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Discover the causes, symptoms, and life-saving treatments for peritonitis, a potentially fatal inflammation of the abdominal cavity, in this comprehensive and informative article.

USMLE Guide: Peritonitis


Peritonitis is a serious medical condition characterized by inflammation of the peritoneum, the thin tissue lining the inner wall of the abdomen and covering the abdominal organs. It is often caused by infection or injury and can lead to life-threatening complications if not promptly diagnosed and treated. This USMLE guide aims to provide a comprehensive overview of peritonitis, including its etiology, clinical presentation, diagnosis, and management.


Peritonitis can arise from various causes, including:

  1. Infection: The most common cause of peritonitis is bacterial infection. It may result from the rupture of a gastrointestinal organ, such as the appendix or colon, leading to the release of bacteria into the peritoneal cavity. Common pathogens include Escherichia coli, Klebsiella pneumoniae, Streptococcus species, and Bacteroides fragilis.

  2. Chemical irritation: Certain chemicals, such as bile or gastric acid, can cause peritonitis if they leak into the peritoneal cavity due to trauma or perforation of organs.

  3. Foreign bodies: Peritonitis may also arise from the presence of foreign bodies, such as intra-abdominal sutures or surgical drains, which can introduce bacteria or cause local irritation.

  4. Complications of peritoneal dialysis: Peritonitis can occur as a complication of peritoneal dialysis, an artificial method of removing waste products in patients with renal failure.

Clinical Presentation

Patients with peritonitis often present with the following signs and symptoms:

  1. Abdominal pain: Severe and diffuse abdominal pain is a hallmark symptom of peritonitis. The pain is often aggravated by movement or palpation.

  2. Tenderness: physical examination reveals abdominal tenderness, particularly over the area affected by peritonitis.

  3. Fever and chills: Infection-related peritonitis is often accompanied by fever, chills, and other signs of systemic inflammation.

  4. Abdominal distension: As the inflammation progresses, patients may develop abdominal distension due to fluid accumulation.

  5. Nausea and vomiting: Gastrointestinal symptoms, such as nausea and vomiting, are common in peritonitis.


The diagnosis of peritonitis involves a combination of clinical evaluation, laboratory tests, and imaging studies. The following diagnostic methods are commonly employed:

  1. Physical examination: A thorough abdominal examination is crucial for assessing abdominal tenderness, guarding, and signs of peritoneal irritation.

  2. Laboratory tests: Blood tests, including complete blood count (CBC), C-reactive protein (CRP), and blood cultures, aid in identifying infection and systemic inflammation.

  3. Abdominal imaging: Imaging studies, such as abdominal X-ray or computed tomography (CT) scan, are performed to identify the underlying cause of peritonitis, such as bowel perforation or abscess formation.

  4. Paracentesis: In suspected cases of peritonitis, performing a paracentesis, which involves removing a sample of peritoneal fluid for analysis, can help determine the presence of infection and guide appropriate antibiotic therapy.


The management of peritonitis involves both medical and surgical interventions, depending on the underlying cause and severity of the condition:

  1. Supportive care: Patients with peritonitis are initially stabilized with intravenous fluids, pain control, and broad-spectrum antibiotics to cover common pathogens.

  2. Surgical intervention: In cases of perforation or abscess formation, surgical exploration and repair are necessary. This may involve procedures such as an appendectomy, bowel resection, or drainage of abscesses.

  3. Source control: Efforts are made to identify and treat the underlying cause of peritonitis, such as removing foreign bodies or treating the primary infection.

  4. Antibiotic therapy: The choice of antibiotics is guided by culture and sensitivity results from the peritoneal fluid analysis. Empiric antibiotic therapy should cover both aerobic and anaerobic bacteria commonly seen in intra-abdominal infections.

  5. Monitoring and follow-up: Close monitoring of the patient's clinical response to therapy, including resolution of symptoms and normalization of laboratory markers, is essential. Follow-up imaging studies may be performed to evaluate the effectiveness of surgical interventions.


Peritonitis is a potentially life-threatening condition characterized by inflammation of the peritoneum. Prompt diagnosis and appropriate management are vital to prevent complications and improve patient outcomes. Understanding the etiology, clinical presentation, diagnostic methods, and management principles of peritonitis is essential for medical practitioners, including those preparing for the USMLE examination.

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