Clinical meaning
Bowel obstruction is classified as mechanical (physical blockage) or functional (paralytic ileus from impaired peristalsis). Small bowel obstruction (SBO) accounts for 80% of cases, most commonly from postoperative adhesions. Large bowel obstruction (LBO) is most commonly caused by colorectal cancer. As the bowel dilates proximal to the obstruction, massive third-spacing of fluid occurs (up to 8L/day can sequester), causing hypovolemia, electrolyte derangements (hypokalemia, metabolic alkalosis from vomiting), and risk of bowel ischemia. The nurse manages fluid resuscitation, NG decompression, electrolyte correction, and monitors for surgical indications.
Exam relevance
Risk factors: - Prior abdominal/pelvic surgery (adhesions) - Incarcerated hernia - Colorectal malignancy - Crohn's disease with stricture - Volvulus (sigmoid most common in elderly) - Diverticular disease - Gallstone ileus - Radiation enteritis
Diagnostics: - Interpret abdominal X-ray: dilated loops, air-fluid levels, absence of distal gas - Evaluate CT abdomen with IV contrast: transition point, closed-loop obstruction, bowel wall enhancement - Monitor electrolytes: hypokalemia from vomiting, metabolic alkalosis - Assess lactate level: elevated suggests bowel ischemia - Monitor CBC: leukocytosis suggests strangulation or perforation - Track NG tube output volume and character