Intestinal Obstruction

Intestinal obstruction is the partial or complete blockage of the forward passage of bowel contents and is one of the commonest surgical emergencies. NEET PG loves this topic for its classic radiology (ladder pattern, coffee-bean sign), the simple-vs-strangulated distinction, and the conservative-vs-operate decision.

Definition & classification

Intestinal obstruction = arrest of the aboral propulsion of intestinal contents. It is broadly split into mechanical (a physical block) and functional / adynamic (failure of peristalsis, e.g. paralytic ileus, pseudo-obstruction).

A clean classification framework for exams:

Basis	Types	Key point
Mechanism	Mechanical vs Functional (ileus / Ogilvie)	Ileus = no peristalsis, no mechanical block
Level	High small bowel, low small bowel, large bowel	Higher = more vomiting, less distension
Extent	Partial vs Complete	Complete = no flatus/faeces (obstipation)
Blood supply	Simple vs Strangulated	Strangulation = ischaemia → gangrene; surgical emergency
Lumen relation	Intraluminal, Intramural, Extraluminal	Bezoar/gallstone vs tumour/stricture vs adhesion/hernia
Mode	Acute, Chronic, Acute-on-chronic, Subacute	Large bowel cancer is classically chronic/acute-on-chronic

A special and dangerous subtype is the closed-loop obstruction, where the bowel is occluded at two points (e.g. volvulus, obstructed loop in a hernia, or a competent ileocaecal valve in colonic obstruction). The trapped segment cannot decompress, distends rapidly, and progresses quickly to strangulation and perforation.

High-yield: A competent ileocaecal valve converts a large bowel obstruction into a closed-loop obstruction — the caecum (thinnest wall, largest diameter per Laplace's law) is the commonest site of perforation. Caecal diameter > 12 cm on plain film signals impending rupture.

Etiology

Causes differ by age and by bowel segment — a favourite MCQ axis.

Commonest causes overall (adults):

1. Adhesions (postoperative) → most common cause of small bowel obstruction (SBO) in adults.
2. Hernias (external — inguinal/femoral; or internal) → 2nd most common SBO cause; commonest cause in patients without prior surgery.
3. Malignancy → most common cause of large bowel obstruction (LBO); usually colorectal carcinoma.

Age group	Most common cause
Neonate	Congenital atresia, malrotation/volvulus, meconium ileus, Hirschsprung
Infant (3 mo–2 yr)	Intussusception (ileocolic)
Young child	Worms (Ascaris), Meckel's diverticulum, intussusception
Adult	Adhesions > hernia > malignancy
Elderly	Malignancy, sigmoid volvulus, diverticular stricture, gallstone ileus

High-yield: Adhesions = commonest cause of SBO in operated patients; obstructed hernia = commonest cause in those never operated. Don't forget to examine all hernial orifices in every obstruction case — a missed femoral hernia is a classic exam trap (femoral hernias most often present as obstruction/strangulation in elderly women).

Mnemonic for SBO causes — "AHA": Adhesions, Hernias, (tumours And) others — or the broader "ABC": Adhesions, Bands/Bulges (hernias), Cancer/Crohn's.

Pathophysiology

Proximal to the block, gas (mostly swallowed nitrogen) and fluid accumulate → bowel distends → increased intraluminal pressure → impaired venous return → mural oedema → third-space fluid sequestration into lumen and bowel wall → hypovolaemia, dehydration, electrolyte loss.

Sequence (flow): Obstruction → proximal distension (gas + fluid) → ↑ intraluminal pressure → venous congestion → wall oedema & arterial compromise → mucosal ischaemia → bacterial translocation → gangrene → perforation → peritonitis → septic shock.

Metabolic picture: vomiting and sequestration cause hypokalaemic, hypochloraemic metabolic alkalosis (esp. high/proximal obstruction). Late strangulation with lactic acidosis shifts this toward metabolic acidosis — a marker of ischaemia.

High-yield: Strangulation is suggested by — continuous (rather than colicky) pain, tachycardia, fever, localised tenderness/guarding, leukocytosis, raised lactate/CRP, and a constant non-shifting tender mass. These overturn a "wait-and-watch" plan toward urgent surgery.

Clinical features

The classic tetrad — pain, vomiting, distension, absolute constipation (obstipation) — but the order and prominence localise the level:

Feature	High (proximal) SBO	Low SBO	LBO
Vomiting	Early, profuse, bilious	Later, may be faeculent	Late or absent
Distension	Minimal	Central, marked	Marked, peripheral/flanks
Pain	Upper abdomen, frequent colic (every 3–5 min)	Periumbilical colic	Lower abdomen, colic every 10–15 min
Constipation	Late	Late	Early/absolute

• Bowel sounds: early — exaggerated, high-pitched, tinkling ("borborygmi"); late or in strangulation/ileus — silent.
• Visible peristalsis and a tympanitic distended abdomen support mechanical obstruction.
• In paralytic ileus: distension with absent bowel sounds and no colic — pain is dull and continuous.

