Introduction

Peritonitis is an inflammation of the peritoneum from infected material in the abdominal cavity.  It is a serious but rare acute infection, which can lead rapidly to hypovolaemic shock and death.

Peritonitis is usually secondary to a perforated hollow viscus or to contamination after trauma.

Less common forms of peritonitis

Pathogenesis of peritonitis

Aetiology of peritonitis

Peritonitis is generally secondary to an underlying abdominal condition and management of peritonitis requires the management of this underlying condition. 

Community-acquired peritonitis is often polymicrobial and involves both aerobes and anaerobes.

Patient characteristics may provide some clue to the causative organism.  If the patient has been hospitalised previously, especially if they have received antibiotics, resistant organisms (such as Pseudomonas spp., or Acinetobacter spp.) or fungi may become important pathogens.

If ascites is present, Gram-positive cocci and aerobic Gram-negative bacilli are the most likely pathogens.  The origin of infection, eg. bladder, bowel or abscess, will also provide clues to the identity of the pathogen.

Diagnosis of peritonitis

Clinical

Patients with peritonitis present with:

• Severe and generalised abdominal pain
• Vomiting
• Pyrexia
• Rigid/board-like and tender abdomen
• No bowel sounds.

In some patients (eg. advanced age or immunosuppression) the signs are less severe, with diminished pain or a muted inflammatory response.  A high index of suspicion is required for diagnosis in these patients.

Laboratory investigation

• Blood culture: about 30% of patients have positive blood cultures.  The blood culture is often monomicrobial, while the infection in the peritoneal cavity is generally found to be polymicrobial.
• Culture of peritoneal cavity fluid (acquired at surgery or by needle aspiration) may allow rationalisation of antibiotic therapy.
• In spontaneous bacterial peritonitis, paracentesis allows diagnosis based on increased numbers of polymorphonuclear leukocytes (PMN) in ascitic fluid.

Imaging may be useful.

Management of peritonitis

Peritonitis is generally secondary to an underlying abdominal condition and management of peritonitis requires the management of this underlying condition.  Therefore correct antibiotic therapy for peritonitis depends on identification of the underlying condition. 

Management of peritonitis is with:

• Laparotomy/surgical debridement/drainage as required
• Systemic antibiotics
• Aggressive fluid administration
• Support of failing organs
• Nutrition.

Antibiotic rationale

Patient characteristics may provide some clue to the causative organism; for instance, if patients have been hospitalised for some time Pseudomonas spp. must be considered.  In addition, infection acquired in hospital is more likely to result from resistant/multiresistant pathogens.  If ascites is present, Gram-positive cocci and aerobic Gram-negative bacilli are the most likely pathogens.  The origin of infection, eg. bladder, bowel or abscess, will also provide clues to the identity of the pathogen.

Combination therapy is generally required.  In general only combination therapy provides the broad-spectrum activity necessary for polymicrobial infections and because the infection is potentially very serious, there may only be one chance for antibiotic treatment, which must have the maximum possible chance of success.  Finally, combination therapy may also reduce the chance of resistance developing. 

• It is mandatory that antibiotics provide coverage for Escherichia coli and other Gram-negative facultative anaerobes, and for Bacteroides spp. 
• If hospital-acquired infection is suspected, then coverage of multi-resistant Gram-negative pathogens ought to be considered. 
• The initial regimen below may select for Enterococcus spp.  If this occurs, the patient may initially improve and then worsen.  The addition of ampicillin or amoxicillin to this regimen provides coverage of Enterococcus spp.

Empirical therapy

• Initial therapy: a second-generation cephalosporin such as cefuroxime, plus metronidazole.
• If the patient’s condition deteriorates or the disease is initially serious, with a known or suspected bowel perforation, there are two options:
• The addition of ampicillin or amoxicillin to the above regimen to cover Enterococcus spp. 
  (= cefotaxime/ceftriaxone, plus metronidazole, plus ampicillin/amoxicillin)
• The use of gentamicin (to cover Enterobacteriaceae) plus ampicillin/amoxicillin (to cover Enterococcus spp.) plus metronidazole (to cover anaerobes).

If the condition is severe, consult your local microbiologist as therapy will depend on
local resistance patterns.

Intravenous therapy is required until gastrointestinal function is restored.

If the patient fails to improve after a week of treatment, then residual or recurrent abdominal infection should be suspected.

CAPD peritonitis

Introduction

Among patients on continuous ambulatory peritoneal dialysis (CAPD), peritonitis is common but is milder than other forms of peritonitis.  However, it is associated with catheter loss (and thus return to haemodialysis) and with considerable morbidity.

The prognosis of peritonitis in CAPD is generally favourable (<1% mortality).

