Peritonitis is an acute or chronic inflammation of the peritoneum—the serous membrane lining the abdominal cavity and covering the visceral organs. It is a life-threatening condition that requires prompt diagnosis and management.
Anatomical and Physiological Background
The peritoneum is divided into:
- Parietal peritoneum : lines the abdominal wall.
- Visceral peritoneum : covers abdominal organs.
- The peritoneal cavity between these layers normally contains a small amount of sterile serous fluid that permits frictionless organ movement.
Peritoneal fluid is produced and absorbed continuously by mesothelial cells. This dynamic system can be disrupted by infection or chemical irritation, leading to peritonitis .
Classification of Peritonitis
1. Primary (Spontaneous Bacterial Peritonitis - SBP)
- Occurs without evident intra-abdominal source.
- Most common in patients with cirrhosis and ascites .
- Usually monomicrobial (e.g., E. coli , Klebsiella , Streptococcus pneumoniae ).
2. Secondary Peritonitis
- Due to perforation or inflammation of abdominal organs.
- Examples:
- Perforated peptic ulcer
- Ruptured appendix
- Diverticulitis
- Bowel ischemia
- Postoperative leaks
- Usually polymicrobial (aerobes + anaerobes).
3. Tertiary Peritonitis
- Persistent or recurrent infection despite treatment, often seen in ICU settings.
Etiology and Risk Factors
Localized Causes :
- Appendicitis
- Cholecystitis
- Diverticulitis
- Pelvic Inflammatory Disease (e.g., Salpingitis)
Generalized Causes :
- Gastrointestinal perforation (ulcer, ischemia)
- Pancreatic leakage (chemical peritonitis)
- Continuous ambulatory peritoneal dialysis (CAPD)
- Spontaneous bacterial peritonitis (in cirrhotic patients)
Pathophysiology
- Infection or irritants (e.g., bile, pancreatic enzymes) enter the sterile peritoneal cavity.
- Inflammatory cascade is initiated:
- Mast cells release histamine and cytokines
- Increased capillary permeability → fluid shift (third-spacing)
- Influx of neutrophils and macrophages
- Fibrinogen is deposited → fibrin forms to localize infection (may lead to adhesions)
- Complications include:
- Paralytic ileus due to peristalsis inhibition
- Sepsis or septic shock if bacteria/toxins enter the bloodstream
- Multiorgan failure
Clinical Presentation
Local Symptoms :
- Acute onset severe abdominal pain , worsened by movement or coughing
- Abdominal tenderness, guarding, or rigidity
- Rebound tenderness
- Distension
Systemic Symptoms :
- Fever
- Tachycardia, Tachypnea
- Malaise
- Dehydration, oliguria
- Hypotension (in septic shock)
- Encephalopathy (in cirrhosis + SBP)
Physical Examination Findings
- Involuntary guarding of abdominal muscles
- Board-like rigidity
- Absent or decreased bowel sounds (paralytic ileus)
- Rebound tenderness
- Percussion tenderness
- Signs of shock : cold extremities, low BP
Diagnostic Investigations
Laboratory Tests :
- CBC: leukocytosis with left shift
- CRP, ESR: elevated
- Urea, creatinine, electrolytes: assess hydration and renal function
- LFTs: especially in suspected SBP
- Serum amylase/lipase: in pancreatitis
Imaging :
- Erect abdominal X-ray : free air under diaphragm (if perforation)
- Ultrasound/CT scan : detect abscesses, fluid collections
- Laparoscopy : for diagnostic uncertainty or surgical planning
Peritoneal Fluid Analysis (paracentesis):
- Appearance: turbid, purulent
- Cell count: PMNs > 250 cells/μL in SBP
- Gram stain, culture, sensitivity
- Albumin gradient (SAAG) to assess cause
Management
General Supportive Measures :
- IV fluids and electrolyte resuscitation
- NPO and nasogastric tube decompression
- Broad-spectrum antibiotics :
- Common regimens: ceftriaxone + metronidazole , or piperacillin-tazobactam
- Pain control : cautiously, after surgical evaluation
Definitive Treatment :
- Surgical intervention :
- Exploratory laparotomy : indicated in secondary peritonitis
- Control of source: e.g., appendectomy, ulcer repair
- Peritoneal lavage : removes pus and necrotic material
- Abscess drainage (ultrasound or CT-guided)
- Management of underlying conditions (e.g., cirrhosis, dialysis)
For Spontaneous Bacterial Peritonitis (SBP) :
- Empiric antibiotics: cefotaxime or ceftriaxone
- Consider albumin infusion to prevent hepatorenal syndrome
Complications
- Sepsis and septic shock
- Multiple organ dysfunction syndrome (MODS)
- Intra-abdominal abscess
- Bowel obstruction from adhesions
- Wound dehiscence and infections
- Enterocutaneous fistula formation
Prognosis
- Prognosis depends on:
- Timeliness of diagnosis
- Etiology
- Patient’s comorbidities (e.g., cirrhosis, immunosuppression)
- Mortality is high in untreated cases or with delayed intervention.
High-Yield Summary for NCLEX/USMLE
| Feature | Key Points |
|---|---|
| Common bacteria | E. coli , Klebsiella , Streptococcus , Pseudomonas |
| Classic signs | Board-like abdomen, rebound tenderness, fever |
| First imaging study | Upright abdominal X-ray |
| Definitive diagnosis | Paracentesis (esp. in ascites) |
| Key labs in SBP | PMNs > 250 cells/μL |
| Treatment | Broad-spectrum antibiotics + surgery if needed |
| Surgical indication | Secondary peritonitis (perforated viscus, abscess, etc.) |
