Ileus vs obstruction
Formal Definition
A clinical and radiographic differentiation between two distinct causes of impaired gastrointestinal transit: ileus (also called paralytic ileus or adynamic ileus) is a failure of peristalsis without mechanical obstruction — usually from post-operative state, electrolyte derangements (hypokalemia, hypomagnesemia, hypercalcemia), medications (opioids, anticholinergics), intra-abdominal inflammation (peritonitis, pancreatitis, cholecystitis), or sepsis — characterized by absence of bowel sounds, abdominal distension without colicky pain, inability to tolerate PO, and gas/fluid pattern that often shows diffuse dilation of small and large bowel without a clear transition point; mechanical small bowel obstruction (SBO) is a true physical blockage from adhesions, hernias, tumors, or volvulus — typically presenting with colicky abdominal pain, vomiting (often bilious), abdominal distension, obstipation, and characteristic CT findings (transition point with dilated proximal bowel and decompressed distal bowel).
How It's Used on the Ward
"Ileus vs obstruction" — two distinct reasons the bowel stops working; ileus is "the plumbing is shut off" (no peristalsis from inflammation/drugs/electrolytes), obstruction is "the plumbing is blocked" (something physical is stopping it); both look like distension, N/V, and gas on imaging but the management differs completely — ileus is supportive care (NPO, NG decompression, correct the cause), obstruction may need surgery.
Example
""POD#3 from open colectomy, not passing flatus, abdominal distension, nausea. K 3.1 (low), on hydromorphone PCA. Abdominal X-ray: diffuse dilation of small and large bowel loops, gas throughout, no clear transition point. CT: distended loops without mechanical obstruction. Diagnosis: post-operative ileus, likely multifactorial from low K and opioids. Treatment: NPO, NG tube to low wall suction, correct potassium repletion, transition to scheduled Tylenol, hold opioid analgesia, encourage gum chewing, ambulation. Resolves over 24-72h. Contrast with: 70-year-old with prior abdominal surgery presenting with 12h of colicky abdominal pain, vomiting (bilious), distension, obstipation. CT abdomen: dilated small bowel loops with a transition point in the right lower quadrant and decompressed distal ileum. Diagnosis: small bowel obstruction from adhesions.""
Clinical Context
Key differentiators on history: (1) Ileus — typically absence of colicky pain, more constant discomfort if any, symptoms often slower onset, history of recent surgery or medication change. (2) Obstruction — colicky cramping pain (waves), earlier vomiting (especially with proximal SBO), obstipation (no stool/gas passing), more dramatic presentation. Exam: ileus — quiet abdomen (hypoactive or absent bowel sounds), distension without tenderness; obstruction — high-pitched tinkling sounds (early), hyperactive then quiet (late), focal tenderness near obstruction. Imaging: (1) Ileus — diffuse dilation of both small and large bowel, gas throughout including rectum, no transition point. (2) SBO — small bowel dilated with transition point and decompressed distal bowel, "string of pearls" sign (small gas bubbles trapped between valvulae conniventes in distended small bowel). (3) Large bowel obstruction — colonic distension with transition point (cecum most vulnerable to ischemia — diameter >12cm is concerning). Adynamic colon — colonic ileus without obstruction, common in elderly/bedridden/post-op. Treatment: ileus — supportive (NPO, NG decompression if vomiting, correct electrolytes, minimize opioids, encourage motility with ambulation/gum chewing/erythromycin if needed), almost never surgery. Mechanical SBO: trial of conservative management (NPO, NG, IV fluids) for partial SBO with mild symptoms; surgery for complete SBO or signs of strangulation/ischemia (fever, leukocytosis, lactic acidosis, peritonitis), closed-loop obstruction, or failed conservative management.