Ch21: Peritonitis & Intra-abdominal Infection（腹膜炎与腹腔感染）

Preparatory Mindset

Peritonitis = inflammation of the peritoneum — primary (spontaneous), secondary (perforation — the surgical type), and tertiary (persistent). The lectures (Dr. Pan 5.2 acute suppurative peritonitis 11.8KB + Jason Ding 14.2 legacy) cover classification, clinical features (peritonism), and management (source control + antibiotics + resuscitation).

Exam mindset: secondary peritonitis from a perforated viscus (appendicitis, peptic ulcer, diverticulitis, trauma) is the surgical core — the principles: resuscitate, source control (operation), antibiotics, and drain. Know the peritonism signs (guarding, rigidity, rebound, absent bowel sounds) and the acute abdomen differential.

Core Concepts

1. Definition & classification (MUST KNOW)

1. Primary (spontaneous) peritonitis (原发性): no obvious intra-abdominal source — bacterial translocation in ascites (cirrhosis, nephrotic syndrome, children); usually monomicrobial (pneumococcus, E. coli, GAS); treat medically (antibiotics) — do NOT operate 2. Secondary peritonitis (继发性) — SURGICAL: from perforation/rupture/contamination of a viscus: - Perforated peptic ulcer, acute appendicitis, diverticulitis, cholecystitis, bowel obstruction/strangulation, trauma (bowel rupture), anastomotic leak, pancreatitis, ischemic bowel - Polymicrobial (gut flora: E. coli, Enterococcus, anaerobes/Bacteroides) - Treatment: source control (surgery) + antibiotics — the core surgical disease 3. Tertiary peritonitis (第三类): persistent/recurrent peritonitis after adequate source control — immunocompromised, ICU; resistant organisms (Candida, Enterococcus, Pseudomonas); mortality high

• Peritonitis: acute or chronic inflammation of the peritoneum
• Classification:
• Intra-abdominal abscess (腹腔脓肿): localized pus after peritonitis — subphrenic, pelvic, paracolic, interloop; treatment: percutaneous drainage (radiology) or surgical drainage + antibiotics

2. Pathophysiology (MUST KNOW)

• Chemical phase (initial): sterile inflammation (gastric acid, bile, pancreatic enzymes) — in perforated ulcer, early peritonitis is chemical
• Bacterial phase: contamination → polymicrobial infection → edema, exudate, fibrinous adhesions, abscess formation
• Systemic: fluid shift (third-space loss → hypovolemia), ileus, SIRS → sepsis → septic shock → MODS; intra-abdominal hypertension/compartment syndrome
• Consequences: peritonitis → ileus, respiratory embarrassment (splinting), hypovolemia, endotoxemia

3. Clinical features (MUST KNOW)

- Tenderness (压痛) - Guarding & rigidity (肌紧张/板状腹) — board-like rigidity in perforated ulcer - Rebound tenderness (反跳痛) - Absent bowel sounds (ileus), abdominal distension

• Symptoms: abdominal pain (progressive, severe), anorexia, nausea/vomiting, fever, chills; pain site hints the source (RIF = appendicitis; epigastric = ulcer; LIF = diverticulitis)
• Signs — "peritonism" (腹膜刺激征) (MUST KNOW):
• Systemic: fever, tachycardia, hypotension (sepsis/shock), dehydration, oliguria, tachypnea
• Special: rectal exam (pelvic tenderness/abscess — "pelvic peritonitis"), vaginal exam in women

4. Investigations (MUST KNOW)

- Erect CXR: free air under the diaphragm (pneumoperitoneum) — perforated viscus (~70% of perforations show free air; NOT always — retroperitoneal duodenal/colonic perforation may not) - CT abdomen with contrast: the key study — identifies the source (appendicitis, diverticulitis, abscess), free fluid/air, collections; guides drainage - US: fast, for gallbladder/biliary, ascites, abscess, free fluid

