Gastroenterology · Acute Abdomen
The facts most likely to be tested
Spontaneous bacterial peritonitis (SBP) is diagnosed by an ascitic fluid absolute neutrophil count (ANC) ≥ 250 cells/mm³.
Primary peritonitis most commonly occurs in patients with cirrhosis and ascites due to translocation of enteric bacteria.
Secondary peritonitis results from perforation of an abdominal viscus, leading to polymicrobial infection and requiring emergent surgical intervention.
Physical examination findings of rebound tenderness, guarding, and rigidity are classic signs of peritoneal irritation.
Dialysis-associated peritonitis in patients with peritoneal dialysis typically presents with cloudy dialysate effluent and abdominal pain.
Empiric antibiotic therapy for SBP must cover common gram-negative rods and is typically initiated with a third-generation cephalosporin like cefotaxime.
Peritoneal dialysis peritonitis is most frequently caused by Staphylococcus epidermidis or Staphylococcus aureus.
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A 58-year-old male with a history of alcohol-associated cirrhosis presents to the emergency department with a two-day history of diffuse abdominal pain and low-grade fever. Physical examination reveals diffuse abdominal tenderness, rebound tenderness, and guarding. Paracentesis is performed, and the ascitic fluid analysis shows a protein level of 1.2 g/dL and an absolute neutrophil count of 450 cells/mm³.
What is the most appropriate initial management for this patient?
Intravenous cefotaxime
The patient meets the diagnostic criteria for SBP (ANC ≥ 250 cells/mm³), which requires immediate initiation of empiric antibiotic therapy with a third-generation cephalosporin.
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Etiology / Epidemiology
Primary (SBP) occurs in cirrhosis/ascites; secondary follows perforation of a hollow viscus.
Clinical Manifestations
Presents with rigid abdomen, rebound tenderness, and guarding.
Diagnosis
SBP diagnosed via paracentesis with PMN count > 250 cells/µL.
Treatment
Secondary requires surgical exploration; SBP requires cefotaxime.
Prognosis
High mortality if untreated; septic shock is the primary lethal complication.
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Epidemiology & Etiology
Primary spontaneous bacterial peritonitis (SBP) is most common in patients with cirrhosis and ascites. Secondary peritonitis results from perforation, trauma, or postoperative complications. Tertiary peritonitis occurs in critically ill patients with persistent infection despite therapy.
Pertinent Anatomy
The peritoneum is a serous membrane lining the abdominal cavity. Inflammation triggers the somatic pain fibers of the parietal peritoneum, leading to localized, intense pain and abdominal wall rigidity.
Pathophysiology
Bacterial translocation or direct contamination triggers an intense inflammatory response. This leads to third-spacing of fluids, hypovolemia, and potential septic shock. The body attempts to wall off the infection, often resulting in abscess formation.
Clinical Manifestations
Patients present with diffuse abdominal pain, rebound tenderness, and guarding. The abdomen is often described as board-like. Red flags include hypotension, tachycardia, and altered mental status indicating systemic sepsis.
Diagnosis
The gold standard for SBP is paracentesis showing a PMN count > 250 cells/µL. For secondary peritonitis, CT scan of the abdomen/pelvis is the diagnostic study of choice to identify free air or abscesses. Free air on upright CXR confirms perforation.
Treatment
Secondary peritonitis requires surgical exploration and broad-spectrum antibiotics. SBP is treated with cefotaxime or ceftriaxone. Avoid aminoglycosides in SBP due to nephrotoxicity risk in cirrhotic patients. Fluid resuscitation is mandatory.
Prognosis
Prognosis depends on the speed of surgical source control. Complications include sepsis, multi-organ failure, and adhesion-related bowel obstruction. Mortality remains high if the underlying perforation is not addressed.
Differential Diagnosis
Appendicitis: localized RLQ pain with McBurney's point tenderness
Pancreatitis: elevated lipase with epigastric pain radiating to the back
Cholecystitis: RUQ pain with Murphy's sign
Diverticulitis: LLQ pain with fever and leukocytosis
Mesenteric Ischemia: pain out of proportion to physical exam findings