L24 Peritonitis and Intra-abdominal infection

Question 1

Differentiate between Primary/spontaneous, Secondary, Localised and generalised peritonitis

Answer 1

1’: due to bacterial translocation, haematogenous spread or iatrogenic contamination of the abdomen without a GI tract defect.
- usually monomicrobial and in those with ascites

2’: due to direct contamination of the peritoneum from perforation in the GI or urogenital tracts
- usually polymicrobial

Localised: peritoneal signs limited to one or two abdo quadrants, suggesting contained process

Generalised: widespread inflammation of the peritoneum across all 4 quadrants

Question 2

Describe the structure of the peritoneum

Answer 2

Semi-permeable membrane made by 2 layers of lined by mesothelial cells with peritoneal fluid in between as an immune barrier.
There is a lymphatics drainage across the peritoneum.

Question 3

What is the pathophysiology of Peritonitis

Answer 3

1. Bacteria enters the peritoneum as an extension of localised inflammatory condition/ perforation/ post op anastomotic leak
2. Induces inflammatory response
3. Greater omentum acts as a physical barrier to confine infection and for rapid neutrophil deployment, which may contain the infection
4. IF unable to contain, then generalised peritonitis which due to rapid clearance from lymphatic system turns into Systemic inflammatory response and Bacteremia
5. Spontaneous resolution or result in confined abscess with diffuse peritonitis.

Question 4

What disease processes may cause peritonitis

Answer 4

Inflammatory condition within the peritoneum: This excludes the GU tract/kidneys and the mediastinum

eg. Cholecystitis, perforated gastric ulcer, large bowel obstruction

Question 5

What features do you have to look when taking history and exam of someone presenting with peritonitis

Answer 5

1. Overall unwellness: signs of Sepsis : fever, hypotension
2. Where has the pain started-> migrated/ prior history of initial source of peritonism
3. Confirm peritonism. Abdominal rigidity, rebound tenderness or guarding
4. Generalised or Localised?

Question 6

What is the general management of patients with peritonitis

Answer 6

If sepsis
1. Fluid resuscitation and blood pressure support
Then
2. Samples for microbiology - blood cultures, surgical samples or aspirate (pus vs swab)
3. Broad spectrum antibiotics to cover potential pathogens
4. Early source control: abscess needs draining, perforation/appendicitis requires surgery
5. ​De-escalation of antibiotic based on microbiology to give narrowest spectrum you can. Gross antibiotics generally 5-7 days

Question 7

What is diverticulitis

Answer 7

Obstruction of the neck of a diverticulus (common outpouching of the colon) with a faecolith which can seed bacteria leading to inflammation

Question 8

What are good broad spectrum antibiotics with good aerobic coverage and good anaerobic coverage (B. fragilis +/- Enterococcal coverage)

Answer 8

1. Amoxycillin –>enterococci +
   Gentamicin–> gram - aerobes +
   Metronidazole –> anaerobes
2. Cefuroxime + Metronidazole (no Enterococcal coverage unless you use Augmentin as well)
3. If ESBL then use Meropenem (carbapenem with wide range of spectrum)

Question 9

What type of antibiotic is Gentamicin, mech of action what is the target, and what are its uses

Answer 9

• Bactericidal aminoglycoside. It inhibits bacterial protein synthesis. It has poor CSF penetration
• Targets AEROBIC gram negative bacteria including enterobacteriae, Pseudomonas aeruginosa, Acinetobacter because it needs the aerobic metabolism to activate antibacterial effect.
• Used to reduce mortality in those with intra-abdominal septic shock but doesn’t influence abscess formation which is done by metronidazole.

Question 10

What are the SE, dosing, and management of SE of Gentamicin

Answer 10

• SE: Nephrotoxicity, and irreversible Ototoxicity/vestibular toxicity is common and occur with one dose although more likely with prolonged exposure.
• Rarely neuromuscular blockade myasthenia gravis/ concurrent succinylcholine use.

Dosing is based on lean body weight, reduced in kidney disease.
There is therapeutic drug monitoring to avoid toxicity (checking the trough level prior to next dose) and there is no more than 3 days duration.

Question 11

What are the likely bacteria to cause peritonitis - O2, gram, complications

Answer 11

Bacteria are derived from local flora of GI tract. Recent antibiotic exposure/ flora disruption can cause disease allowing ESBL organisms

• Aerobic gram - : E coli, Kiebsella, Enterobacter –> sepsis/death
• Anaerobic gram -: Bacteroides fragilis –> abscess
• Anaerobic gram + (gut dwelling) : Enterococci
• Less commonly : P. aeruginosa, candida and s aureus.