• Bloods: WBC ↑, CRP ↑, lactate (sepsis), ABG, electrolytes/renal (dehydration), LFTs/amylase (pancreatitis)
• Imaging:
• Diagnostic paracentesis: ascites analysis (primary peritonitis — neutrophils >250), bile/bowel content (secondary)

5. Management (MUST KNOW)

- Surgery (laparotomy/laparoscopy): find & treat the source — appendectomy, repair/resect perforated ulcer (omentopexy), resection of perforated diverticulum/ischemic bowel, washout (peritoneal lavage), drain collections - Percutaneous drainage for well-defined abscesses - Damage control in the unstable (resect, pack, leave open, re-operate)

• Resuscitation (first): IV fluids (crystalloid), electrolyte correction, oxygen, NG tube (decompression), urinary catheter (monitor output), analgesia (after diagnosis), broad-spectrum IV antibiotics (empiric: piperacillin-tazobactam or carbapenem ± metronidazole/antifungal)
• Source control (the essential step — MUST KNOW):
• Postoperative: ICU, continued antibiotics (directed by cultures), drainage management, nutrition (early enteral when possible), monitor for persistent infection/abscess (repeat CT → drain), tertiary peritonitis management (antifungals, source re-evaluation)
• Primary peritonitis (spontaneous): medical — antibiotics (third-generation cephalosporin), treat the underlying (cirrhosis, ascites — consider TIPS/transplant), NO surgery (unless abscess/failure)
• Antibiotics: empiric broad-spectrum covering gram-negatives + anaerobes (± enterococcus/yeast in high risk); culture-directed narrowing; duration: 4-7 days if source controlled (stop when clinically well — not fixed courses)

6. Intra-abdominal abscess (MUST KNOW)

• Sites: subphrenic, pelvic (pouch of Douglas), paracolic, interloop, psoas, liver
• Clinical: persistent fever after peritonitis/surgery, ileus, localized tenderness; pelvic abscess → diarrhea/tenesmus; subphrenic → shoulder pain, chest signs
• Diagnosis: CT (definitive); US for subphrenic/pelvic
• Treatment: percutaneous drainage (US/CT-guided) ± antibiotics; surgical drainage if not accessible/fails; drain the pus, culture
• Subphrenic abscess: after upper abdominal surgery/perforation — fever, hiccups, chest findings

High-Yield Points

• Primary = spontaneous (cirrhosis ascites) — MEDICAL (antibiotics, no surgery); Secondary = perforation — SURGICAL (source control); Tertiary = persistent ICU
• Peritonism: tenderness + guarding/rigidity + rebound + absent bowel sounds
• Free air under the diaphragm = perforated viscus (erect CXR)
• Secondary peritonitis is polymicrobial (gut flora: E. coli + anaerobes)
• Management: resuscitate + broad-spectrum antibiotics + SOURCE CONTROL (surgery/drainage) + lavage/drains
• CT = key imaging; percutaneous drainage for abscess
• Post-op fever = think intra-abdominal abscess (repeat CT, drain)
• Primary peritonitis in ascites: paracentesis neutrophils >250 → antibiotics
• Appendicitis → RIF; perforated ulcer → epigastric/board-like; diverticulitis → LIF
• Antibiotics: 4-7 days after source control (culture-directed)

Topic Summary

Peritonitis: primary (spontaneous, cirrhotic ascites — medical), secondary (perforation — the surgical core, polymicrobial, needs source control), tertiary (persistent ICU). Peritonism = tenderness + guarding/rigidity + rebound + absent bowel sounds. Free air on erect CXR = perforation; CT is the key imaging. Management: resuscitate (fluids, antibiotics empiric broad-spectrum, NG, monitoring) + source control (laparotomy/laparoscopy: appendectomy, ulcer repair, bowel resection; lavage; drainage) + postoperative ICU/cultures/nutrition; well-defined abscesses → percutaneous drainage. Complications: abscess (subphrenic, pelvic — post-op fever), ileus, sepsis/MODS, tertiary peritonitis. Primary peritonitis: paracentesis (neutrophils >250) + antibiotics, no surgery.