Gastrointestinal & Hepatic · Topic 14 of 26

Small & Large Bowel Obstruction

Gastrointestinal · surgical abdomen

Small & Large Bowel Obstruction

Decompress, resuscitate and get a CT — then hunt for strangulation, which turns a nonoperative obstruction into an emergency operation.

Key numbers

Constant pain and tenderness: suspect strangulationinfarction in ~6 h

Adhesive SBO: up to 72 hours nonoperativetrial ≤ 72 h

Water-soluble contrast not in colon by 24 hourscolon by 24 h

Cecal perforation risk at 13 cmcecum ≥ 13 cm

01 · Look forConstant pain and tenderness: suspect strangulation

Strangulation can infarct bowel within about 6 hours: suspect it when colicky pain turns severe and steady, with fever, tachycardia, tenderness or peritonitis, leukocytosis or acidosis — examination misses about half of cases.

02 · DoNasogastric decompression, IV fluids, electrolytes, surgeon

Admit, keep NPO, decompress with nasogastric suction, resuscitate with 0.9% saline or lactated Ringer's, replace sodium and potassium lost to vomiting, place a urinary catheter for output, and involve a surgeon from the start.

03 · DoAdhesive SBO: up to 72 hours nonoperative

Adhesive small bowel obstruction without peritonitis, strangulation or ischemia gets nonoperative management (NPO, decompression, fluids) for up to 72 hours; failure to resolve, or any sign of ischemia, means surgery.

Causes & risk factors

Why it happens

Adhesions, hernias and tumors cause most obstructions must knowAdhesions, hernias and tumors cause most mechanical obstruction; small bowel obstruction without prior surgery or a hernia suggests a tumor, and large bowel obstruction is usually left colon cancer, sigmoid diverticulitis or volvulus.

Presentation

What you'll see

Sigmoid volvulus: coffee-bean sign on radiographSigmoid volvulus usually shows a coffee-bean loop on plain abdominal radiographs (a bird-beak on contrast enema); get CT if the diagnosis is in doubt or ischemia or perforation is suspected, plus blood gas and lactate.

Diagnosis & monitoring

Work-up

Cecal perforation risk at 13 cmObstructed bowel perforates in an ischemic segment (typically small bowel) or, in large bowel obstruction, at the cecum — the risk is high once cecal diameter reaches 13 cm or more.

Do right now

In this order

First moves

Nasogastric decompression, IV fluids, electrolytes, surgeon

→

CT: look for closed loop and ischemia

→

Adhesive SBO: up to 72 hours nonoperativetrial ≤ 72 h

Why each step

Nasogastric decompression, IV fluids, electrolytes, surgeonAdmit, keep NPO, decompress with nasogastric suction, resuscitate with 0.9% saline or lactated Ringer's, replace sodium and potassium lost to vomiting, place a urinary catheter for output, and involve a surgeon from the start.

CT: look for closed loop and ischemiaCT is the preferred imaging when cause or management is uncertain: it predicts strangulation and need for surgery with about 90% accuracy; a closed loop, bowel ischemia or free fluid means surgery without delay.

Adhesive SBO: up to 72 hours nonoperativeAdhesive small bowel obstruction without peritonitis, strangulation or ischemia gets nonoperative management (NPO, decompression, fluids) for up to 72 hours; failure to resolve, or any sign of ischemia, means surgery.

Management

Orders

Water-soluble contrast not in colon by 24 hoursA water-soluble contrast challenge in adhesive obstruction is predictive and may be therapeutic: contrast that has not reached the colon on a radiograph 24 hours later strongly predicts failure of nonoperative management.

Complete obstruction or ischemia: operate earlyComplete small bowel obstruction is treated with early laparotomy after a brief 2–3 hour resuscitation; give antibiotics against bowel flora (eg, cefoxitin) before operating when ischemia is suspected.

Detorse sigmoid volvulus endoscopically, then resectWithout ischemia or perforation, decompress sigmoid volvulus with urgent flexible endoscopy (60–95% success), then offer sigmoid colectomy during the same admission because it recurs in about half without resection.

Failed detorsion or gangrene: urgent sigmoid resectionUrgent sigmoid resection is required when endoscopic detorsion fails or the colon is nonviable or perforated.

Cecal volvulus needs surgery, not endoscopyColonoscopy rarely reduces a cecal volvulus; treat it surgically with resection and anastomosis (cecopexy or cecostomy in a frail patient).

Red flags & don'ts

Avoid harm

Examine every hernia site and surgical scar complicationAbout 25% of small bowel obstructions strangulate, usually from a hernia, volvulus or intussusception, so examine groins and every scar for an incarcerated hernia; strangulation is rare in large bowel obstruction except volvulus.

Small or large bowel obstruction?

Commonly confused

Usual cause	Adhesions and hernias
Onset and vomiting	Rapid; early vomiting, periumbilical cramps
Strangulation	About 25% (hernia, volvulus, intussusception)
Perforation site	Ischemic segment

More detail

Reference

Show 6 reference facts

About 85% of partial small bowel obstructions resolve without surgery, whereas most complete obstructions need an operation.

Baseline labs: CBC, lactate, electrolytes, CRP and BUN/creatinine. Leukocytosis and acidosis suggest strangulation but may be absent; CRP > 75 and WBC > 10,000 hint at peritonitis.

Plain films show dilated small bowel loops in a ladder pattern with air-fluid levels; loops may be absent in proximal or closed-loop obstruction, and gas in the bowel wall (pneumatosis) means gangrene.

Gallstone ileus is treated by removing the stone through an enterotomy; cholecystectomy is not needed at the same operation.

Obstructing colon cancer is treated by resection with or without a stoma, or a diverting colostomy first; endoscopic stenting palliates patients unfit for surgery but as a bridge to curative surgery remains controversial.

Early postoperative or recurrent adhesive obstruction without peritoneal signs can be managed with nasogastric decompression first; malignant small bowel obstruction may be palliated with a venting gastrostomy or stent.

Pearl

Never let the sun set on a strangulated bowel — strangulating obstruction can infarct within about 6 hours.

Sources · Merck Manual Professional — Intestinal Obstruction · Bologna guidelines for diagnosis and management of adhesive small bowel obstruction (ASBO): 2017 update of the WSES ASBO working group. World J Emerg Surg 2018 · WSES consensus guidelines on sigmoid volvulus management. World J Emerg Surg 2023 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).