High-yield: Faeculent vomiting (foul, due to bacterial overgrowth in stagnant small bowel content) indicates long-standing distal SBO — it is NOT the same as vomiting actual faeces.

Investigations

Plain erect & supine abdominal X-ray (first-line)

• SBO: central dilated loops, valvulae conniventes (plicae) crossing the full width of the lumen; multiple air-fluid levels in a step-ladder ("ladder") pattern; ≥ 3 cm dilated jejunum/ileum.
• LBO: peripheral dilated bowel with haustral folds (do NOT cross the full width); colon dilated > 6 cm, caecum > 9–12 cm.
• Sigmoid volvulus: coffee-bean / omega / bent inner-tube sign — a hugely dilated loop arising from the pelvis pointing to the RUQ.
• Caecal volvulus: dilated caecum displaced to the LUQ ("embryo" / comma sign).
• Gallstone ileus: Rigler's triad — SBO + pneumobilia (gas in biliary tree) + an ectopic (often RIF) radio-opaque gallstone.

Sign	Bowel involved	Loops cross full lumen?	Number of loops
Valvulae conniventes	Small bowel (jejunum)	Yes	Many
Haustra	Large bowel	No (partial)	Few
Coffee-bean sign	Sigmoid volvulus	—	Single huge loop

CT abdomen with contrast — investigation of CHOICE

CT is the most useful modality: it confirms obstruction, defines the level and cause, and detects strangulation/ischaemia.

• Transition point (calibre change from dilated to collapsed bowel) localises the block.
• "Small-bowel faeces sign" marks the transition zone.
• Signs of strangulation/ischaemia: bowel-wall thickening, poor/absent mural enhancement, mesenteric oedema/fat stranding, whirl sign (twisted mesentery in volvulus), pneumatosis intestinalis, portal venous gas, free fluid.

High-yield: CECT abdomen is the single best investigation for suspected intestinal obstruction — it answers level, cause, and (critically) whether there is strangulation, which decides surgery.

Others

• Water-soluble contrast (Gastrografin) study: both diagnostic and therapeutic/prognostic in adhesive SBO — contrast reaching the colon within ~24 h predicts non-operative resolution and may itself relieve obstruction.
• Bloods: raised lactate, leukocytosis, electrolytes (K⁺, Cl⁻), urea/creatinine (dehydration); ABG for acidosis.
• Ultrasound: "target sign" / "pseudo-kidney" in intussusception (investigation of choice in children); also used for reduction guidance.

Management

Initial resuscitation — applies to ALL ("Drip and Suck")

1. NBM (nil by mouth).
2. Nasogastric tube decompression (suck) — relieves distension, prevents aspiration.
3. IV fluids (drip) — correct hypovolaemia and electrolytes (replace K⁺ once urine output adequate).
4. Urinary catheter ± CVP to monitor resuscitation; analgesia, antiemetics, correct electrolytes.
5. Broad-spectrum antibiotics if strangulation/perforation suspected or peri-operatively.

Decision flow: Resuscitate → distinguish simple vs strangulated and partial vs complete →

• Simple, partial, adhesive SBO → trial of conservative management 24–48 h (drip & suck + Gastrografin challenge). Most resolve.
• Strangulation / complete obstruction / closed loop / peritonitis / failure of conservative trial / "virgin abdomen" with no clear adhesion cause → surgery.

High-yield: Adhesive SBO without signs of strangulation is the classic indication for non-operative management. Conversely, any feature of strangulation = immediate operation regardless of cause. The first SBO in a patient who has never had surgery warrants a low threshold for CT/laparotomy (likely hernia/tumour/band).

Cause-specific surgical management

• Obstructed/strangulated hernia: urgent surgery — reduce, assess viability, resect non-viable bowel, repair defect.
• Bands/single adhesion: adhesiolysis (laparoscopic or open).
• Sigmoid volvulus (stable, no gangrene): endoscopic (flexible sigmoidoscopic) decompression + flatus tube is first-line; elective sigmoidectomy later as it recurs. Gangrene → emergency resection (Hartmann's).
• Caecal volvulus: right hemicolectomy is definitive (detorsion alone has high recurrence).
• Malignant LBO: resection; left-sided obstruction may need Hartmann's procedure or a self-expanding metallic stent (SEMS) as a "bridge to surgery" or palliation.
• Gallstone ileus: enterolithotomy to remove the impacted stone (commonly at terminal ileum); the cholecystoduodenal fistula is usually dealt with later (or left).
• Intussusception (children): if stable, pneumatic (air) or hydrostatic reduction under imaging is first-line; surgery if reduction fails, peritonitis, or a pathological lead point.
• Bowel viability check (after relief of strangulation): colour, sheen, peristalsis, mesenteric arterial pulsation; if doubtful, wrap in warm saline packs and re-assess after 10 min; resect frankly necrotic bowel.

