Small bowel obstruction

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Etiology & Pathophysiology - Getting All Tied Up

  • Most Common Causes (📌 ABC):
    • Adhesions (post-operative, ~75%)
    • Bulge (incarcerated hernias)
    • Cancer (tumors, intrinsic or extrinsic)
  • Pathophysiology Cascade:
    • Obstruction → Proximal bowel dilation (gas/fluid) → ↑ Intraluminal pressure.
    • Bowel wall edema & third-spacing → Hypovolemia & electrolyte shifts.
    • Venous & arterial compromise → Ischemia, necrosis, perforation.

Small Bowel Obstruction: Causes

Strangulation is a surgical emergency, marked by fever, tachycardia, leukocytosis, and localized pain. It implies compromised blood flow requiring immediate intervention to prevent bowel necrosis.

Clinical Presentation - The Gut's Cry for Help

  • Cardinal Symptoms (📌 CAVO):
    • Colicky abdominal pain: Initially periumbilical & crampy; becomes constant & severe with strangulation.
    • Abdominal distension: More pronounced in distal SBO.
    • Vomiting: Early, bilious (proximal SBO) vs. late, feculent (distal SBO).
    • Obstipation: Failure to pass stool or flatus; a late finding indicating complete obstruction.
  • Physical Exam Findings:
    • Bowel sounds: Early high-pitched "tinkles" → Late hypoactive/absent sounds.
    • ⚠️ Peritoneal signs (e.g., rebound tenderness, guarding) suggest strangulation or perforation.

⭐ A patient with partial SBO may still pass flatus or have diarrhea.

Diagnosis - Peeking Inside the Pipes

  • Labs: CBC, BMP, lactate, and type & screen. Look for leukocytosis, electrolyte abnormalities, and signs of ischemia (↑ lactate).
  • Abdominal X-ray (AXR): Initial imaging.
    • Dilated small bowel loops (>3 cm).
    • Multiple air-fluid levels on upright film.
    • Paucity of gas in the colon.

Upright Abdominal X-ray: Small Bowel Obstruction

  • CT Scan (Abdomen/Pelvis with IV contrast): Gold standard for diagnosis.
    • Confirms diagnosis, identifies location, severity, and etiology (e.g., hernia, mass).
    • Determines presence of complications (ischemia, perforation).

Exam Favorite: The most important finding on CT is the transition point-a discrete location where the bowel caliber changes from dilated proximal loops to collapsed distal loops, pinpointing the obstruction site.

Management - Untangling the Knot

  • Initial Stabilization (Conservative): The cornerstone for all SBO patients.

    • NPO (Nil Per Os): Bowel rest is critical.
    • IV Fluids: Aggressive resuscitation with isotonic crystalloids (Lactated Ringer's or Normal Saline) to correct dehydration.
    • Nasogastric (NG) Tube: Decompresses the stomach and proximal bowel, reducing distention and vomiting.
    • Monitor urine output (goal > 0.5 mL/kg/hr) and electrolytes.
  • Definitive Management: The decision to operate hinges on the presence of complications.

⭐ In a "virgin" abdomen (no prior surgery), a hernia is the most likely cause of SBO. Always perform a thorough physical exam to check for incarcerated hernias, as this is a surgical emergency.

High‑Yield Points - ⚡ Biggest Takeaways

  • Adhesions from prior surgery are the #1 cause of SBO.
  • Cardinal features are colicky abdominal pain, vomiting, abdominal distension, and obstipation.
  • Exam reveals high-pitched, tinkling bowel sounds early on, which later become hypoactive.
  • Abdominal X-ray shows dilated small bowel loops (>'''3 cm''') with air-fluid levels.
  • CT scan is the diagnostic standard, confirming the diagnosis and identifying the transition point.
  • Initial management is conservative: NPO, IV fluids, and NG tube decompression.
  • Peritoneal signs, acidosis, or failure to resolve indicate strangulation and require urgent surgery.
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Practice Questions: Small bowel obstruction

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A 69-year-old male presents to the Emergency Department with bilious vomiting that started within the past 24 hours. His medical history is significant for hypertension, hyperlipidemia, and a myocardial infarction six months ago. His past surgical history is significant for a laparotomy 20 years ago for a perforated diverticulum. Most recently he had some dental work done and has been on narcotic pain medicine for the past week. He reports constipation and obstipation. He is afebrile with a blood pressure of 146/92 mm Hg and a heart rate of 116/min. His abdominal exam reveals multiple well-healed scars with distension but no tenderness. An abdominal/pelvic CT scan reveals dilated small bowel with a transition point to normal caliber bowel distally. When did the cause of his pathology commence?

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Flashcards: Small bowel obstruction

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Malrotation can lead to _____ and duodenal obstruction

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Malrotation can lead to _____ and duodenal obstruction

volvulus

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