Gastrointestinal & Hepatic · Topic 16 of 26

Ileus & Acute Colonic Pseudo-obstruction

Gastrointestinal · motility failure

Ileus & Acute Colonic Pseudo-obstruction

A bowel that stops moving without a blockage. Decompress, give fluids and cut opioids; in Ogilvie syndrome, watch the cecum — 12 cm means perforation risk.

Key numbers

Cecum 12 cm or more: perforation riskcecum ≥ 12 cm

Neostigmine 2 mg IV, on a monitorneostigmine 2 mg IV

Keep potassium above 4 mEq/LK⁺ > 4 mEq/L

Ileus over 1 week suggests mechanical obstruction> 1 week

01 · The numberCecum 12 cm or more: perforation risk

A cecal diameter of 12 cm or more marks a substantially higher risk of perforation and early death and moves the patient past conservative care toward neostigmine or decompression.

02 · GiveNeostigmine 2 mg IV, on a monitor

Give neostigmine 2 mg IV over 3–5 minutes when the cecum is > 12 cm, pain is severe, or conservative care fails: patient supine on a bedpan, continuous ECG monitoring, atropine at the bedside.

03 · DoNPO, NG suction, IV fluids, fewer opioids

Treat ileus supportively: nothing by mouth, nasogastric suction for distension or vomiting, IV fluids and electrolytes, minimal sedation, and avoid opioids and anticholinergic drugs where possible.

What it is

Core idea

Ileus: peristalsis stops without mechanical obstruction must knowIleus is a temporary arrest of intestinal peristalsis with no mechanical blockage; abdominal surgery, especially with bowel handling, is the most common cause.

Ogilvie: colonic dilation without obstruction must knowAcute colonic pseudo-obstruction (Ogilvie syndrome) is acute colonic dilation, typically cecum and right colon, with no mechanical obstruction — usually in older, frail, postoperative or critically ill patients; CT excludes a mechanical cause.

Causes & risk factors

Why it happens

Other ileus causes: drugs, electrolytes, retroperitoneal processesBeyond surgery, ileus follows intra-abdominal or retroperitoneal inflammation or hematoma, hypokalemia, opioids, anticholinergics, and sometimes lower-lobe pneumonia, lower rib fractures or myocardial infarction.

Diagnosis & monitoring

Work-up

Keep potassium above 4 mEq/LCorrect electrolytes in every patient with ileus; keeping serum potassium above 4 mEq/L is especially important because hypokalemia itself causes ileus.

Postoperative recovery: small bowel, stomach, then colonAfter abdominal surgery the small bowel recovers within hours, gastric emptying in about 24 hours, and the colon last — often 48–72 hours or more.

No response: repeat neostigmine after 24 hoursMost responders pass flatus or stool within minutes of neostigmine (median 4 minutes in the trial; resolution in up to about 89%); a nonresponder can receive a second dose 24 hours after the first.

Do right now

In this order

First moves

NPO, NG suction, IV fluids, fewer opioids

→

Keep potassium above 4 mEq/LK⁺ > 4 mEq/L

→

Ogilvie: colonic dilation without obstruction

→

Neostigmine 2 mg IV, on a monitorneostigmine 2 mg IV

Why each step

NPO, NG suction, IV fluids, fewer opioidsTreat ileus supportively: nothing by mouth, nasogastric suction for distension or vomiting, IV fluids and electrolytes, minimal sedation, and avoid opioids and anticholinergic drugs where possible.

Keep potassium above 4 mEq/LCorrect electrolytes in every patient with ileus; keeping serum potassium above 4 mEq/L is especially important because hypokalemia itself causes ileus.

Ogilvie: colonic dilation without obstructionAcute colonic pseudo-obstruction (Ogilvie syndrome) is acute colonic dilation, typically cecum and right colon, with no mechanical obstruction — usually in older, frail, postoperative or critically ill patients; CT excludes a mechanical cause.

Neostigmine 2 mg IV, on a monitorGive neostigmine 2 mg IV over 3–5 minutes when the cecum is > 12 cm, pain is severe, or conservative care fails: patient supine on a bedpan, continuous ECG monitoring, atropine at the bedside.

