L25: Peritonitis and intra-abdominal infection Flashcards
What is peritonitis?
- Inflammation of peritoneum
- Can be generalised/diffuse or localised/abscess infection
- Primary/spontaneous peritonitis = diffuse bacterial infection without loss of GI integrity (rare, associated with patients with liver disease)
- Secondary = acute infection from loss of GI tract integrity or from infected viscera (most common, related to visceral pathology or post-surgical infection)
- Tertiary = recurrent infection of peritoneal cavity following initial therapy (often defective immunity)
Microbial causative agents
Polymicrobial infection = more than 1 species, synergistic infection (hospital acquired may be one species)
Bacteria:
- Enterobacteriaceae (E. coli, Klebsiella, enterobacter)
- Anaerobes
- Gram neg bacilli (bacteriodes fragilis, prevotella)
- Gram pos cocci (peptostreptococcus)
- Gram pos bacilli (clostridium) - Enterococci
Sources and transmission
Source: more bacteria further down GI (more anaerobic) - stomach, duodenum, jejunum, ileum, colon
Transmission: from GI tract to peritoneum via perforation (secondary peritonitis)
- Mainly from appendicitis, diverticulitis (less so: ulcers, infections/abscess of other organs)
Risk factors for peritonitis
Primary peritonitis = liver disease, portal hypertension, ascites
Secondary peritonitis = appendicitis, diverticulitis, ulcers, CAPD (dialysis), surgery
Tertiary peritonitis = immune deficiencies, previous primary or secondary peritonitis
Pathogenesis of peritonitis
- Bacteria gain entry (normally would be phagocytosed or contained in fibrin clot)
- Bacteria not cleared in presence of nutrients (e.g. Hb) and necrotic tissue
- Bacteria proliferates -> inflammation -> fluid exudate in cavity -> dilutes immune factors and reduces blood volume (hypovolemia)
- Abscess formation (e.g. bacteriodes fragilis - fibrin trap bacteria “hide”) , prevents phagocytosis and immune access (microbial growth continues)
Presentation of peritonitis
- Fever
- Increase resp rate (>20/min), heart rate (>90/min)
- Nausea and vomiting
- Diffuse abdominal pain (may become more localised)
- Rebound tenderness
- Abdominal wall rigidity
Investigations for peritonitis
- Increased blood leukocytes
- CT/US: fluid accumulation, inflammation
- Laparoscopy: diagnostic, may allow treatment
Diagnostic microbiology
Aspirate pus (foul smelling)
Gram stains of pus from abscess:
- Gram neg rods
- Possibly gram pos cocci
- Probably more than one type
Anaerobic and aerobic cultures:
- Culture from pus
- Anaerobic transport swabs
(useful e.g. if antibiotics fail, give idea of range of bacteria present)
Diagnostic tests - anaerobes and bacteriodes
- Because of their fastidiousness, bacteriodes are difficult to isolate, often overlooked
- Often mixed infections e.g. E. coli on MacConkey agar
- Isolation requires aseptic aspiration, transport in an anaerobic environment
- Selective agar (bile aesculin agar produces black colour)
- Gas-liquid chromatography can be used to detect volatile fatty acids produced by anaerobic bacteria
- PCR
- MALD-TOF mass spectrometry
Polymicrobial infection
(Synergy e.g. bacteriodes fragilis and E. coli)
Bacteriodes fragilis:
- Polysaccharide capsule promotes abscess formation (fibrin deposition) and stops phagocytosis
- Produces proteases, degrades complements
- Produce enzymes to stop iron-forming enzymes
E. coli:
- Secretes factors to acquire iron (required for oxygen-forming enzymes produced by body)
Treatment of peritonitis
- Symptomatic (fluids, pain relief, removal/drain pus guided by US/CT)
- Establish cause and control origin (drain pus, dead tissue, corrective surgery)
- Broad spectrum antibiotics (empiric broad spectrum - 1-2 weeks)
Triple therapy or single therapy if kidney and liver problems
Danger of C. difficile infection of GI tract with longer treatment regime
Triple therapy for peritonitis
Enterobacteriaceae (E. coli) = aminoglycoside, fluoroquinolone or 4th generation cephalosporin
Anaerobes (B. fragilis) = clindamycin, metranidazole
Enterococcus = amphicillin
Metronidazole action
- Antibiotic = bactericidal, amoebicidal, trichomoncidal
- Not effective against aerobic and facultatively anaerobic bacteria
- Oxidised by bacteria, interfering with DNA synthesis (exact mechanism not known)
Metronidazole effective against:
- Anaerobic gram-neg bacilli (B. fragilis)
- Anaerobic gram-pos cocci (Clostridium, Eubacterium, anaerobic streptococci)
- Some pathogenic protozoa (Trichomonas vaginalis, Entamoeba histolytica, Giardia lamblia)
Prevention of peritonitis
Prompt diagnosis and treatment of predisposing conditions (e.g. appendicitis)
