What is Intestinal Obstruction
Intestinal obstruction is an interruption in the forward flow of intestinal contents that can occur at any point along the gastrointestinal tract, caused either by a mechanical blockage (such as adhesions, hernias, or tumors) or by failure of coordinated intestinal propulsion without a physical obstruction (pseudo-obstruction). 1, 2
Two Main Categories
Mechanical Obstruction
- Physical blockage preventing passage of intestinal contents through the bowel 1, 3
- Most commonly caused by intra-abdominal adhesions (55-75% of small bowel cases), malignancy (60% of large bowel cases), or hernias 4, 1
- Can occur from volvulus, intussusception, strictures from radiation or inflammatory bowel disease, or foreign bodies 5, 2
Functional Obstruction (Pseudo-obstruction)
- Failure of coordinated intestinal propulsion giving symptoms and signs of obstruction without a mechanical cause 5
- Results from disorders of intestinal smooth muscle (myopathy), neural control (neuropathy), or both 5
- Distinguished from simple ileus by duration (chronic pseudo-obstruction defined as >6 months of symptoms) 5
Clinical Presentation
Cardinal Symptoms
- Colicky abdominal pain that worsens with peristaltic attempts to overcome the obstruction 4
- Nausea and vomiting (more prominent and earlier in small bowel obstruction; green/yellow vomit suggests proximal obstruction, feculent vomit suggests distal obstruction) 5, 4
- Absence of flatus (90% of cases) and absence of bowel movements (80.6% of cases) 4
- Abdominal distension (65.3% of cases) and bloating 4
Physical Examination Findings
- Abdominal distension with tympany to percussion (positive likelihood ratio of 16.8) 4, 1
- Hyperactive or absent bowel sounds depending on stage 4, 1
- Visible peristalsis in thin patients 4
- Abdominal tenderness (localized or diffuse depending on complications) 4
Warning Signs of Complications (Strangulation/Ischemia)
These findings mandate urgent surgical evaluation: 4, 6
- Fever, tachypnea, tachycardia, and confusion 4
- Intense pain unresponsive to analgesics 4
- Diffuse abdominal tenderness, guarding, or rebound tenderness 4
- Absent bowel sounds 4
- Signs of shock: hypotension, cool extremities, mottled skin, oliguria 4
- Laboratory findings: leukocytosis, elevated lactate, low bicarbonate/arterial pH, elevated amylase 4
Pathophysiology
When obstruction occurs, fluid and gas accumulate proximal to the blockage as the bowel continues to secrete fluid and swallowed air cannot pass distally 6. This leads to:
- Progressive bowel distension 1, 2
- Increased intraluminal pressure causing bowel wall edema 2
- Potential compromise of blood flow leading to mucosal ischemia, necrosis, and perforation if untreated 6
- Fluid sequestration causing dehydration and electrolyte abnormalities 3
Key Diagnostic Distinctions
Small vs. Large Bowel Obstruction
Small bowel obstruction: 4
- Vomiting occurs earlier and more frequently
- Adhesions are the most common cause (55-75%)
- History of prior abdominal surgery in 85% of adhesive cases
Large bowel obstruction: 4
- More gradual symptom development
- Less frequent vomiting
- Cancer is the most common cause (60%)
- May have history of bloody stools, chronic constipation, or rectal bleeding
Mechanical vs. Functional (Pseudo-obstruction)
Key distinguishing feature: In mechanical obstruction, imaging shows a distinct transition point between dilated and normal-sized bowel 5. In pseudo-obstruction, there is no transitional zone despite dilated bowel and obstructive symptoms 5.
Common Pitfalls
- Mistaking incomplete obstruction with watery diarrhea for gastroenteritis - when obstruction resolves intermittently, diarrhea follows as secreted fluid passes through 5, 4
- Overlooking obstruction in elderly patients where pain may be less prominent 4
- Missing adhesive obstruction when imaging is performed after spontaneous resolution - obtain CT during acute pain episodes 5
- Failing to recognize opioid-induced bowel dysfunction which can mimic or contribute to obstruction 5