Management

Orders

Alvimopan 12 mg around bowel resectionAlvimopan, a peripherally acting mu-opioid antagonist, speeds GI recovery after bowel resection with primary anastomosis: 12 mg 30 minutes–5 hours before surgery, then 12 mg twice daily for up to 7 days (max 15 doses).

Cecum under 12 cm: supportive care firstWith cecum under 12 cm and no peritonitis, start conservative care: treat the cause, stop offending drugs, NG and rectal tube decompression, correct electrolytes, and repeat abdominal films and labs every 12–24 hours.

Colonoscopic decompression if neostigmine failsColonoscopic decompression, often leaving a decompression tube, is for patients who fail or cannot receive neostigmine; it is technically difficult, with about a 2% perforation rate.

Surgery for perforation, ischemia or failed decompressionReserve surgery for perforation, ischemia or peritonitis, or failure of medical and endoscopic decompression; operative morbidity and mortality are high, especially in frail older patients.

Red flags & don'ts

Avoid harm

Neostigmine contraindications: obstruction, bradycardia, recent MI, asthma avoidDo not give neostigmine with mechanical obstruction, perforation or peritonitis; recent myocardial infarction, bradycardia or arrhythmia, asthma or bronchospasm, and beta-blocker therapy are contraindications or strong cautions.

The rules

Know these

Ileus over 1 week suggests mechanical obstructionIleus that persists more than 1 week probably has a mechanical obstructive cause; reassess (contrast-enhanced CT helps separate the two) and consider laparotomy.

Postoperative ileus or colonic pseudo-obstruction?

Commonly confused

What stops	Whole gut; colon recovers last (48–72 h)
Main danger	Missed mechanical obstruction if > 1 week
First treatment	NPO, NG suction, IV fluids, K⁺ > 4, fewer opioids
Drug	Alvimopan around bowel resection (prevention)
Escalation	Consider laparotomy if ileus lasts > 1 week

Commonly confused

Tell apart

Ileus pain is vague, not colickyIleus causes distension, nausea and vague discomfort with a quiet abdomen; colicky pain suggests mechanical obstruction. When films cannot separate them, contrast-enhanced CT helps.

More detail

Reference

Show 3 reference facts

Colonic perforation in pseudo-obstruction carries reported mortality up to 40%, and frailty independently predicts 30-day death.

In postoperative ileus gas collects more in the colon than the small bowel; new small-bowel gas accumulation after surgery often signals a complication such as obstruction or peritonitis.

Alvimopan is contraindicated after more than 7 consecutive days of therapeutic opioids and is restricted to enrolled hospitals under a REMS for short-term use because of a myocardial infarction signal with long-term use.

Pearl

No blockage, no peristalsis: decompress, replete potassium, cut the opioids — and measure the cecum every day in Ogilvie syndrome.

Sources · Merck Manual Professional — Ileus (Jul 2024) · Ten-year management of acute colonic pseudo-obstruction in a single UK center: a retrospective cohort study. Ann Med Surg 2026 (cecal diameter ≥ 12 cm; guideline-recommended pathway) · Sackmaster S et al. ASGE advanced practice provider case of the month: acute colonic pseudo-obstruction. iGIE 2024 (summarizes the 2020 ASGE guideline) · Liu et al. Efficacy and Safety of Neostigmine and Decompressive Colonoscopy for Acute Colonic Pseudo-Obstruction. Gastroenterology Research (cites ASGE guideline: neostigmine after 72 h failed supportive care) · Alvimopan capsules prescribing information — DailyMed · Ponec RJ, Saunders MD, Kimmey MB. Neostigmine for the treatment of acute colonic pseudo-obstruction. N Engl J Med 1999;341:137–141 (abstract via Europe PMC: 2.0 mg IV after ≥ 24 h failed conservative care) · Neostigmine methylsulfate injection prescribing information (American Regent) — contraindications: peritonitis or mechanical obstruction; cautions in CAD, arrhythmia, recent ACS · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).