bowel obstruction

**DEFINITION / TYPES** - Mechanical obstruction: a physical blockage, either partial or complete. - Functional obstruction (ileus, pseudo-obstruction): impaired peristalsis with no physical blockage. - Simple obstruction: the lumen is blocked but blood supply is intact. - Closed-loop obstruction: both ends of a bowel segment are occluded (e.g., volvulus, or a loop trapped under an adhesive band). It carries a high risk of ischemia and perforation. - Strangulated obstruction: vascular compromise causes ischemia and necrosis. This is a surgical emergency.

**ETIOLOGY** - Small bowel obstruction (SBO): - Adhesions from prior abdominal or pelvic surgery (~60-75%, the #1 cause in developed countries). - Hernias (incarcerated inguinal, femoral, or incisional; #1 cause worldwide and in patients with no prior surgery). - Neoplasms or metastases. - Crohn disease strictures. - Intussusception (a classic pediatric cause; in adults it suggests a lead point such as a tumor). - Gallstone ileus (Rigler triad: SBO, pneumobilia, ectopic gallstone), caused by a cholecystoenteric fistula with stone impaction at the ileocecal valve. - Volvulus, foreign body, and bezoar. - Large bowel obstruction (LBO): - Colorectal cancer (#1 cause, usually in the sigmoid or left colon). - Sigmoid volvulus (elderly, institutionalized, chronic constipation; "coffee bean" sign, with the bowel loop pointing toward the RUQ). - Cecal volvulus (younger patients; coffee bean pointing toward the LUQ). - Diverticular stricture. - Pediatric causes: - Meconium ileus (cystic fibrosis). - Intestinal atresia. - Malrotation with midgut volvulus (bilious emesis in a neonate). - Pyloric stenosis (gastric outlet). - Hirschsprung disease. - Intussusception (6-36 months; "currant jelly" stool). - Functional causes: - Postoperative ileus. - Electrolyte disturbances (hypokalemia). - Opioids and anticholinergics. - Ogilvie syndrome (acute colonic pseudo-obstruction in hospitalized or critically ill patients).

**PATHOPHYSIOLOGY** - Fluid, gas, and secretions accumulate proximal to the obstruction. Swallowed air and bacterial fermentation worsen distension. - Bowel wall edema and increased intraluminal pressure impair venous return, then arterial inflow, which causes ischemia and necrosis. - Third-spacing and vomiting cause hypovolemia, hypochloremic metabolic alkalosis, and hypokalemia. - Bacterial translocation can cause sepsis. - In LBO with a competent ileocecal valve, a closed loop forms, and the cecum is at greatest risk of perforation (Laplace law; risk is highest at a diameter >12 cm).

**CLINICAL FEATURES** - SBO: colicky periumbilical pain, early and bilious vomiting, distension, and obstipation (later if the obstruction is proximal or partial). - LBO: gradual onset, prominent distension, late vomiting (feculent), and early obstipation and constipation. - Exam: distension, high-pitched "tinkling" bowel sounds early (diminished or absent late), tympany, and hernias (always examine the groin and surgical scars). - Red flags for strangulation or perforation: constant (non-colicky) severe pain, fever, tachycardia, peritonitis, leukocytosis, elevated lactate, and metabolic acidosis.

**DIAGNOSIS** - CT abdomen/pelvis with IV contrast is the best test. It shows a transition point, proximal dilation (small bowel >3 cm), and distal collapse, and it can identify the cause and signs of ischemia (wall thickening, pneumatosis, mesenteric edema, reduced enhancement). - Plain abdominal X-ray (often the initial study): - SBO: dilated loops centrally, "stepladder" air-fluid levels, valvulae conniventes crossing the whole lumen, and a paucity of colonic gas. - LBO: peripheral dilated colon with haustra that do not cross the entire lumen. - Free air under the diaphragm indicates perforation. - Labs: BMP (hypokalemia, contraction alkalosis, AKI), CBC, and lactate. - Water-soluble contrast (Gastrografin) is both diagnostic and therapeutic in adhesive SBO. - Sigmoid volvulus: "coffee bean" sign (X-ray) and "bird's beak" (contrast enema). Pediatric intussusception: "target" or "doughnut" sign on ultrasound.

**MANAGEMENT** - Initial care for all patients: NPO, IV fluids and electrolyte repletion, nasogastric decompression, analgesia and antiemetics, and a Foley catheter to monitor urine output. - Partial or uncomplicated adhesive SBO: conservative management (bowel rest and NG tube), which resolves in most cases. - Emergent surgery is indicated for: - Complete obstruction with signs of strangulation, ischemia, or peritonitis. - Closed-loop obstruction. - Perforation. - Incarcerated hernia. - Failure of conservative therapy (generally 48-72 hours). - Sigmoid volvulus: sigmoidoscopic detorsion if there is no ischemia, followed by elective sigmoid resection. Go directly to surgery if there is ischemia or peritonitis. - Cecal volvulus: surgery (right hemicolectomy). - LBO from cancer: colonic stent as a bridge to surgery, or diversion/resection (Hartmann procedure). - Ogilvie syndrome: supportive care and correction of underlying causes. If cecal diameter is >10-12 cm or the patient is not improving, give neostigmine (contraindicated in mechanical obstruction, bradycardia, and bronchospasm) or perform colonoscopic decompression. - Pediatric intussusception: air or contrast enema (diagnostic and therapeutic); surgery if there is peritonitis or the enema fails.

**HIGH-YIELD BOARD PEARLS** - Previous abdominal surgery plus vomiting and distension = adhesive SBO. - No prior surgery plus SBO = look for a hernia first. - An elderly patient with a "coffee bean" sign = sigmoid volvulus. - SBO plus air in the biliary tree in an elderly woman = gallstone ileus. - Ileus vs obstruction: ileus shows diffuse gas through the small bowel and colon, with absent bowel sounds and no transition point. - Complications: strangulation, perforation, sepsis, and short bowel syndrome after resection. - Persistent vomiting causes hypochloremic, hypokalemic metabolic alkalosis, and the same pattern occurs with gastric outlet obstruction.