Bowel Obstruction

GI NOTES

Bowel Obstruction

Key points

Adhesions cause most small bowel obstructions; cancer and volvulus cause most large bowel obstructions.
CT with IV contrast is the key test: it confirms obstruction, finds the transition point and shows signs of ischemia.
Strangulation, peritonitis or closed-loop obstruction need surgery now.
Uncomplicated adhesive obstruction: bowel rest, nasogastric decompression, fluids and a water-soluble contrast challenge.
Sigmoid volvulus is usually untwisted endoscopically first; cecal volvulus needs surgery.

1. Small vs large bowel obstruction

	Small bowel	Large bowel
Main causes	Adhesions, hernias, Crohn’s strictures, tumors, gallstone ileus	Colorectal cancer, volvulus, diverticular stricture
Symptoms	Early vomiting, colicky central pain, distension	Gradual distension, constipation and no gas, late vomiting
Imaging	Dilated loops above 3 cm, air-fluid levels, collapsed bowel beyond a transition point	Colon above 6 cm (cecum above 9 cm); “coffee bean” sign in sigmoid volvulus
Danger	Strangulation, closed loop	Cecal perforation, especially with a competent ileocecal valve

2. Adhesive small bowel obstruction

FIGURE: MANAGING ADHESIVE SMALL BOWEL OBSTRUCTION

Suspected SBO: CT with IV contrast, lactate, electrolytes

Ischemia, peritonitis or closed loop: surgery now

No danger signs: nil by mouth, NG tube, IV fluids, correct electrolytes

Water-soluble contrast by NG tube; X-ray at about 8 to 24 hours

Contrast in colon: likely to resolve; start diet

No contrast in colon, or no improvement by about 72 hours: surgery

Original diagram based on the Bologna (WSES) 2017 guidelines.

Signs of strangulation

Clinical: constant (not colicky) pain, fever, tachycardia, peritonism, rising lactate and WBC. None of these is reliable alone.
CT: reduced bowel wall enhancement, mesenteric edema or fluid, free fluid, bowel wall thickening, pneumatosis or portal venous gas, closed loop with two transition points, “whirl” sign.

3. Large bowel obstruction

Malignant obstruction: surgery (resection, or a stoma) or a self-expanding metal stent as a bridge to surgery or for palliation in left-sided tumors. Stenting is avoided in suspected perforation.
Sigmoid volvulus: endoscopic detorsion (flexible sigmoidoscopy) with a rectal tube if no gangrene; plan elective sigmoid resection in the same admission because recurrence is common.
Cecal volvulus: surgery (right colectomy); endoscopy is rarely successful.
Gangrene, perforation or peritonitis at any site: emergency surgery.

4. Acute colonic pseudo-obstruction (Ogilvie syndrome)

Massive colonic dilation with no mechanical blockage, usually in hospitalized patients after surgery, trauma or severe illness, or with opioids and electrolyte problems.
First rule out mechanical obstruction with CT.
Supportive care: treat the cause, stop opioids and anticholinergics, correct potassium and magnesium, NG and rectal tubes, mobilize.
Neostigmine (2 mg IV over 3 to 5 minutes, with cardiac monitoring and atropine at hand) if the cecum is above about 10 to 12 cm or there is no response to 24 to 48 hours of supportive care.
Colonoscopic decompression if neostigmine fails or is contraindicated; surgery for perforation or ischemia.

Self-check questions

What is the most common cause of small bowel obstruction?
Adhesive SBO, no danger signs. Water-soluble contrast reaches the colon at 12 hours. What does this mean?
Coffee-bean sign, no peritonitis. What is the first treatment?
Cecum 13 cm with no mechanical blockage after hip surgery, no response to 48 hours of supportive care. Next step?

Answers: (1) Adhesions. (2) The obstruction is likely to resolve without surgery. (3) Endoscopic detorsion, then elective sigmoid resection. (4) IV neostigmine with cardiac monitoring.

References

ten Broek RPG, Krielen P, Di Saverio S, et al. Bologna guidelines for diagnosis and management of adhesive small bowel obstruction (ASBO): 2017 update of the evidence-based guidelines from the World Society of Emergency Surgery ASBO working group. World J Emerg Surg. 2018;13:24.
Pisano M, Zorcolo L, Merli C, et al. 2017 WSES guidelines on colon and rectal cancer emergencies: obstruction and perforation. World J Emerg Surg. 2018;13:36.
Alavi K, Poylin V, Davids JS, et al. The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Colonic Volvulus and Acute Colonic Pseudo-Obstruction. Dis Colon Rectum. 2021;64(9):1046-1057.
Naveed M, Jamil LH, Fujii-Lau LL, et al. American Society for Gastrointestinal Endoscopy guideline on the role of endoscopy in the management of acute colonic pseudo-obstruction and colonic volvulus. Gastrointest Endosc. 2020;91(2):228-235.

For educational purposes only. This note does not replace clinical judgment or local protocols. Check doses against current labeling and institutional guidance.