Describe the clinical features and diagnostic workup of a suspected case of peritonitis.

Clinical Features of Peritonitis

The clinical presentation of peritonitis can vary depending on the underlying cause, the extent of inflammation (localized or generalized), and the patient's overall health. However, certain cardinal signs and symptoms are consistently observed in suspected cases.

1. Abdominal Pain

• Onset and Character: Pain typically starts as a generalized dull ache (visceral pain) and may become sharp, severe, and constant, localizing to the affected area as the parietal peritoneum becomes involved (somatic pain). It often worsens with any movement, coughing, or deep breathing.
• Location: Generalized abdominal pain is common in diffuse peritonitis, while localized pain can indicate the site of the primary pathology (e.g., right lower quadrant pain in appendicitis, epigastric pain in perforated peptic ulcer).

2. Abdominal Tenderness and Rigidity

• Tenderness: Marked tenderness to palpation is a hallmark sign, often most intense over the inflamed area.
• Rebound Tenderness: Pain experienced upon rapid release of pressure after deep palpation is a strong indicator of peritoneal irritation.
• Guarding: Involuntary spasm of the abdominal muscles (rigidity or "board-like" abdomen) is a crucial sign, especially in generalized peritonitis, as the body attempts to protect the inflamed area.

3. Systemic Symptoms

• Fever and Chills: Common indicators of infection and inflammation.
• Tachycardia: Increased heart rate due to pain, fever, or hypovolemia.
• Nausea and Vomiting: Often present due to paralytic ileus (temporary paralysis of the intestines) which accompanies peritoneal inflammation.
• Anorexia: Loss of appetite.
• Malaise and Fatigue: General feeling of unwellness.
• Altered Bowel Habits: Constipation or inability to pass flatus due to ileus. Reduced urine output may also be observed.

4. Signs of Shock (in severe cases)

• Hypotension: Low blood pressure.
• Cold, Clammy Skin: Due to peripheral vasoconstriction.
• Oliguria: Decreased urine output.
• Altered Mental Status: Confusion or lethargy.

5. Specific Presentations (e.g., Peritoneal Dialysis-Related Peritonitis)

• Cloudy Dialysis Fluid: The most common sign.
• Abdominal Pain and Fever: May be less severe than in other forms of peritonitis.

Diagnostic Workup of a Suspected Case of Peritonitis

A systematic and rapid diagnostic approach is essential to confirm peritonitis, identify its cause, and guide appropriate management.

1. History and Physical Examination

• Detailed History: Inquire about the onset, character, radiation, and aggravating/alleviating factors of pain. Elicit information on associated symptoms (nausea, vomiting, fever, bowel habits), medical history (e.g., liver disease, recent surgery, peritoneal dialysis), and medication use.
• Physical Examination:
• General Appearance: Assess for signs of distress, dehydration, or shock.
• Abdominal Examination:
  • Inspection: Look for distension, scars, or visible peristalsis.
  • Auscultation: Listen for bowel sounds (often diminished or absent in ileus).
  • Palpation: Systematically palpate the abdomen, starting away from the painful area, to assess tenderness, rebound tenderness, and guarding/rigidity.
  • Percussion: Elicit percussion tenderness, which indicates peritoneal irritation.
• Digital Rectal Examination (DRE): May reveal tenderness in the pouch of Douglas.
• Pelvic Examination (in females): To rule out gynecological causes.

2. Laboratory Investigations

• Complete Blood Count (CBC):
  • Leukocytosis: Elevated white blood cell count (neutrophilia) is common, indicating infection or inflammation.
  • Hemoglobin: May be low in cases of bleeding or severe inflammation.
• Inflammatory Markers:
  • C-Reactive Protein (CRP) and Procalcitonin: Elevated levels indicate systemic inflammation and bacterial infection, respectively.
• Electrolytes, Urea, Creatinine: To assess hydration status, renal function, and electrolyte imbalances resulting from vomiting or fluid shifts.
• Liver Function Tests (LFTs) and Amylase/Lipase: To investigate hepatobiliary or pancreatic pathology as potential causes.
• Blood Cultures: Essential in suspected sepsis to identify the causative organism and guide antibiotic therapy.
• Urinalysis: To rule out urinary tract infection or pathology.

3. Peritoneal Fluid Analysis (Abdominocentesis/Paracentesis)

This is a crucial diagnostic step, especially in patients with ascites or peritoneal dialysis-related peritonitis. A sample of peritoneal fluid is aspirated and analyzed.

• Cell Count and Differential: An elevated white blood cell count (especially polymorphonuclear leukocytes >250 cells/mm³ or >100 cells/µL in peritoneal dialysis effluent) strongly suggests peritonitis.
• Gram Stain: For rapid identification of bacteria or fungi.
• Culture and Sensitivity: The gold standard for identifying the causative microorganism and determining antibiotic susceptibility. Blood culture bottles are preferred for culturing peritoneal dialysis effluent.
• Biochemical Analysis:
  • Protein and LDH: Elevated levels.
  • Glucose: Low levels.
  • Amylase/Lipase: Elevated if pancreatic leak is suspected.
  • Bilirubin/Creatinine: Elevated if biliary or urinary leak is suspected.

4. Imaging Studies

• Abdominal X-rays (Plain Radiographs):
  • Erect Chest X-ray and Abdominal X-ray: May show free air under the diaphragm (pneumoperitoneum), indicative of hollow viscus perforation.
  • Dilated Bowel Loops: Suggestive of paralytic ileus.
• Ultrasound (USG) Abdomen:
  • Can detect fluid collections, abscesses, and some causes like appendicitis, cholecystitis, or gynecological pathologies.
  • Useful for guiding paracentesis.
• Computed Tomography (CT) Scan of Abdomen and Pelvis:
  • Diagnostic Study of Choice: Highly sensitive and specific for identifying fluid collections, abscesses, inflammation, and the underlying pathology (e.g., perforated viscus, diverticulitis, pancreatitis).
  • Often performed with oral and intravenous contrast to enhance visualization.
• Magnetic Resonance Imaging (MRI): May be used in specific situations, especially when radiation exposure is a concern (e.g., pregnancy) or for better soft tissue differentiation.

5. Diagnostic Laparoscopy/Laparotomy

• In cases of diagnostic uncertainty, or when imaging is inconclusive, diagnostic laparoscopy allows direct visualization of the peritoneal cavity, identification of the source of infection/inflammation, and therapeutic intervention.
• Emergency laparotomy is indicated in cases of clear surgical peritonitis (e.g., generalized peritonitis with perforation).

Recent Advances in Diagnosis

• Point-of-Care (POC) Molecular Tests: Rapid diagnostic tests for specific pathogens, especially relevant in peritoneal dialysis-related peritonitis.
• Leukocyte Esterase Reagent Strips: Used for rapid bedside detection of leukocytes in peritoneal fluid, offering quick screening.
• Genetic Sequencing and Mass Spectrometry: Advanced techniques for faster and more accurate identification of microorganisms, including those that are difficult to culture.
• Biomarkers: Research into novel biomarkers like interleukin-6 (IL-6) and matrix metalloproteinase-8 (MMP-8) in peritoneal fluid for early and specific diagnosis.
• Machine Learning Algorithms: Applied to clinical data and immune fingerprints to predict peritonitis and identify pathogens more efficiently.

The timely integration of clinical assessment, laboratory findings, and appropriate imaging is paramount for the accurate diagnosis and subsequent effective management of peritonitis, which often involves broad-spectrum antibiotics and surgical intervention.