Lecture Notes: Bowel Obstruction

Introduction

• Discussing bowel obstruction as part of clinical medicine.
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Types of Bowel Obstructions

Mechanical Obstruction

• Definition: A physical blockage within the lumen preventing movement of intestinal contents.
• Characteristics:
  • No problem with motility; smooth muscle function is intact.
  • Leads to increased motility initially, then decreases in late stages.
  • Radiographically shows a transition point with proximal distension and distal decompression.

Functional Obstruction

• Definition: No physical blockage; problem lies in motility.
• Characteristics:
  • Smooth muscle cannot contract effectively to induce peristalsis.
  • Distended bowel loops throughout with no transition point.

Presentation and Symptoms

• Common symptoms include cramping abdominal pain, distension, vomiting, and obstipation.
• Radiographic indicators differentiate between mechanical and functional obstructions.

Causes Based on Bowel Area

Small Bowel Obstruction (SBO)

• Common Causes:
  1. Adhesions: From previous abdominal surgeries.
  2. Hernias: Inguinal or femoral, leading to incarceration or strangulation.
  3. Intussusception: Often in children; particularly at the ileocecal junction.

Large Bowel Obstruction (LBO)

• Common Causes:
  • Tumors: Intrinsic like colorectal cancer or extrinsic compression.
  • Volvulus: Twisting of the bowel, common in adults with chronic constipation.

Functional Obstructions

• Small Bowel:
  • Paralytic Ileus: Dilated loops, usually due to peritonitis, post-op states, low potassium, or opiate use.
• Large Bowel:
  • Colonic Pseudo-Obstruction or Ogilvie's Syndrome: Dilated colon, often due to similar causes as paralytic ileus.

Complications

Hypovolemia

• Causes: Vomiting leading to water and sodium loss, bowel wall distension, decreased absorption and increased secretion.
• Symptoms: Decreased skin turgor, tachycardia, dry mucous membranes, hypotension.

Electrolyte Imbalance

• Hypokalemia: Due to potassium loss.
• Metabolic Alkalosis: Due to proton loss.

Bowel Ischemia and Perforation

• Ischemia: Due to high intraluminal pressure compressing arteries, leading to necrosis.
• Perforation: Risk increases with continued ischemia; can result in sepsis and pneumoperitoneum.

Diagnosis

• Initial Assessment: Rule out perforation using abdominal X-ray to check for air under the diaphragm.
• Mechanical Obstruction: CT abdomen/pelvis to identify transition points.
• Functional Obstruction: Lack of transition points, absent bowel sounds.
• Specific Signs:
  • Small bowel: Dilated loops >3cm.
  • Large bowel: Dilated colon >6cm, cecum >9cm.

Treatment

Mechanical Obstructions

• Supportive Care: Decompress bowel with an NG tube, keep patient NPO, IV fluid replacement.
• Surgical Intervention: Required for complete or closed-loop obstructions, especially with ischemia or perforation.

Functional Obstructions

• General Management: Decompression, IV fluids, maintain NPO status.
• Specific Treatments:
  • Rectal tube for large bowel decompression.
  • Laxatives and neostigmine for improving motility in Ogilvie's syndrome.
• Surgical: Necessary in cases of severe ischemia or perforation.

These notes cover the pathology, diagnostic strategies, and management of bowel obstructions, distinguishing between mechanical and functional causes and their respective treatments.