Definition of Small Bowel Ileus
Small bowel ileus is a functional obstruction characterized by impaired intestinal propulsion and failure of forward movement of intestinal contents without mechanical blockage, resulting from uncoordinated or attenuated intestinal muscle contractions. 1, 2
Core Pathophysiologic Features
Ileus represents a failure of the normal propulsive mechanisms of the small intestine, distinguished from mechanical obstruction by the absence of a physical barrier preventing passage of intestinal contents. 3, 2
The migrating myoelectric complex (MMC) becomes impaired, preventing the small bowel from clearing debris and predisposing to gut stasis and bacterial overgrowth. 4
Gut coordination is disrupted, and the presence of chyme in the small bowel can cause severe painful non-propulsive large contractions, particularly after eating. 4
Functional obstruction occurs due to uncoordinated or attenuated intestinal muscle contractions rather than mechanical blockage. 2
Clinical Manifestations
Gut stasis from failure of forward propulsion produces the characteristic clinical picture:
Abdominal distension develops as fluid accumulates from oral intake and normal gut secretions. 4
Large volume vomiting may occur, potentially faeculent and containing food debris from several days previously. 4
Hypoactive or absent bowel sounds are characteristic on physical examination, without visible peristalsis. 1
Constipation is often the first symptom of impaired propulsion. 4
Critical Distinguishing Features from Mechanical Obstruction
The absence of a distinct transition point between dilated and normal intestine is a key radiographic feature distinguishing ileus from mechanical obstruction. 1
Ileus affects mainly the small intestine, although it can be generalized, and occurs frequently after surgery, trauma, or with metabolic alterations. 1
Imaging studies do not demonstrate a mechanical blockage or fixed point of obstruction. 3, 2
Partial passage of intestinal contents may occur in some cases, unlike complete mechanical obstruction. 5
Temporal Classification
Chronic intestinal dysmotility is defined as more than 6 months of symptoms with features of pseudo-obstruction (nausea, vomiting, abdominal pain, distension, and often dilated bowel) in the absence of mechanical cause. 4
- Severe chronic intestinal dysmotility is present when associated malnutrition develops (BMI less than 18.5 kg/m² or more than 10% unintentional weight loss in last 3 months). 4
Common Pitfalls
Do not confuse ileus with mechanical obstruction - always obtain CT imaging with IV contrast to identify transition points, volvulus, or strangulation that would require surgical intervention. 6
Recognize that chronic intestinal pseudo-obstruction (CIPO) must be distinguished from true chronic mechanical obstruction, as CIPO represents persistent failure of intestinal propulsion due to dysmotility rather than mechanical blockage. 5
Avoid perpetuating ileus by continuing opioids and anticholinergics when alternative management strategies exist, as these medications directly impair intestinal motility. 6, 1