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Clinical Pathology G > Intra-abdominal infections > Flashcards

Intra-abdominal infections Flashcards

1
Q

Definition of intra-abdominal infection?

A

Presence of micro-organisms in normally-sterile sites within the abdominal cavity

  • Peritoneal cavity
  • Hepatobiliary tree

Excludes gastroenteritis
- Bowel lumen is a non-sterile site

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2
Q

Why is the proximal small intestine relatively free of microorganisms? What ones are there?

A

Growth inhibited by bile

A few aerobic bacteria and Candida spp.

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3
Q

How many organisms are there normally per gram?

A

10^9-10^11

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4
Q

What is the normally the percentage of anaerobic bacteria?

A

95-99%

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5
Q

What are the normal types of aerobic bacteria in the large intestine?

A

Enterobacteriaceae (enteric Gram-negative bacilli, coliforms)
Gram-positive cocci (mainly enterococci)

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6
Q

What are sources of gastrointestinal infection?

A

Gastrointestinal contents
Blood
External

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7
Q

What are the 3 mechanisms of intra-abdominal infection?

A

Translocation of micro-organisms from gastrointestinal tract lumen to peritoneal cavity
- Intraperitoneal infections

Translocation of micro-organisms along a lumen
- Biliary tract/hepatobiliary infections

Translocation of micro-organisms from an extra-intestinal source

  • Penetrating trauma
  • Haematogenous spread
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8
Q

How does translocation across a wall occur?

A

Perforation
- Perforated appendix, perforated ulcer, perforated diverticulum, malignancy

Loss of integrity
- Ischaemia, strangulation

Surgery
- Seeding at operation, anastomotic leak

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9
Q

How does translocation along a lumen occur?

A

Blockage
- Cholecystitis, cholangitis, hepatic abscess

Iatrogenic
- Instrumentation (e.g. ERCP)

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10
Q

What are the clinical features of a perforated appendix?

A

Disease mainly of children and young adults

Obstruction of lumen of vermiform appendix

  • Lymphoid hyperplasia, faecal obstruction?
  • Results in stagnation of luminal contents, bacterial growth and recruitment of inflammatory cells
  • Build up of intraluminal pressure may result in perforation
  • Escape of luminal contents into peritoneal cavity is “peritonitis”

Severe, generalised pain

Shock

May localise to form “appendix mass”
- Inflamed appendix with adherent covering of omentum and small bowel

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11
Q

What are diverticula and what can their complications include?

A

Herniations of mucosa/submucosa through muscular layer
- Sigmoid and descending colon

Asymptomatic diverticula are very common
- 50% > 70 yrs

Complications

  • Diverticulitis
  • Perforation
  • Pericolic abscess
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12
Q

Why can bowel cancer cause intra-abdominal infections?

A

Intraperitoneal and/or bloodstream infection is an infrequent complication
- Especially associated with Clostridium septicum and Streptococcus gallolyticus (formerly S. bovis) bloodstream infection

Presumably caused by loss of bowel wall integrity due to abnormal malignant tissue

May follow symptoms consistent with bowel malignancy
- e.g. weight loss, alteration of bowel habit, blood in stool etc

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13
Q

What causes ischaemia of the bowel?

A

Interruption of intestinal blood supply

  • Strangulation
  • Arterial occlusion
  • Post-operative
    e. g. aneurysm repair

Gut wall loses structural integrity

Allows translocation of luminal contents

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14
Q

What are the features of post-operative infection?

A

Seeding at operation
- Incidence reduced with bowel preparation/prophylactic antibiotics

Anastomotic leak

Acute infection

  • Abdominal pain and tenderness
  • Shock

Intraperitoneal abscess

  • Walled-off abscess
  • More indolent condition
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15
Q

What is cholecystitis?

A

Inflammation of the gallbladder wall

  • Chemical inflammation
  • Bacterial infection may be cause or result of cholecystitis
    • Cultures positive in c. 50-75% of cases

Associated with obstruction of the cystic duct

  • Gallstones (90%)
  • Other causes
    • Malignancy, surgery, parasitic worms
    • Very occasionally no obstruction
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16
Q

How does cholecystitis present?

A

Fever, right upper quadrant pain, mild jaundice (CBD remains patent)

17
Q

What is emphysematous cholecystitis?

A

Intramural gas in gallbladder wall

18
Q

What is empyema of the gallbladder?