Functional obstruction

• Paralytic ileus: conservative — correct electrolytes (esp. K⁺), stop opioids/anticholinergics, NG decompression; usually self-limiting.
• Acute colonic pseudo-obstruction (Ogilvie's syndrome): colonic dilatation without mechanical cause, often in sick/elderly/post-op. Treat conservatively; if caecum > 12 cm or failure → IV neostigmine (first-line pharmacological) under cardiac monitoring → colonoscopic decompression → surgery if all fail.

High-yield: Neostigmine is the drug of choice for Ogilvie's syndrome (acute colonic pseudo-obstruction); keep atropine ready for bradycardia.

Complications

• Strangulation → gangrene → perforation → faecal peritonitis (the lethal cascade).
• Hypovolaemic and septic shock, acute kidney injury, electrolyte derangement (hypokalaemia).
• Caecal perforation in closed-loop LBO (Laplace's law — largest diameter, highest wall tension).
• Aspiration pneumonia (from vomiting), short-bowel syndrome after extensive resection.
• Recurrence (adhesions, volvulus), anastomotic leak after emergency resection.

Key differentials

• Paralytic ileus — distension, absent bowel sounds, no colic; post-op/electrolyte/peritonitis.
• Ogilvie's syndrome — massive colonic dilatation, no mechanical block.
• Pseudo-obstruction / toxic megacolon (IBD, C. difficile).
• Acute mesenteric ischaemia — pain out of proportion, metabolic acidosis (can also cause ileus).
• Severe constipation/faecal impaction, gastroparesis, acute pancreatitis (can mimic with ileus).

Differentiator	Mechanical SBO	Paralytic ileus
Pain	Colicky, intermittent	Dull, continuous or absent
Bowel sounds	Hyperactive, tinkling (early)	Absent
X-ray	Multiple air-fluid levels, dilated loops with collapse distally	Gas throughout incl. rectum/colon, uniform
Onset	Often sudden	Post-op, electrolyte, sepsis

Recently asked / exam angle

• Image-based: identify the coffee-bean sign (sigmoid volvulus), step-ladder air-fluid levels (SBO), Rigler's triad (gallstone ileus), target/doughnut sign on USG (intussusception).
• Most common cause MCQs: SBO in adults = adhesions; SBO without previous surgery = hernia; LBO = carcinoma colon; intussusception in infants = ileocolic.
• Investigation of choice = CECT abdomen for level + cause + strangulation; USG for paediatric intussusception.
• Management single-best: neostigmine for Ogilvie's; sigmoidoscopic decompression first for stable sigmoid volvulus; right hemicolectomy for caecal volvulus; enterolithotomy for gallstone ileus.
• Closed-loop / Laplace's law → caecum perforates first; caecal diameter cut-off > 12 cm.
• Electrolyte pattern: hypokalaemic hypochloraemic metabolic alkalosis (proximal); acidosis suggests strangulation.
• Femoral hernia in elderly woman presenting as obstruction — a recurring clinical-vignette favourite.
• Type of bowel from X-ray: valvulae conniventes cross the full lumen (small bowel) vs haustra do not (large bowel).

Rapid revision

1. Most common cause of SBO in adults = postoperative adhesions; without prior surgery = hernia.
2. Most common cause of LBO = colorectal carcinoma; commonest cause of intestinal obstruction in infants = intussusception (ileocolic).
3. Classic tetrad = colicky pain, vomiting, distension, absolute constipation.
4. Strangulation flags: continuous pain, tachycardia, fever, tenderness/guarding, leukocytosis, raised lactate → operate.
5. CECT abdomen = investigation of choice (level + cause + strangulation, transition point, whirl sign).
6. X-ray: SBO → central, valvulae conniventes crossing full lumen, step-ladder levels; LBO → peripheral, haustra, colon > 6 cm.
7. Coffee-bean sign = sigmoid volvulus; Rigler's triad (SBO + pneumobilia + ectopic gallstone) = gallstone ileus.
8. Competent ileocaecal valve → closed-loop LBO; caecum perforates first (Laplace); danger at > 12 cm.
9. Initial management of all = "drip and suck" (NBM, NG decompression, IV fluids, correct K⁺).
10. Adhesive SBO without strangulation → conservative + Gastrografin challenge; contrast in colon by 24 h predicts resolution.
11. Neostigmine = drug of choice for Ogilvie's syndrome; caecal volvulus = right hemicolectomy; stable sigmoid volvulus = endoscopic decompression then elective sigmoidectomy.
12. Proximal SBO → hypokalaemic hypochloraemic metabolic alkalosis; acidosis = think ischaemia.