Ch22: Intestinal Obstruction（肠梗阻）

Preparatory Mindset

Intestinal obstruction = interference with the normal movement of bowel contents — a common surgical emergency. The lecture (Dr. Pan, 9.3KB) covers concept, classification, pathophysiology, diagnosis, treatment, and examples; the mortality improvement (1932: 40% simple/52% strangulated → 1986: 3%/<8%) shows why early diagnosis matters.

Exam mindset: mechanical vs adynamic vs vascular obstruction; simple vs strangulated (the critical distinction — strangulation = emergency surgery); the classic air-fluid levels on X-ray; and the general treatment (NG decompression + fluids + surgery for strangulation/complete mechanical). Adhesions & hernias = 70% of mechanical obstruction.

Core Concepts

1. Classification (MUST KNOW)

- Causes: hernias & adhesions ~70%, tumors ~15%, others (intussusception, volvulus, obturation/fecal impaction, stricture, gallstone ileus, foreign body)

- Paralytic ileus (麻痹性): post-op, peritonitis, sepsis, hypokalemia, drugs (opioids) — most common - Spastic (痉挛性): rare (lead poisoning, porphyria)

- Small vs large bowel obstruction - Simple (单纯性) vs strangulated (绞窄性) - Complete vs partial; acute vs chronic - Closed-loop obstruction (both ends blocked — high strangulation risk: volvulus, hernia neck)

• Mechanical obstruction (机械性): physical blockage
• Adynamic obstruction (动力性): no physical block — bowel fails to contract
• Vascular obstruction (血运性): mesenteric ischemia/infarction — SMA embolism/thrombosis → bowel death (see also Ch18 mesenteric ischemia)
• Other classifications:

2. Pathophysiology (MUST KNOW)

• Proximal to the obstruction: accumulation of gas (80% swallowed air) & fluid (secretions) → distension, ↑ intraluminal pressure, ↓ absorption, ↑ secretion → massive fluid sequestration ("third-space") → hypovolemia, electrolyte imbalance, dehydration
• Strangulation: blood supply compromised (twisted/closed loop, hernia neck) → ischemia → necrosis → perforation → peritonitis, sepsis, shock
• Systemic: hypovolemia, electrolyte disturbance (K+ loss), metabolic acidosis (strangulation), respiratory compromise (distension splints the diaphragm), bacterial translocation
• Key concept: the "vicious cycle" — distension → more secretion → more distension

3. Clinical features (MUST KNOW)

- Constant severe pain (loses colicky character) - Tenderness, guarding, rigidity, rebound (peritonism) - Fever, tachycardia, hypotension (shock), leukocytosis, metabolic acidosis, ↑ lactate - Bloody stools/NG aspirate; palpable tender mass (closed loop) - Absent bowel sounds (late)

• Cardinal symptoms: colicky abdominal pain + vomiting + abdominal distension + absolute constipation (no flatus)
• Small bowel obstruction (SBO): rapid onset, frequent vomiting (bilious) early, central colicky pain, distension moderate; air-fluid levels ("ladder pattern") on erect X-ray
• Large bowel obstruction (LBO): slower onset, distension prominent, vomiting late/fecal, constipation; colorectal cancer most common cause; X-ray shows peripheral haustra; cecal distension (>9 cm) = risk of perforation
• Strangulation features (MUST KNOW — "red flags"):
• Physical: distension, visible peristalsis, hernial orifices (inguinal/femoral — always examine!), scars (adhesions), abdominal mass (tumor, intussusception), rectal exam (mass, blood, fecal impaction)

4. Investigations (MUST KNOW)

- Abdominal X-ray (erect + supine): dilated loops, air-fluid levels ("ladder" — SBO; "coffee bean" — sigmoid volvulus; "bird's beak" — volvulus), absent gas in the colon (SBO), no free air; small bowel = central valvulae conniventes; large bowel = peripheral haustra - CT abdomen with contrast: the definitive study — identifies the level, cause (adhesions, tumor, hernia), strangulation (bowel wall thickening, pneumatosis, poor enhancement, free fluid/air), closed loop, and complications - Water-soluble contrast studies (Gastrografin) — differentiate partial vs complete SBO & may be therapeutic (postop adhesions) - Water-soluble contrast enema for LBO (obstruction vs pseudo-obstruction)

• Bloods: CBC, electrolytes, renal, lactate, ABG, LFTs, amylase; cross-match
• Imaging:
• Colonoscopy — therapeutic/diagnostic for LBO (stenting)