A

Complication of cholecystitis

Frank pus in gallbladder

Presentation is as for cholecystitis but septic presentation

  • Severe pain
  • High fever
  • Chills and rigors
19
Q

What is cholangitis and what causes it?

A

Inflammation/infection of biliary tree (hepatic and common bile ducts)

Same causes as cholecystitis

  • Mainly obstruction of common bile duct
  • Can follow instrumentation (e.g. endoscopic retrograde cholangio-pancreatography, ERCP)
20
Q

How does cholangitis present?

A

Fever (rigors), jaundice and right upper quadrant pain

Presentation may be non-specific

21
Q

What are the routes of infection of pyogenic liver abscesses?

A

Biliary obstruction

Direct spread from other intra-abdominal infections

Haematogenous

  • From mesenteric infection (via hepatic portal vein)
  • From systemic intravascular infection (via hepatic artery)

Penetrating trauma

Idiopathic

22
Q

What are intra-peritoneal abscesses?

A

Localised area of peritonitis with build-up of pus

- Subphrenic, subhepatic, paracolic, pelvic etc.

23
Q

What are the predisposing factors for intra-peritoneal abscess?

A

Perforation

  • Peptic ulcer
  • Perforated appendix
  • Perforated diverticulum

Cholecystitis

Mesenteric ischemia/bowel infarction

Pancreatitis/pancreatic necrosis

Penetrating trauma

Postoperative anastomotic leak

24
Q

How does a non-specific intra-peritoneal abscess present clinically?

A

Sweating, anorexia, wasting

High swinging pyrexia

25
Q

How does a subphrenic abscess present clinically?

A

Pain in shoulder on affected side, persistent hiccup, intercostal tenderness, apparent hepatomegaly (liver displaced downwards, ipsilateral lung collapse with pleural effusion

“Pus somewhere… pus nowhere… pus under the diaphragm.”

26
Q

How does a pelvic abscess present?

A

Urinary frequency

Tenesmus

27
Q

Name some other conditions that can cause intra-abdominal infections?

A

Spontaneous bacterial peritonitis (SBP)
- Infected ascitic fluid

Pancreatic and splenic abscesses

Amoebic abscess
- Entamoeba histolytica

Hydatid cyst
- Echinococcus granulosus

Ileo-caecal tuberculosis
- Mycobacterium tuberculosis

28
Q

Name some aerobic gram-negative bacilli

A

Enterobacteriaceae (coliforms)

  • Predominantly E. coli
    • Also Enterobacter, Citrobacter, Klebsiella, Proteus, Serratia, spp. etc.

Pseudomonas spp.

29
Q

Name some Anaerobic Gram-negative bacilli

A

Bacteroides spp., Prevotella spp.

30
Q

Name some Aerobic Gram-positive cocci

A

Enterococcus spp.

Occasionally milleri-group streptococci (S. anginosus/constellatus group)

31
Q

Name an anaerobic gram-positive bacilli

A

Clostridium spp

32
Q

Hepatobiliary tract infections involve GI flora from what level?

A

usually involve lower GI flora, despite duodenal origin

33
Q

What blood tests may be done when intra-abdominal infection is suspected?

A

Full blood count: neutrophilia/neutropenia
C-reactive protein: raised
Liver function tests: abnormal in hepatobiliary disease

34
Q

What types of imaging would be used for suspected intra-abdominal infections and what would you be looking for?

A

Chest x-ray
- Consolidation, pleural effusion adjacent to infected area (e.g. subphrenic abscess)

Abdominal ultrasound

  • Abdominal masses
  • Free fluid
  • Dilated bile ducts

Abdominal CT scan
(Higher definition than ultrasound)

35
Q

What other microbiological investigations could you perform?

A

Samples to test

  • Blood
  • Peritoneal fluid
  • Ultrasound/CT guided drainage fluid

Microscopy, culture and sensitivity testing

36
Q

What are the principals of antimicrobial therapy for intra-abdominal infections?

A

Treat underlying condition
- e.g. resection, anastomosis, abscess drainage, biliary drainage

Start Smart…

  • Best guess (empirical) antibiotics
  • Intestinal source: “coliforms” and anaerobes
    • Cefuroxime & metronidazole (
37
Q

How are intraperitoneal abscesses treated?

A

Generally require drainage
“If there’s pus about…let it out!”

CT/ultrasound guided
Surgical (multilocular abscesses)
Combined with antimicrobial therapy

Clinical Pathology G (23 decks)

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