A 76-year-old female is brought to the emergency department after being found unresponsive in her room at her nursing facility. Past medical history is significant for Alzheimer's disease, hypertension, and diabetes. Surgical history is notable for an open cholecystectomy at age 38 and multiple cesarean sections. On arrival, she is non-responsive but breathing by herself, and her vital signs are T 102.9 F, HR 123 bpm, BP 95/64, RR 26/min, and SaO2 97% on 6L nasal cannula. On physical exam the patient has marked abdominal distension and is tympanic to percussion. Laboratory studies are notable for a lactic acidosis. An upright abdominal radiograph and CT abdomen/pelvis with contrast are shown in Figures A and B respectively. She is started on IV fluids and a nasogastric tube is placed to suction which returns green bilious fluid. Repeat vitals 1 hour later are T 101F, HR 140 bpm, BP 75/44, RR 30/min, and SaO2 is 100% on the ventilator after she is intubated for airway concerns. What is the next best step in management?

Immediate laparotomy and surgical management

Sigmoidoscopy, attempted derotation and rectal tube placement

Continue IV fluid hydration, nasogastric suction, NPO

Therapy with levofloxacin and metronidazole

A 54-year-old man comes to the physician because of diarrhea that has become progressively worse over the past 4 months. He currently has 4–6 episodes of foul-smelling stools per day. Over the past 3 months, he has had fatigue and a 5-kg (11-lb) weight loss. He returned from Bangladesh 6 months ago after a year-long business assignment. He has osteoarthritis and hypertension. Current medications include amlodipine and naproxen. He appears pale and malnourished. His temperature is 37.3°C (99.1°F), pulse is 76/min, and blood pressure is 140/86 mm Hg. Examination shows pale conjunctivae and dry mucous membranes. Angular stomatitis and glossitis are present. The abdomen is distended but soft and nontender. Rectal examination shows no abnormalities. Laboratory studies show: Hemoglobin 8.9 g/dL Leukocyte count 4100/mm3 Platelet count 160,000/mm3 Mean corpuscular volume 110 μm3 Serum Na+ 133 mEq/L Cl- 98 mEq/l K+ 3.3 mEq/L Creatinine 1.1 mg/dL IgA 250 mg/dL Anti-tissue transglutaminase, IgA negative Stool culture and studies for ova and parasites are negative. Test of the stool for occult blood is negative. Fecal fat content is 22 g/day (N < 7). Fecal lactoferrin is negative and elastase is within normal limits. Which of the following is the most appropriate next step in diagnosis?

PAS-stained biopsy of small bowel

IgG against deamidated gliadin peptide

A 75-year-old man is brought to the emergency department after 2 days of severe diffuse abdominal pain, nausea, vomiting, and lack of bowel movements, which has led him to stop eating. He has a history of type-2 diabetes mellitus, hypertension, and chronic obstructive pulmonary disease. Upon admission, his vital signs are within normal limits and physical examination shows diffuse abdominal tenderness, distention, lack of bowel sounds, and an empty rectal ampulla. After initial fluid therapy and correction of moderate hypokalemia, the patient's condition shows mild improvement. His abdominal plain film is taken and shown. Which of the following is the most appropriate concomitant approach?

Initiate pain management with morphine

Initiate intravenous metoclopramide

A 55-year-old woman comes to the emergency department because of a 24-hour history of severe lower abdominal pain. She has had two episodes of nonbloody vomiting today and has been unable to keep down food or fluids. She has not had a bowel movement since the day before. She has hypertension, hyperlipidemia, and osteoarthritis. She had a cholecystectomy 5 years ago. She has smoked one pack of cigarettes daily for the last 20 years. Current medications include chlorthalidone, atorvastatin, and naproxen. Her temperature is 38.8°C (101.8°F), pulse is 102/min, respirations are 20/min, and blood pressure is 118/78 mm Hg. She is 1.68 m (5 ft 6 in) tall and weighs 94.3 kg (207.9 lbs); BMI is 33.4 kg/m2. Abdominal examination shows a soft abdomen with hypoactive bowel sounds. There is moderate left lower quadrant tenderness. A tender mass is palpable on digital rectal examination. There is no guarding or rebound tenderness. Laboratory studies show: Leukocyte count 17,000/mm3 Hemoglobin 13.3 g/dl Hematocrit 40% Platelet count 188,000/mm3 Serum Na+ 138 mEq/L K+ 4.1 mEq/L Cl- 101 mEq/L HCO3- 22 mEq/L Urea Nitrogen 18.1 mg/dl Creatinine 1.1 mg/dl Which of the following is most appropriate to confirm the diagnosis?

