A 42-year-old man with chronic hepatitis C is admitted to the hospital because of jaundice and abdominal distention. He is diagnosed with decompensated liver cirrhosis, and treatment with diuretics is begun. Two days after admission, he develops abdominal pain and fever. Physical examination shows tense ascites and diffuse abdominal tenderness. Paracentesis yields cloudy fluid with elevated polymorphonuclear (PMN) leukocyte count. A drug with which of the following mechanisms is most appropriate for this patient's condition?

Inhibition of bacterial peptidoglycan crosslinking

Free radical creation within bacterial cell

Inhibition of bacterial 50S subunit

Inhibition of bacterial RNA polymerase

Inhibition of bacterial DNA gyrase

A 41-year-old woman is brought to the emergency department with the acute-onset of severe abdominal pain for the past 2 hours. She has a history of frequent episodes of vague abdominal pain, but they have never been this severe. Every time she has had pain, it would resolve after eating a meal. Her past medical history is otherwise insignificant. Her vital signs include: blood pressure 121/77 mm Hg, pulse 91/min, respiratory rate 21/min, and temperature 37°C (98.6°F). On examination, her abdomen is flat and rigid. Which of the following is the next best step in evaluating this patient’s discomfort and stomach pain by physical exam?

Elicit shifting dullness of the abdomen

Perform light palpation at the point of maximal pain

Attempt to perform a deep, slow palpation with quick release

Percuss the point of maximal pain

A 68-year-old man presents to the emergency department with left lower quadrant abdominal pain and fever for 1 day. He states during this time frame he has had weight loss and a decreased appetite. The patient had surgery for a ruptured Achilles tendon 1 month ago and is still recovering but is otherwise generally healthy. His temperature is 102°F (38.9°C), blood pressure is 154/94 mmHg, pulse is 90/min, respirations are 15/min, and oxygen saturation is 98% on room air. Physical exam is remarkable for an uncomfortable and thin man with left lower quadrant abdominal tenderness without rebound findings. Fecal occult test for blood is positive. Laboratory studies are ordered as seen below. Hemoglobin: 10 g/dL Hematocrit: 30% Leukocyte count: 3,500/mm^3 with normal differential Platelet count: 157,000/mm^3 Which of the following is the most appropriate next step in management?

Ciprofloxacin and metronidazole

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?"

A 12-month-old boy is brought to the emergency department by his mother for several hours of crying and severe abdominal pain, followed by dark and bloody stools in the last hour. The mother reports that she did not note any vomiting or fevers leading up to this incident. She does report that the boy and his 7-year-old sister recently had “stomach bugs” but that both have been fine and that the sister has gone back to school. The boy was born by spontaneous vaginal delivery at 39 weeks and 5 days after a normal pregnancy. His temperature is 100.4°F (38.0°C), blood pressure is 96/72 mmHg, pulse is 90/min, respirations are 22/min. Which of the following was most likely to play a role in the pathogenesis of this patient’s disease?

Embolism to the mesenteric vessels

Failure of neural crest migration

A 52-year-old-woman presents to an urgent care clinic with right upper quadrant pain for the past few hours. She admits to having similar episodes of pain in the past but milder than today. Past medical history is insignificant. She took an antacid, but it did not help. Her temperature is 37°C (98.6°F ), respirations are 16/min, pulse is 78/min, and blood pressure is 122/98 mm Hg. Physical examination is normal, and she says that her pain has subsided. The urgent care provider suspects she has cholecystitis, so she undergoes a limited abdominal ultrasound to confirm it. However, no evidence of cholecystitis is seen with ultrasound, but adenomyomatosis of the gallbladder is incidentally noted. The patient has no clinical features suspicious for malignancy. What is the next best step in the management of this patient?

