(24) Intra-abdominal infections Flashcards
What is the definition of an intra-abdominal infection?
Presence of micro-organisms in normally sterile sites within the abdominal cavity e.g. peritoneal cavity, hepatobiliary tree
Why is gastroenteritis NOT classed as an intra-abdominal infection?
Because the bowel lumen is a non-sterile site
Describe the normal flora of the stomach
Stomach considered to be sterile
Describe the normal flora of the proximal small intestine
Relatively free of microorganisms
- growth inhibited by bile
- a few aerobic bacteria and candida spp.
Describe the normal flora of the distal small intestine
Reflects that of the large intestine
Describe the normal flora of the large intestine
10^9-10^11 organisms/gram
Mainly anaerobic bacteria (95-99%)
Some aerobic bacteria eg.
- enterobacteriaceae (enteric gram-negative bacili, coliforms)
- gram-positive cocci (mainly enterococci)
Give 3 sources of intra-abdominal infection
- gastrointestinal contents
- blood
- external
Give 3 mechanisms of intra-abdominal infection
- translocation of microorganisms from gastrointestinal tract lumen to peritoneal cavity
- translocation of microorganisms along a lumen
- translocation of microorganisms from an extra-intestinal source
When there is translocation of microorganisms from GIT lumen to peritoneal cavity, what is the infection called?
Intraperitoneal infection
When there is translocation of microorganisms along a lumen, what infection could be caused?
Biliary tract/hepatobiliary infection
Give and example of when there could be translocation of microorganisms from an extra-intestinal source
- penetrating trauma
- haematogenous spread
What might allow translocation across a wall?
- perforation
- loss of integrity
- surgery
Perforation might allow translocation across a wall. Give example of perforation
- perforated appendix
- perforated ulcer
- perforated diverticulum
- malignancy
Loss of integrity might allow translocation across a wall. What might cause loss of integrity?
- ischaemia
- strangulation
What might cause translocation across a wall during surgery?
- seeding at operation
- anastomotic leak
What might allow translocation along a lumen?
- blockage (cholecystitis, cholangitis, hepatic abscess)
- iatrogenic (instrumentation eg. ERCP)
Perforated appendix (allowing translocation across a wall) is a disease of who?
Mainly children and young adults
How might the lumen of the vermiform appendix become obstructed?
- lymphoid hyperplasia
- faecal obstruction
What does obstruction of the lumen of the vermiform appendix lead to?
Stagnation of luminal contents, bacterial growth and recruitment of inflammatory cells
How might an obstructed lumen of appendix lead to perforation of the appendix?
- build up of intraluminal pressure may result in perforation
- escape of luminal contents into peritoneal cavity is “peritonitis”
What are the symptoms of perforated appendix?
- severe, generalised pain
- shock
- may localise to form “appendix mass” - inflamed appendix with adherent covering of omentum and small bowel
Describe an example case of perforated appendix
- 16 year old female
- short history of lower right sided abdominal pain
- presented with temperature 38 and collapse
- blood cultures grew E. coli and bactericides fragilis
- perforated appendix found at operation
- surgery: appendicectomy
- antibiotics: cefuroxime and metronidazole for 5 days
What is a diverticulum?
Herniation of mucosa/submucosa through muscular layer (sigmoid and descending colon)
How common are asymptomatic diverticula?
Very common
50% > 70 years
Give some potential complications of diverticula?
- diverticulitis
- perforation
- pericolic abscess
Is infection a complication of bowel cancer?
Intraperitoneal and/or bloodstream infection is an infrequent complication of bowel cancer
(especially associated with clostridium septicum and streptococcus gallolyticus - formerly S. bovid - blood stream infection)
How is intraperitoneal infection a complication of bowel cancer?
Presumably caused by loss of bowel wall integrity due to abnormal malignant tissue
Intraperitoneal infection may follow symptoms consistent with bowel malignancy such as..
- weight loss
- alteration of bowel habit
- blood in stool
etc
Ischaemia is caused by interruption of intestinal blood supply which may be caused by what?
- strangulation
- arterial occlusion
- post-operative eg. aneurysm repair
What may happen with ischaemia?
- gut wall loses structural integrity
- allows translocation of luminal contents
What 4 things may cause post-operative infection?
- seeding at operation
- anastomotic leak
- acute infection (abdo pain and tenderness, shock)
- intraperitoneal abscess (walled-off abscess, more indolent condition)
How is the incidence of seeding at operation reduced?
- bowel preparation
- prophylactic antibiotics
What is cholecystitis?
Inflammation of the gallbladder wall
- chemical inflammation
- bacterial infection may be cause or result of cholecystitis (cultures positive in 50-75% of cases)
Cholecystitis is associated with obstruction of the cystic duct. What is the cause of this?
Gall stones (90%)
Other causes =
- malignancy
- surgery
- parasitic worms
Very occasionally no obstruction
How does cholecystitis present?
- fever
- right upper quadrant pain
- mild jaundice (common bile duct remains patient)
What is emphysematous cholecystitis?
Acute infection of the gallbladder wall caused by gas-forming organisms (eg, Clostridium or Escherichia coli)
(intramural gas in gallbladder wall)
What is empyema of the gallbladder?
- a complication of cholecystitis
- frank pus in gallbladder
What is the typical presentation of empyema of the gallbladder/?
As for cholecystitis but septic presentation
- severe pain
- high fever
- chills and rigors
What is cholangitis?
Inflammation/infection of the biliary tree (hepatic and common bile ducts)
What are the causes of cholangitis?