5. Treatment (MUST KNOW)

1. NPO (nil by mouth) 2. NG tube decompression (relieves vomiting & distension) 3. IV fluids & electrolytes (correct hypovolemia & K+) 4. Urinary catheter (monitor output) 5. Analgesia, antiemetics (after assessment) 6. Broad-spectrum antibiotics (if strangulation suspected/peritonitis)

- Strangulated / peritonitis / closed loop / complete mechanical / failed non-operative → URGENT/emergency surgery - Partial obstruction / early adhesive SBO (no strangulation): trial of non-operative management (NG, fluids, water-soluble contrast) 24-48 h; operate if no resolution - Paralytic ileus: treat the cause (electrolytes, stop opioids, mobilize); NG/fluids

- Adhesiolysis (divide adhesions) - Hernia reduction + repair (if hernia is the cause) - Resection & anastomosis for strangulated/necrotic bowel, tumor, intussusception - Tumor: resection ± stoma (LBO — Hartmann's if unprepared); colonic stent as bridge/palliation - Volvulus: sigmoid — endoscopic decompression first then elective resection; cecal — resection - Stoma creation if peritonitis/unstable/malignant - Gallstone ileus: enterolithotomy (remove the stone; ± cholecystectomy/fistula repair) - Closed-loop/strangulated: emergency surgery, resect non-viable bowel

• General (non-operative) measures — ALL patients:
• Decision: operate vs non-operative
• Surgical options:
• Post-op: ICU if needed, monitor for complications (anastomotic leak, recurrent obstruction, short bowel if massive resection, sepsis)

6. Specific causes (MUST KNOW)

• Adhesive SBO: most common cause of SBO (prior surgery); usually partial — trial of NOM
• Hernias: always examine the hernial orifices (strangulated hernia → emergency)
• Intussusception (肠套叠): children <2 yrs — currant-jelly stool, intermittent colicky pain, sausage-shaped mass; US ("target sign"); air/contrast enema reduction (or surgery)
• Volvulus (肠扭转): sigmoid (elderly — coffee-bean sign) & cecal (young); closed loop → strangulation risk → urgent decompression/resection
• Colorectal cancer: most common cause of LBO — stent then elective resection or emergency resection
• Pseudo-obstruction (Ogilvie's): massive colonic distension without mechanical block (critically ill, post-op) — treat cause, neostigmine, colonoscopic decompression; cecal >12 cm = decompress
• Paralytic ileus: post-op day 2-3 — NPO, fluids, mobilize; resolves spontaneously

High-Yield Points

• Cardinal: colicky pain + vomiting + distension + constipation (no flatus)
• Mechanical (70% adhesions+hernias) vs adynamic (ileus) vs vascular (ischemia)
• Strangulation red flags: constant pain, peritonism, fever, tachycardia, acidosis, lactate ↑ → URGENT surgery
• X-ray: air-fluid levels ("ladder" SBO, "coffee bean" sigmoid volvulus); CT = definitive (strangulation signs)
• Treatment: NPO + NG + IV fluids + electrolytes + monitoring; surgery for strangulation/complete/failed NOM
• SBO (adhesive) partial: trial of NOM 24-48 h; water-soluble contrast helps
• Always examine hernial orifices in obstruction!
• Intussusception (child): currant-jelly stool, target sign, enema reduction
• LBO most common cause = colorectal cancer; cecal >9-12 cm = perforation risk
• Ogilvie's = pseudo-obstruction (no mechanical block) — neostigmine/decompression

Topic Summary

Intestinal obstruction: mechanical (adhesions & hernias 70%, tumors 15%), adynamic (paralytic ileus), vascular (mesenteric ischemia). Pathophysiology: gas (swallowed air) + fluid accumulation → distension → third-space hypovolemia → strangulation (ischemia/perforation). Symptoms: colicky pain + vomiting + distension + constipation; strangulation = constant pain, peritonism, fever, acidosis → emergency surgery. Diagnosis: X-ray (air-fluid levels/ladder; coffee-bean sigmoid), CT definitive. Treatment: NPO, NG decompression, IV fluids/electrolytes, monitoring; non-operative trial for partial/adhesive SBO; surgery for strangulation, complete mechanical, failed NOM (adhesiolysis, hernia repair, resection, stoma, stenting). Specifics: intussusception (enema reduction), volvulus (decompress then resect), colorectal cancer (LBO cause), Ogilvie's pseudo-obstruction (neostigmine). Paralytic ileus: treat the cause.