Endoscopic retrograde cholangiopancreatography

Magnetic resonance cholangiopancreatography

A 49-year-old woman with a history of hepatitis C cirrhosis complicated by esophageal varices, ascites, and hepatic encephalopathy presents with 1 week of increasing abdominal discomfort. Currently, she takes lactulose, rifaximin, furosemide, and spironolactone. On physical examination, she has mild asterixis, generalized jaundice, and a distended abdomen with positive fluid wave. Diagnostic paracentesis yields a WBC count of 1196/uL with 85% neutrophils. Which of the following is the most appropriate treatment?

Transjugular intrahepatic portosystemic shunt placement

Large volume paracentesis with albumin

Increased furosemide and spironolactone

Intra-abdominal infections for USMLE Step 1: High-Yield Internal Medicine Lessons

Intra-abdominal Infections - Guts Under Siege

Etiology: Peritonitis (inflammation of peritoneum) or Abscess (walled-off infection). Often polymicrobial from gut flora leakage (e.g., perforation, diverticulitis).
Pathogens: Gram-negatives (E. coli, Klebsiella) & anaerobes (Bacteroides fragilis).
Presentation: Fever, tachycardia, severe abdominal pain with guarding or rebound tenderness.
Diagnosis: CT Abdomen/Pelvis with IV contrast is the gold standard to identify abscesses, free air, or inflammation.

CT scan: Intra-abdominal abscess with air-fluid level

⭐ Source control is paramount! Antibiotics alone are insufficient for abscesses or significant perforations. Management requires prompt surgical intervention or percutaneous drainage.

Diagnosis & Workup - Bellyache Breakdown

Initial Assessment: History (acute onset, fever, focal pain) & physical exam (guarding, rebound tenderness).
Labs:
- CBC (leukocytosis with left shift), CMP.
- ↑ Lactate, ↑ CRP, ↑ Procalcitonin.
- Blood cultures x2 (before antibiotics).
- Amylase/Lipase for pancreatitis.
Imaging: Modality depends on suspected source.

⭐ SBP Diagnosis: For ascites, perform paracentesis. A peritoneal fluid absolute neutrophil count (ANC) of >250 cells/mm³ is diagnostic for Spontaneous Bacterial Peritonitis.

Management Principles - Drain & Tame

Core tenets: 1) Resuscitate, 2) Drain (Source Control), 3) Tame (Antibiotics).

Source Control: Crucial first step. Remove infected/necrotic tissue & drain abscesses.
- Percutaneous catheter drainage (PCD) for simple abscesses.
- Surgical exploration (laparotomy/laparoscopy) for complex collections or diffuse peritonitis.
Antibiotics: Broad-spectrum empiric therapy, then tailor to culture results.
- Community-Acquired: Cover GNRs & anaerobes (e.g., Ceftriaxone + Metronidazole; Piperacillin-Tazobactam).
- Hospital-Acquired: Broader coverage needed (e.g., Carbapenems).

⭐ Failure to improve in 48-72h despite antibiotics suggests inadequate source control or resistant organisms.

Common Culprits - A Rogues' Gallery

The usual suspects are gut-derived gram-negative aerobes and anaerobes. Think polymicrobial, especially after perforation.

Site of Infection	Common Pathogens	Key Feature
Biliary Tract	E. coli, Klebsiella, Enterococcus	Ascending infection
Liver Abscess	K. pneumoniae, E. coli, Bacteroides	Single or multiple
SBP	Monomicrobial: E. coli, Klebsiella	In cirrhosis/ascites
Secondary Peritonitis	Polymicrobial: E. coli, B. fragilis	Gut perforation

High‑Yield Points - ⚡ Biggest Takeaways

Spontaneous Bacterial Peritonitis (SBP) in cirrhosis requires paracentesis showing PMN > 250 cells/mm³; treat with third-gen cephalosporins.

Secondary peritonitis from a perforated viscus is a surgical emergency requiring broad-spectrum antibiotics.

Diverticulitis classically causes LLQ pain; CT scan is the best diagnostic test.

Appendicitis presents with migratory RLQ pain and requires appendectomy.

Acute cholecystitis and cholangitis cause RUQ pain; ultrasound is the initial imaging of choice.

Liver abscesses require drainage and targeted antibiotics.

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