CT scan of the abdomen with contrast

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

Small bowel obstruction for USMLE Step 2 CK: High-Yield Surgery Lessons

Etiology & Pathophysiology - Getting All Tied Up

Most Common Causes (📌 ABC):
- Adhesions (post-operative, ~75%)
- Bulge (incarcerated hernias)
- Cancer (tumors, intrinsic or extrinsic)
Pathophysiology Cascade:
- Obstruction → Proximal bowel dilation (gas/fluid) → ↑ Intraluminal pressure.
- Bowel wall edema & third-spacing → Hypovolemia & electrolyte shifts.
- Venous & arterial compromise → Ischemia, necrosis, perforation.

Small Bowel Obstruction: Causes

⭐ Strangulation is a surgical emergency, marked by fever, tachycardia, leukocytosis, and localized pain. It implies compromised blood flow requiring immediate intervention to prevent bowel necrosis.

Clinical Presentation - The Gut's Cry for Help

Cardinal Symptoms (📌 CAVO):
- Colicky abdominal pain: Initially periumbilical & crampy; becomes constant & severe with strangulation.
- Abdominal distension: More pronounced in distal SBO.
- Vomiting: Early, bilious (proximal SBO) vs. late, feculent (distal SBO).
- Obstipation: Failure to pass stool or flatus; a late finding indicating complete obstruction.
Physical Exam Findings:
- Bowel sounds: Early high-pitched "tinkles" → Late hypoactive/absent sounds.
- ⚠️ Peritoneal signs (e.g., rebound tenderness, guarding) suggest strangulation or perforation.

⭐ A patient with partial SBO may still pass flatus or have diarrhea.

Diagnosis - Peeking Inside the Pipes

Labs: CBC, BMP, lactate, and type & screen. Look for leukocytosis, electrolyte abnormalities, and signs of ischemia (↑ lactate).
Abdominal X-ray (AXR): Initial imaging.
- Dilated small bowel loops (>3 cm).
- Multiple air-fluid levels on upright film.
- Paucity of gas in the colon.

Upright Abdominal X-ray: Small Bowel Obstruction

CT Scan (Abdomen/Pelvis with IV contrast): Gold standard for diagnosis.
- Confirms diagnosis, identifies location, severity, and etiology (e.g., hernia, mass).
- Determines presence of complications (ischemia, perforation).

⭐ Exam Favorite: The most important finding on CT is the transition point-a discrete location where the bowel caliber changes from dilated proximal loops to collapsed distal loops, pinpointing the obstruction site.

Management - Untangling the Knot

Initial Stabilization (Conservative): The cornerstone for all SBO patients.
- NPO (Nil Per Os): Bowel rest is critical.
- IV Fluids: Aggressive resuscitation with isotonic crystalloids (Lactated Ringer's or Normal Saline) to correct dehydration.
- Nasogastric (NG) Tube: Decompresses the stomach and proximal bowel, reducing distention and vomiting.
- Monitor urine output (goal > 0.5 mL/kg/hr) and electrolytes.
Definitive Management: The decision to operate hinges on the presence of complications.

⭐ In a "virgin" abdomen (no prior surgery), a hernia is the most likely cause of SBO. Always perform a thorough physical exam to check for incarcerated hernias, as this is a surgical emergency.

High‑Yield Points - ⚡ Biggest Takeaways

Adhesions from prior surgery are the #1 cause of SBO.

Cardinal features are colicky abdominal pain, vomiting, abdominal distension, and obstipation.

Exam reveals high-pitched, tinkling bowel sounds early on, which later become hypoactive.

Abdominal X-ray shows dilated small bowel loops (>'''3 cm''') with air-fluid levels.

CT scan is the diagnostic standard, confirming the diagnosis and identifying the transition point.

Initial management is conservative: NPO, IV fluids, and NG tube decompression.

Peritoneal signs, acidosis, or failure to resolve indicate strangulation and require urgent surgery.

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