign early exam.
Rising lactateInfarction; a late sign.
PeritonitisBowel necrosis.

Mesenteric ischemia course

Subtypes of acute mesenteric ischemia

Subtype	Setting	Onset
SMA embolism (most common)	Atrial fibrillation or other cardiac source	Sudden
SMA thrombosis	Atherosclerosis, often with prior intestinal angina	Gradual
Nonocclusive	Low flow: shock, heart failure, vasopressors	In the critically ill
Mesenteric venous thrombosis	Hypercoagulable state	Often subacute

Angiography, then revascularize. CT angiography is the diagnostic test. Treat with anticoagulation, embolectomy or revascularization, resection of necrotic bowel, and a second-look laparotomy to reassess viability. Venous thrombosis is treated mainly with anticoagulation, and nonocclusive ischemia by restoring perfusion.

Chronic mesenteric ischemia (intestinal angina) causes postprandial pain, food fear, and weight loss.

Ischemic colitis hits the watershed zones (splenic flexure, rectosigmoid) in older adults, presenting with crampy pain, bloody diarrhea, and thumbprinting on imaging. Unlike acute mesenteric ischemia, it is usually low-grade and self-limited and is managed supportively.

Pseudo-obstruction and ileus

Ogilvie syndrome (acute colonic pseudo-obstruction) is massive colonic dilation with no mechanical cause, seen postoperatively, in the elderly, and with electrolyte derangements or opioids. Exclude a mechanical lesion, correct electrolytes, and stop offending drugs. If the cecum exceeds 10–12 cm, give neostigmine (monitor for bradycardia) and consider colonoscopic decompression.

A cecal diameter over 10–12 cm signals impending perforation: by the law of Laplace, the widest segment has the highest wall tension and perforates first.

Paralytic ileus mimics obstruction with distension and no flatus but has no mechanical lesion; bowel sounds are hypoactive or absent, and gas is spread through both small bowel and colon. Opioids and electrolyte abnormalities aggravate it. Management is supportive: minimize opioids, correct electrolytes, and encourage mobilization.