Intra-abdominal infections Flashcards
Definition of intra-abdominal infection?
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
Why is the proximal small intestine relatively free of microorganisms? What ones are there?
Growth inhibited by bile
A few aerobic bacteria and Candida spp.
How many organisms are there normally per gram?
10^9-10^11
What is the normally the percentage of anaerobic bacteria?
95-99%
What are the normal types of aerobic bacteria in the large intestine?
Enterobacteriaceae (enteric Gram-negative bacilli, coliforms)
Gram-positive cocci (mainly enterococci)
What are sources of gastrointestinal infection?
Gastrointestinal contents
Blood
External
What are the 3 mechanisms of intra-abdominal infection?
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
How does translocation across a wall occur?
Perforation
- Perforated appendix, perforated ulcer, perforated diverticulum, malignancy
Loss of integrity
- Ischaemia, strangulation
Surgery
- Seeding at operation, anastomotic leak
How does translocation along a lumen occur?
Blockage
- Cholecystitis, cholangitis, hepatic abscess
Iatrogenic
- Instrumentation (e.g. ERCP)
What are the clinical features of a perforated appendix?
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
What are diverticula and what can their complications include?
Herniations of mucosa/submucosa through muscular layer
- Sigmoid and descending colon
Asymptomatic diverticula are very common
- 50% > 70 yrs
Complications
- Diverticulitis
- Perforation
- Pericolic abscess
Why can bowel cancer cause intra-abdominal infections?
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
What causes ischaemia of the bowel?
Interruption of intestinal blood supply
- Strangulation
- Arterial occlusion
- Post-operative
e. g. aneurysm repair
Gut wall loses structural integrity
Allows translocation of luminal contents
What are the features of post-operative infection?
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
What is cholecystitis?
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
How does cholecystitis present?
Fever, right upper quadrant pain, mild jaundice (CBD remains patent)
What is emphysematous cholecystitis?
Intramural gas in gallbladder wall
What is empyema of the gallbladder?
Complication of cholecystitis
Frank pus in gallbladder
Presentation is as for cholecystitis but septic presentation
- Severe pain
- High fever
- Chills and rigors
What is cholangitis and what causes it?
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)
How does cholangitis present?
Fever (rigors), jaundice and right upper quadrant pain
Presentation may be non-specific
What are the routes of infection of pyogenic liver abscesses?
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
What are intra-peritoneal abscesses?
Localised area of peritonitis with build-up of pus
- Subphrenic, subhepatic, paracolic, pelvic etc.
What are the predisposing factors for intra-peritoneal abscess?
Perforation
- Peptic ulcer
- Perforated appendix
- Perforated diverticulum
Cholecystitis
Mesenteric ischemia/bowel infarction
Pancreatitis/pancreatic necrosis
Penetrating trauma
Postoperative anastomotic leak
How does a non-specific intra-peritoneal abscess present clinically?
Sweating, anorexia, wasting
High swinging pyrexia
How does a subphrenic abscess present clinically?
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.”
How does a pelvic abscess present?
Urinary frequency
Tenesmus
Name some other conditions that can cause intra-abdominal infections?
Spontaneous bacterial peritonitis (SBP)
- Infected ascitic fluid
Pancreatic and splenic abscesses
Amoebic abscess
- Entamoeba histolytica
Hydatid cyst
- Echinococcus granulosus
Ileo-caecal tuberculosis
- Mycobacterium tuberculosis
Name some aerobic gram-negative bacilli
Enterobacteriaceae (coliforms)
- Predominantly E. coli
- Also Enterobacter, Citrobacter, Klebsiella, Proteus, Serratia, spp. etc.
Pseudomonas spp.
Name some Anaerobic Gram-negative bacilli
Bacteroides spp., Prevotella spp.
Name some Aerobic Gram-positive cocci
Enterococcus spp.
Occasionally milleri-group streptococci (S. anginosus/constellatus group)
Name an anaerobic gram-positive bacilli
Clostridium spp
Hepatobiliary tract infections involve GI flora from what level?
usually involve lower GI flora, despite duodenal origin
What blood tests may be done when intra-abdominal infection is suspected?
Full blood count: neutrophilia/neutropenia
C-reactive protein: raised
Liver function tests: abnormal in hepatobiliary disease
What types of imaging would be used for suspected intra-abdominal infections and what would you be looking for?
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)
What other microbiological investigations could you perform?
Samples to test
- Blood
- Peritoneal fluid
- Ultrasound/CT guided drainage fluid
Microscopy, culture and sensitivity testing
What are the principals of antimicrobial therapy for intra-abdominal infections?
Treat underlying condition
- e.g. resection, anastomosis, abscess drainage, biliary drainage
Start Smart…
- Best guess (empirical) antibiotics
- Intestinal source: “coliforms” and anaerobes
- Cefuroxime & metronidazole (
How are intraperitoneal abscesses treated?
Generally require drainage
“If there’s pus about…let it out!”
CT/ultrasound guided
Surgical (multilocular abscesses)
Combined with antimicrobial therapy
