A 75-year-old male is hospitalized for bloody diarrhea and abdominal pain after meals. Endoscopic work-up and CT scan lead the attending physician to diagnose ischemic colitis at the splenic flexure. Which of the following would most likely predispose this patient to ischemic colitis:

Obstruction of the abdominal aorta following surgery

Hyperreninemic hyperaldosteronism secondary to type II diabetes mellitus

Increased splanchnic blood flow following a large meal

A 32-year-old man comes to the emergency department because of recurrent episodes of vomiting for 1 day. He has had over 15 episodes of bilious vomiting. During this period he has had cramping abdominal pain but has not had a bowel movement or passed flatus. He does not have fever or diarrhea. He was diagnosed with Crohn disease at the age of 28 years which has been well controlled with oral mesalamine. He underwent a partial small bowel resection for midgut volvulus at birth. His other medications include vitamin B12, folic acid, loperamide, ferrous sulfate, and vitamin D3. He appears uncomfortable and his lips are parched. His temperature is 37.1°C (99.3°F), pulse is 103/min, and blood pressure is 104/70 mm Hg. The abdomen is distended, tympanitic, and tender to palpation over the periumbilical area and the right lower quadrant. Rectal examination is unremarkable. A CT scan of the abdomen shows multiple dilated loops of small bowel with a transition zone in the mid to distal ileum. After 24 hours of conservative management with IV fluid resuscitation, nasogastric bowel decompression, promethazine, and analgesia, his condition does not improve and a laparotomy is scheduled. During the laparotomy, two discrete strictures are noted in the mid-ileum, around 20 cm apart. Which of the following is the most appropriate next step in management?

Strictureplasty of individual strictures

Small bowel resection with ileostomy

Abdominal closure and start palliative care

Small bowel resection and primary anastomosis

Four days after undergoing a total abdominal hysterectomy for atypical endometrial hyperplasia, a 59 year-old woman reports abdominal bloating and discomfort. She has also had nausea without vomiting. She has no appetite despite not having eaten since the surgery and drinking only sips of water. Her postoperative pain has been well controlled on a hydromorphone patient-controlled analgesia (PCA) pump. Her foley was removed on the second postoperative day and she is now voiding freely. Although she lays supine in bed for most of the day, she is able to walk around the hospital room with a physical therapist. Her temperature is 36.5°C (97.7°F), pulse is 84/min, respirations are 10/min, and blood pressure is 132/92 mm Hg. She is 175 cm (5 ft 9 in) tall and weighs 115 kg (253 lb); BMI is 37.55 kg/m2. Examination shows a mildly distended, tympanic abdomen; bowel sounds are absent. Laboratory studies are within normal limits. An x-ray of the abdomen shows uniform distribution of gas in the small bowel, colon, and rectum without air-fluid levels. Which of the following is the most appropriate next step in the management of this patient?

Begin total parenteral nutrition

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

"Can you tell me more about the symptoms you have been experiencing?"

"Does the diarrhea typically precede the constipation, or vice-versa?"

"Is the diarrhea foul-smelling?"

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

"Are the symptoms worse in the morning or at night?"

Ileus and bowel dysfunction for USMLE Step 3: High-Yield Surgery Lessons

Ileus & SBO - The Great Gut Slowdown

Ileus: Functional, non-mechanical obstruction. Uniformly dilated bowel loops. Common causes: post-op state, opioids, hypokalemia, sepsis.
Small Bowel Obstruction (SBO): True mechanical blockage. Key finding: transition point with dilated proximal bowel and collapsed distal bowel. Common causes: Adhesions (>75%), hernias, tumors.

⭐ The most common cause of SBO is post-surgical adhesions. In a "virgin" abdomen (no prior surgery), incarcerated hernias are a primary suspect.

Pathophysiology - Guts on Strike

Post-surgical gut paralysis (ileus) results from a coordinated inflammatory and neurogenic response.

Neurogenic Phase (Immediate):
- Surgical stress activates splanchnic nerves, leading to a surge in sympathetic tone (norepinephrine).
- Inhibits parasympathetic (vagal) activity, silencing pro-kinetic pathways.
Inflammatory Phase (Delayed):
- Gut handling triggers resident macrophage activation in the muscularis externa.
- Release of inflammatory mediators (e.g., IL-1α, IL-6, TNF-α) recruits more leukocytes.
- This inflammatory soup suppresses smooth muscle contractility.

Abdominal X-ray: Dilated bowel loops in paralytic ileus

⭐ Ileus is physiologic for 2-3 days post-op. If it persists beyond 3-5 days (prolonged ileus), it must be distinguished from mechanical obstruction, often requiring CT imaging.

Diagnosis & Workup - Deciphering the Silence

Clinical Evaluation:
- History: Recent surgery, medications (opioids), electrolyte imbalance.
- Physical Exam: Abdominal distension, minimal tenderness, absent/hypoactive bowel sounds.
Imaging Studies:
- Abdominal X-ray (AXR): First-line test. Shows generalized, uniform dilation of both small and large bowel; no transition point.
- CT Scan: More specific. Confirms ileus, rules out mechanical obstruction, and can identify underlying causes (e.g., abscess).

Abdominal X-ray: Paralytic ileus with bowel dilation

⭐ On imaging, paralytic ileus is distinguished from SBO by gas and dilation throughout both the small and large bowel, whereas SBO typically shows a clear transition point with distal bowel collapse.

Management - Getting Things Moving

Conservative First: NPO/clears, IV fluids, correct electrolytes (K⁺, Mg²⁺), early & frequent ambulation.
Decompression: Nasogastric (NG) tube if significant vomiting or distention.
Remove Obstacles: Minimize opioids (use multimodal analgesia), treat underlying causes.
Pharmacologic Aids:
- Alvimopan: Peripherally-acting µ-opioid antagonist for postoperative ileus after bowel resection.
- Chewing gum can act as "sham feeding" to stimulate the vagus nerve.

⭐ Alvimopan is for short-term, inpatient use only (max 7 days or 15 doses) due to an increased risk of myocardial infarction with long-term use.

Abdominal X-ray: Postoperative ileus with dilated bowel

High‑Yield Points - ⚡ Biggest Takeaways

Postoperative ileus is a functional, non-mechanical bowel obstruction from inflammatory mediators and ↑ sympathetic tone.

Presents with absent bowel sounds, nausea, vomiting, and failure to pass flatus or stool.

Physiologic ileus typically resolves within 72 hours; a longer duration is considered prolonged ileus.

Opioid use is the most significant risk factor; also check for hypokalemia.

Management is supportive: NPO, IV fluids, and minimizing opioids.

Differentiate from SBO via X-ray: ileus shows diffusely dilated bowel loops, while SBO has a clear transition point.

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