Bowel Obstruction: Nursing Study Guide

Bowel obstruction is a high-yield GI topic on nursing exams. This guide reviews the difference between mechanical and non-mechanical obstruction, how small and large bowel obstructions present differently, the major complications to watch for, and the priority nursing interventions.

What Is Bowel Obstruction?

• A bowel obstruction is a blockage that prevents the normal passage of intestinal contents.
• It is classified as:
  • Mechanical obstruction — a physical blockage.
  • Non-mechanical obstruction (paralytic ileus) — functional paralysis of the bowel.

Causes of Mechanical Obstruction

• Intraluminal (inside the bowel lumen): gallstones, bezoars, foreign bodies.
• Mural (within the bowel wall): colorectal cancer, Crohn's strictures.
• Extraluminal (outside the bowel wall): adhesions, hernias, volvulus.

Key points:

• Adhesions are the most common cause of small bowel obstruction (SBO).
• Colorectal cancer is the most common cause of large bowel obstruction (LBO).

Non-Mechanical Obstruction (Paralytic Ileus)

• A functional obstruction in which peristalsis stops without a physical blockage.
• Common causes: abdominal surgery, opioids, hypokalemia, peritonitis, sepsis.
• Bowel sounds are absent or hypoactive; pain is constant and dull rather than cramping.

Small vs Large Bowel Obstruction

• Most common cause: SBO — adhesions; LBO — colorectal cancer.
• Vomiting: SBO — early, profuse, bilious; LBO — late, may be feculent.
• Electrolytes: SBO — hypokalemia, metabolic alkalosis; LBO — minimal early.
• Primary complication: SBO — strangulation; LBO — perforation (cecal rupture).
• Abdominal distension: SBO — mild to moderate; LBO — severe.

Clinical Presentation and Complications

Small Bowel Obstruction

• Cramping or colicky abdominal pain.
• High-pitched tinkling bowel sounds.
• Early bilious vomiting.
• Hypokalemia and metabolic alkalosis from vomiting.
• Main complication is strangulation — signs include fever, tachycardia, and constant pain.

Large Bowel Obstruction

• Constant lower abdominal pain, severe distension, and early constipation.
• Main complication is perforation — the cecum ruptures under pressure.
• Signs of perforation: sudden severe pain and a rigid, board-like abdomen.

Paralytic Ileus

• Constant dull pain, absent bowel sounds, and diffuse distension.
• Patient may pass small amounts of gas or stool early.

Diagnostic Tests

• Abdominal X-ray: dilated bowel loops with air-fluid levels.
• CT scan: gold standard for identifying the cause and level of obstruction.
• SBO: dilated small bowel loops with a step-ladder pattern.
• LBO: dilated colon proximal to the obstruction.
• Paralytic ileus: diffuse dilation of both small and large bowel without a transition point.

Management

• First priority: nasogastric (NG) tube decompression and IV fluid resuscitation.
• Correct hypokalemia and metabolic alkalosis in SBO before surgery.
• Surgery is needed for complete obstruction, strangulation, or perforation.
• Paralytic ileus: stop opioids, correct electrolytes, and encourage ambulation.

Nursing Assessment

• Assess pain pattern: cramping (mechanical) vs constant (ileus or strangulation).
• Auscultate bowel sounds: high-pitched tinkling (early mechanical) vs absent (ileus or late obstruction).
• Monitor for strangulation: fever, tachycardia, constant pain.
• Monitor for perforation: sudden severe pain, rigid abdomen.
• Monitor electrolytes — hypokalemia and metabolic alkalosis are common in SBO.

Nursing Interventions

• Insert an NG tube and connect to low intermittent suction.
• Maintain NPO status and provide frequent oral care.
• Administer IV fluids and replace electrolytes as ordered.
• Do not give laxatives or enemas if obstruction is suspected.
• After surgery, monitor the incision for redness, drainage, or dehiscence.
• Monitor for return of bowel function (passing flatus or stool) before advancing the diet.

Patient Teaching

• Report worsening abdominal pain, vomiting, or inability to pass gas or stool.
• Follow NPO status and advance diet slowly as directed.

Common Exam Traps

• Adhesions → most SBOs; colorectal cancer → most LBOs.
• Hypokalemia + metabolic alkalosis = classic SBO finding.
• Strangulation (fever, tachycardia, constant pain) = main SBO complication.
• Perforation (sudden severe pain, rigid abdomen) = main LBO complication.
• High-pitched tinkling bowel sounds = mechanical obstruction.
• Absent bowel sounds = paralytic ileus or late mechanical obstruction.
• First priority is NG tube and IV fluids, not surgery.
• Never give laxatives or enemas if obstruction is suspected.

Key takeaways

• Bowel obstruction is either mechanical (physical blockage) or non-mechanical (paralytic ileus).
• SBO: early bilious vomiting, hypokalemia, metabolic alkalosis — watch for strangulation.
• LBO: severe distension, late vomiting, early constipation — watch for perforation.
• First priorities are NG decompression and IV fluid resuscitation; surgery is reserved for complete obstruction, strangulation, or perforation.
• Treat paralytic ileus by stopping opioids, correcting electrolytes, and promoting ambulation.
• Never give laxatives or enemas when obstruction is suspected.