Same causes as cholecystitis
- mainly obstruction of common bile duct
- can follow instrumentation (e.g. ERCP)
How does cholangitis present?
- fever (rigors)
- jaundice
- right upper quadrant pain
- presentation may be non-specific
What is a pyogenic liver abscess?
A pus-filled area in the liver.
What are the possible routes of infection causing a pyogenic liver abscess?
- biliary obstruction
- direct spread from other intra-abdominal infections
- haematogenous
- penetrating trauma
- idiopathic
Haematogenic spread is a possible route of infection causing a pyogenic liver abscess. What blood vessels may be involved?
- from mesenteric infection via hepatic portal vein
- from systemic intravascular infection via hepatic artery
What is an intra-peritoneal abscess?
Localised area of peritonitis with build-up of pus
- subphrenic
- subhepatic
- paracolic
- pelvic
etc
What are the predisposing factors to intra-periotneal abscess?
- perforation (peptic ulcer, perforated appendix, perforated diverticulum)
- cholecystitis
- mesenteric ischaemia/bowel infarction
- pancreatitis/pancreatic necrosis
- penetrating trauma
- postoperative anastomotic leak
Intra-peritoneal abscess may be a late complication. What does this mean?
Appears several months after predisposing factor
What are the non-specific symptoms of intra-peritoneal abscess?
- sweating
- anorexia
- wasting
- high swinging pyrexia
What are the specific symptoms of subphrenic abscess?
- pain in shoulder on affected side
- persistent hiccup
- intercostal tenderness
- apparent hepatomegaly (liver displaced downwards)
- ipsilateral lung collapse with pleural effusion)
- pus under the diaphragm
What are the main specific symptoms of pelvic abscess?
- urinary frequency
- tenesmus
Give 5 other intra-peritoneal conditions
- spontaneous bacterial peritonitis (SBP)
- pancreatic and splenic abscesses
- amoebic abscess
- hydatid cyst
- ileo-caecal tuberculosis
What is spontaneous bacterial peritonitis (SBP)?
Bacterial infection in the peritoneum causing peritonitis, despite the absence of an obvious source for the infection.
It occurs almost exclusively in people with portal hypertension
infected ascitic fluid
What is amoebic abscess caused by?
Entamoeba histolytica
What is hydatid cyst caused by?
Echinococcus granulosus
What is ileo-caecal tuberculosis caused by?
Mycobacterium tuberculosis
Give examples of aerobic gram-negative bacilli that can cause these infections
Enterobacteriaceae (coliforms)
- predominantly E.coli (also enterobacter, citrobacter, klebsiella, proteus, serratia spp. etc)
Pseudomonas spp.
Give examples of anaerobic gram-negative bacilli that can cause these infections
Bacteriodes spp.
Prevotella spp.
Give examples of aerobic gram-positive cocci that can cause these infections
Enterococcus spp.
Occasionally milleri-group streptococci (S. anginosus, constellatus group)
Give examples of anaerobic gram-positve bacilli
Clostridium spp.
Liver abscesses are usually caused by which microorganisms?
Usually polymicrobial
- may be “sterile” (contain hard-to-grow anaerobes)
- may be other associated abscesses (eg. brain)
Infections in the liver region may be secondary to what?
Haematogenous spread or trauma and therefore may not involve GI flora
Hepatobiliary tract infections usually involve which flora?
Lower GI flora, despite duodenal origin
How do you diagnose intra-peritoneal infections? (briefly)
- history
- examination
- investigations (blood tests, imaging, microbiological)
Which blood tests would you do if you suspect intra-peritoneal infection?
- full blood count (neutrophilia, neutropenia)
- C-reactive protein (raised)
- liver function tests (abnormal in hepatobiliary disease)
What 3 types of imaging would you do in intra-peritoneal infection?
- chest X-ray
- abdominal ultrasound
- abdominal CT scan
What might you see on a chest X-ray in intra-peritoneal infection?
- consolidation
- pleural effusion adjacent to infected area eg. subphrenic abscess
What might you see on abdominal ultrasound in intra-peritoneal infection?
- abdominal masses
- free fluid
- dilated bile ducts
Why might you use an abdominal CT scan rather than/as well as an ultrasound?
Higher definition than ultrasound
What is involved in microbiological investigations?
Samples to test =
- blood
- peritoneal fluid
- ultrasound/CT guided fluid drainage
Tests =
- microscopy
- culture
- sensitivity testing
How would you treat intra-abdominal infections (first step)?
Treat underlying condition eg.
- resection
- anastomosis
- abscess drainage
- biliary drainage
When using antibiotic therapy, you should “start smart…and then focus..”. Which antibiotics should you use first if the infection has an intestinal source?
- best guess (empirical antibiotics)
If intestinal source: “coliforms” and anaerobes
- cefuroxime and metronidazole (65 years)
- take into account previous microbiology results
When using antibiotic therapy, you should “start smart…and then focus..”. Which antibiotics should you use first if the infection has an extra intestinal source?
- best guess (empirical) antibiotics
If extra intestinal source: different organisms
- antibiotic choice will depend on source of infection
When using antibiotic therapy, you should “start smart…and then focus..”. What should you use after the best guess (empirical) antibiotics?
Narrowest possible spectrum based on culture results
When should you do an antibiotic oral switch?
After 48 hours apyrexial with normal white cell count
Do intra-peritoneal abscesses generally require drainage?
Yes
“if there’s pus about…let it out!”
How would you drain pus from an intra-peritoneal abscess?
- CT/ultrasound guided
- surgical (multiocular abscesses)
- combined with antimicrobial therapy
