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Complicated intra-abdominal infection
Definition
- Infections that spread beyond the hollow viscus of origin into the
peritoneal space and are associated with:
- abscess formation or
- peritonitis
- primary = spontaneous bacterial peritonitis
- arises without a breach in the peritoneal cavity or GI tract
- secondary
- occurs as a result of spillage of gut organisms through a
physical hole in the GI tract or through a necrotic gut wall
- may be community acquired or healthcare associated
- tertiary
- peritonitis in a critically ill patient which persists or
recurs at least 48 h after apparently adequate management of
primary or secondary peritonitis
Microbiology
Abscesses or secondary peritonitis
- health care associated intra-abdominal infection usually due to nosocomial
organisms particular to the site of the operation and specific hospital and
unit
- community acquired infections
- infections derived from stomach, duodenum, biliary system and proximal
small bowel:
- Gram positive and Gram negative aerobic and facultative bacteria
- distal small bowel:
- Gram negative facultative and aerobic bacteria
- Anaerobes
- large bowel:
- Facultative and obligate anaerobic bacteria
- Streptococi and enterococci commonly present
Tertiary peritonitis
- coagulase negative staphylococci
- Pseudomonas
- Candida
- Enterococci
Clinical features
- difficult to diagnose in the critically ill patient because history is
usually unobtainable and physical signs usually masked by decreased
conscious level
- consider diagnosis in the appropriate clinical setting in patients with
otherwise unexplained signs of sepsis or organ dysfunction:
- recent abdominal surgery
- source of arterial emboli
- peripheral vascular disease
- thrombotic disorder
- recent arteriography
- history of reduced splanchnic blood flow (eg use of vasopressors or
prolonged shock)
- unexpected shortness of breath or supraventricular tachycardia
occurring 3-4 days after an abdominal operation, new onset renal dysfunction
or elevated bilirubin or transaminases should all raise suspicion of
intra-abdominal infection
Investigations
Microbiological
- Blood cultures
- often negative
- polymicrobial or anaerobic bacteraemia should raise possibility of
anaerobic infection
- Community acquired infections: Gram stain of no value
- Healthcare associated infections: Gram stain may be valuable in defining
need for specific therapy S.aureus or Enterococcus spp.
Radiological
- Definitive diagnostic approach to intra-abdominal infection
AXR
- look for free gas, bowel obstruction, or subtle signs of intestinal
ischaemia
- water-soluble contrast studies can show leaks
- injection of contrast into drains, fistulae or sinus tracts may help
demonstrate anatomy of complex infectios and help monitor adequacy of
abscess drainage
Ultrasound
- advantage of being portable and almost risk-free
- useful for:
- identifying abscesses and fluid collections
- guidance of percutaneous drainage procedures
- detection of free fluid
- evaluation of biliary tree
- disadvantages:
- operator dependent
- difficult to perform in patients who have abdominal dressings or
paralytic ileus
CT abdomen
- with use of IV and oral or rectal contrast most causes of secondary
peritonitis can be readily diagnosed
- requires movement of potentially unstable patient out of ICU
- relative contraindications:
- renal dysfunction: contrast may aggravate renal dysfunction
- paralytic ileus
- a negative CT generally indicates a very low probability of a process that
can be reversed by surgical intervention, however bowel ischaemia cannot be
excluded, particularly in the early stages
Invasive investigations in ICU
- judicious probing of surgical wounds with sterile culture swab or gloved
finger can often identify collections of infected material immediately
adjacent to incision
- diagnostic peritoneal lavage
- may reveal bacteria, white cells, bile or intestinal contents
- bloody lavage return suggests acute intestinal ischaemia
- bedside laparoscopy
- difficult
- experience in critically ill patients largely anecdotal
Management
- physiological resuscitation
- systemic antibiotics
- source control
Antibacterials
Should be administered as soon as infection is suspected and preferably
before surgical intervention (to minimize the risk of surgical wound infection.