Peritonitis in CAPD usually occurs 24–48 h after contamination and results from:

• Contamination with skin organisms when the bag/transfer set is changed
• Contamination occurring when the catheter is changed
• Infection, possibly subclinical, at the exit site of the catheter, or from colonisation of the catheter cuff or tunnel.

The infection rate is high: a suggested management target is no more than one episode of peritonitis every 18 months per patient. 

Aetiology of CAPD peritonitis

The most common causes of infection are:

• Staphylococcus epidermidis (the most common causative organism: normally associated with mild disease).

Other organisms are associated with more severe disease:

• Staphylococcus aureus
• Pseudomonas
• Streptococcus spp.
• Fungal peritonitis.

Diagnosis of CAPD peritonitis

Clinical

In CAPD patients the signs and symptoms of peritonitis include:

• Cloudy peritoneal effluent
• Abdominal pain
• Fever.

Laboratory diagnosis

• The presence of bacteria or fungi can be shown by culture or Gram stain of effluent. 
• Gram stain is positive in up to 40% of cases and correlates strongly with culture results.  Although it is only positive in a minority of cases, Gram stain is recommended because when positive it provides a rapid indication of unusual pathogens such as fungi or yeast and an indication of broad classes of organisms. 
• >100 white blood cells/mm³ in peritoneal effluent indicates a need for immediate antimicrobial therapy
  • The WBC count may be lower in patients on automated peritoneal dialysis (APD).

Management of CAPD peritonitis

In CAPD and automated peritoneal dialysis patients, prompt therapy of peritonitis is required.  Catheter removal may be needed.

Indications for catheter removal are: catheter or tunnel infections; fungal, tuberculous, persistent or relapsing peritonitis; bowel perforations; cuff erosion and protrusion; and post-transplant peritonitis.

• Patients should be advised to contact the renal unit immediately if they develop symptoms of peritonitis. 
• Intraperitoneal antibiotics can be administered via the dialysate, which increases local concentrations of the antibiotic and allows self-treatment.
• In severely ill patients, intravenous antibiotics or an intraperitoneal loading dose may be required.
• Vancomycin-containing regimens used to be the first choice for treatment, but recent guidelines recommend they should be avoided to reduce the incidence of vancomycin resistance.  Vancomycin still has a place in therapy, but should not be first-line treatment. 
• Aminoglycosides should also be avoided as first-line therapy where possible, to preserve residual renal function.
• Cephalosporins have the required broad-spectrum of action and a track record of effective use; they are still recommended.

Empirical therapy

The International Society for Peritoneal Dialysis updated guidelines (2000) recommend:

• Initial empirical treatment: a first-generation cephalosporin (such as cefazolin plus ceftazidime), both administered via the dialysate bag.

Adult peritoneal dialysis-related peritonitis treatment recommendations: 2000 update.

• Other regimens include intraperitoneal aminoglycosides, vancomycin or cephalosporins, alone or in combination.  Please consult your microbiologist for information regarding local policies.

The regimen can be adjusted once culture results have been obtained.  Consult your local microbiologist.

• If cultures prove negative, then re-investigation for mycobacteria or fungi is required, unless the patient is improving.  Catheter removal should be considered.
• If the causative organisms are found to be Staphylococcus aureus or Pseudomonas aeruginosa, a cuff infection is most probably present and therefore systemic antimicrobial therapy active against intracellular bacteria should be included in the treatment regimen.
• Fungal peritonitis can be treated with:
• Oral fluconazole plus oral or intraperitoneal 5-flucocytosine, for at least 10 days after catheter removal or for 4–6 weeks if the catheter is not removed. 
• Catheter removal is often required, although reinsertion is frequently possible.

Duration of treatment

Treatment should be continued for one week after clearing of the peritoneal effluent (usually total treatment of 10–14 days) or for one week after catheter removal. 

Adult peritoneal dialysis-related peritonitis treatment recommendations: 2000 update.

Antibiotic prophylaxis in CAPD

• Antimicrobial prophylaxis is not recommended on a continuing basis during dialysis. 

Indications for short-term prophylaxis:

• Short-term prophylaxis (single dose of amoxicillin) is recommended during extensive dental procedures
• Short-term administration of a first-generation cephalosporin can be used at catheter insertion
• Mupirocin used at the exit site or nasally may reduce exit-site infections. Treatment of exit-site infections may reduce the incidence of peritonitis
• Oral nystatin prophylaxis given at the same time as antibiotics for peritonitis or severe sepsis (but not exit-site infections) is effective in reducing the incidence of fungal peritonitis in CAPD.  

Persistent and relapsing peritonitis:

• There is no role for antibiotic prophylaxis
• Catheter removal is required in 10–20% of patients if there is no clinical response after 96 h of therapy, although replacement may be possible
• There may be an occult site of infection, such as an intra-abdominal abscess, and catheter removal should be considered in these cases, although future replacement may be possible.