Choice of antibacterials for community acquired infection
- should be active against enteric Gram negative aerobic and facultative
bacilli and ß-lactam susceptible Gram positive cocci
- for distal small bowel and colon-derived infections antibacterials should
cover anaerobes. Same recommendation also applies to more proximal GI
perforations when obstruction is present
- avoid agents used to treat nosocomial infection in the ICU, except for
high risk patients
- inclusion of antibacterials that cover enterococcal infections provides no
benefit in terms of outcome for patients with community acquired infections
- suitable regimes include:
- cefazolin or cefuroxime plus metronidazole
- metronidazole plus quinolone (eg moxifloxacin or gatifloxacin)
- high risk patients should be given antibacterials with a wider spectrum of
activity
- risk factors:
- higher APACHE II
- poor nutritional status
- significant cardiovascular disease
- inability to obtain adequate source control
- immunosuppression
- suitable regimes include:
Choice of antibacterials for healthcare associated infection
- more resistant flora routinely encountered
- organisms seen are similar to those seen in other nosocomial infections
- treatment should be based on knowledge of local nosocomial flora and their
resistance patterns
- agents which cover enterococci should be used when enterococci are
isolated from patients with healthcare associated infections
- role of antibiotics in tertiary peritonitis is poorly defined
- little evidence that they significantly alter outcome
- some recommend the use of narrow spectrum agents based on results of
culture and sensitivity and avoidance of agents with anti-anaerobic
activity
- there are some data which suggest that use of antibiotics with
anti-anaerobic activity increases gut colonization with Candida
and vancomycin resistant Enterococci.
Duration of therapy
- No more that 24 h for:
- bowel injuries due to penetrating, blunt or iatrogenic trauma that are
repaired within 12 h
- intraoperative contamination of operative field by enteric contents
- acute perforations of stomach, duodenum and proximal jejunum in
absence of antacid therapy or malignancy
- For patients with established infections:
- until resolution of signs of infection occurs. This assessment should
be based on signs of sepsis and return of GI function
- if source control is adequate the role of antibiotics is largely
adjuvant and the course can usually be restricted to 5-7 days
- further investigation is indicated or patients with persistent or
recurrent clinical evidence of intra-abdominal infection after 5-7 days
of therapy
Source control
Physical measures to eradicated focus of infection, prevent on-going
contamination and ultimately to restore optimal anatomy and function
- drainage
- debridement
- definitive management
Successful source control and antibiotic management is associated with
resolution of clinical features of systemic inflammation and reversal of organ
dysfunction. Progression or failure of resolution of organ dysfunction suggests
persistence of the disease and the need for further intervention
Drainage
- formation of an abscess isolates infection from surrounding sterile
tissues but has disadvantage of preventing influx of host immune cells and
antibiotics
- drainage converts to a controlled sinus or fistula
- percutaneous ultrasound or CT guided drainage is initial intervention of
choice for management of localized, radiologically defined infectious foci
- can also be used as a temporizing measure eg to decompress infected
retroperitoneal collections in patients with necrotizing pancreatitis so
operative intervention can be delayed until it is safer
- indications for surgical drainage:
- failure of percutaneous drainage
- collections with a significant solid tissue component requiring
debridement
- simultaneous managment of a source of ongoing contamination
- when local peritoneal defences have not contained the infectious
focus, resulting in generalized peritonitis
Debridement
- in contrast to drainage which removes the liquid component of an
infection, debridement is the physical removal of infected or necrotic solid
removal
- debridement less frequently required in patients with intra-abdominal
infection
- main indications in this setting:
- intestinal infarction
- infected peripancreatic necrosis
- decision of when to operate relates to relative risks and benefits. Thus
the benefit of early excision of necrotic bowel vastly outweighs the risks.
In contrast, the bacterial burden in infected retroperitoneal necrosis is
lower and the organisms sequestered in the necrotic tissue are less able to
gain access to the circulation. In addition early exploration is difficult
because of poor demarcation between viable and non viable tissue. As a
result there is a trend to delayed rather than immediate intervention
Further reading
Infectious
Diseases Society of America Guidelines for the selection of anti-infective
agents for complicated intra-abdominal infections. (Solomkin JS et al. Clin
Infect Dis, 2003;37:997-1005)
Marshall JC, Innes M. Intensive care unit management of
intra-abdominal infection. Crit Care Med, 2003; 31(8):2228-37
Potential conflict of interest
The Dept of Anaesthesia & Intensive Care has received
educational, research or travel grants from AstraZeneca, Daiichi
Pharmaceuticals, Merck Sharp & Dohme, Pfizer and Wyeth.
Document created April 2004 |
