Approach

IAA treatment is summarised by two steps: source control and effective antimicrobial therapy.[27] The source is usually controlled by either surgical or percutaneous drainage to completely evacuate the abscess cavity. Adequate source control, in addition to early appropriate effective antimicrobial therapy, is usually sufficient.

When the leak is large and therefore not contained, further surgical treatment is warranted to wash out the abdominal cavity and establish source control, usually by repairing the perforation or diverting the bowel proximal to the leak. Inadequate source control at the time of the initial surgery is associated with an increased mortality.[28]

Assessing risk of adverse outcome and treatment failure

  • Assess phenotypic and physiological factors:

    • Signs of sepsis: patients may present with shock; sepsis may also occur early after drainage of an IAA. Sepsis treatment guidelines have been produced by the Surviving Sepsis Campaign and remain the most widely accepted standards.[29] Current best practice is based upon evidence for care bundles in sepsis.[29][30][31][32]

    • Extremes of age

    • Comorbidities

    • Extent of abdominal infection and adequacy of source control

    • Presence of resistant or opportunistic pathogen.

  • Characterise patients as either low or high risk for treatment failure or mortality.

  • Assess for community-acquired or health care-acquired infection.

  • Patients with Surviving Sepsis Campaign criteria for sepsis or septic shock, and those with APACHE II score greater than or equal to 10, are at higher risk.

  • Prolonged length of hospitalisation prior to surgery for intra-abdominal infection.

  • Patients with diffuse peritonitis.

  • Patients with delayed source control.[2]

Percutaneous drainage

Percutaneous drainage is a successful modality in most cases.[33] For simple abscesses that are not associated with suspected malignancy or large anastomotic leaks, percutaneous drainage, if feasible, could be the first-line therapy. Percutaneous drainage can be performed using guidance from either ultrasound or computed tomography (CT) scan.[34] Although very useful where there are only one or two IAA, percutaneous drainage is limited when the trajectory to the abscess requires cross-contaminating a different cavity, such as the pleura, or when the source of contamination is not sufficiently controlled, such as a large anastomotic breakdown.

Percutaneous drainage can be used as part of a staged surgical procedure such as in diverticulitis, Crohn's disease, or appendicitis.[35] The overall success rate of staged surgical procedures using percutaneous catheter drainage is about 76%, and as high as 94% in appendicitis.[36] Appendiceal abscess is usually managed with percutaneous drainage, which is a sufficient treatment in many cases. Abscesses related to Crohn’s disease can often be managed initially with antibiotics and percutaneous drainage, thus avoiding emergency operations and multi-stage procedures. In highly selected cases, surgery might be avoided entirely.[37]

In one multi-centre prospective study, a pancreatic origin of the abscess or positive yeast culture was a negative predictor of a successful percutaneous outcome, and post-operative abscesses were a favourable indicator of this outcome.[36] Although open surgical drainage may seem to have a higher mortality, this is likely to be due to patient selection bias.[14] In one large series of 95 patients with 107 abscesses, image-guided percutaneous drainage was performed with ultrasound in 71 procedures and with CT scan guidance in 36 procedures.[33] Immediate technical success was achieved in 107 of 107 fluid collections with the use of 8F to 14F pigtail drainage catheters, and no major complications occurred. Overall, the drainage catheter was left in place for a mean of 14.2 days. In 9 of 107 cases, percutaneous drainage was unable to resolve the fluid collection. Although percutaneous drainage is less invasive than surgery, this procedure has its own disadvantages and morbidities. Complications of percutaneous drainage include displacement or obstruction of the catheter, post-procedural septicaemia, and insufficient drainage.[33] Other complications may include bleeding and inadvertent injury to surrounding structures.

The catheter can be removed when clinical findings disappear and drainage is <10 mL in 24 hours. Before removing the catheter, it should be ensured that cessation of drainage is not due to catheter blockage.[38]

Surgical source control

The surgical procedure depends on the cause of the IAA.[27]

  • In the case of a gastric or duodenal perforation, repair with a Graham patch with unroofing and drainage of the associated abscess may suffice.

  • A small-bowel perforation may require a primary repair or re-section, along with either a primary anastomosis or, at times, a double barrel ostomy.

  • Diverticulitis may require resection of the diseased colon and either end colostomy (a Hartmann's procedure) or primary anastomosis with or without diverting ileostomy.[39] Laparoscopic lavage with drainage has also been reported to be feasible in patients with purulent peritonitis, but is controversial as trials have shown conflicting results.[40][41][42]

  • Colonic anastomotic leaks may be treated with proximal diversion and drainage, without taking down the anastomosis.[43] When anastomotic leaks occur, the clinical picture usually dictates the course: a patient in septic shock should be resuscitated, then re-explored to determine where the leaking anastomosis can be taken down, and a proximal diversion should be performed. A single operation may not sufficiently control the source, and a 2-stage or multi-stage operation may be required. The presence of haemodynamic instability may contraindicate re-establishing bowel continuity, and a second laparotomy is usually planned within 24 to 48 hours. Negative pressure wound therapy can be considered if the abdomen is left open.[44]

Antimicrobial therapy selection

Early parenteral empirical antimicrobial therapy is critically important in treating IAA. Appropriate antimicrobial therapy is defined as the use of an antimicrobial that is effective against all of the pathogenic organisms isolated from the IAA. In patients with sepsis or septic shock, parenteral empirical antibiotics with broad-spectrum coverage should be initiated immediately after the diagnosis is made, as outcome worsens with each hour delay of antimicrobial therapy.[45] See Sepsis in Adults (Management Approach).

Two meta-analyses have demonstrated reduced short term mortality using an (off-label) extended-duration infusion of beta-lactams after the initial bolus.[46][47]

Appropriate cultures should be obtained before initiating antibiotic therapy, but should not prevent prompt administration of antimicrobial therapy.[2][29] Antibiotics should be given before surgical or percutaneous drainage.

The frequently isolated pathogens in intra-abdominal infections are as follows.

  • Gram-negative bacteria such as Escherichia coli, Enterobacter, Klebsiella, Proteus, or Pseudomonas.

  • Gram-positive bacteria such as Streptococcus, Staphylococcus aureus, or Enterococcus.

  • Anaerobes such as Bacteroides and Clostridium. The most prevalent anaerobic organism in intra-abdominal infections is Bacteroides fragilis, likely present in one third to one half of these infections.

  • Candida. The incidence of Candida infections depends on the presence of predisposing factors such as immunodeficiency, prior antimicrobial treatment, and peritoneal dialysis. It is more common in tertiary peritonitis (recurrent intra-abdominal infection after initial surgical and antimicrobial therapy of secondary bacterial peritonitis) and in abscesses related to duodenal pathology.

The breadth of the empirical coverage for these pathogens can depend upon the severity of illness, medical comorbidities, and adequacy of source control.

Non-high-risk patients

Non-high-risk patients with mild-to-moderate severity community-acquired IAA can be treated with either single-agent (e.g., ertapenem or moxifloxacin) or combination (e.g., metronidazole plus a cephalosporin or a quinolone) regimens, all of which are equally effective.[2]

Empirical antibiotics should cover gram-negative aerobic and facultative bacilli, and enteric gram-positive streptococci.[2] In the presence of distal small bowel, appendiceal, colonic, and proximal gastrointestinal perforations with obstruction or paralytic ileus, these antibiotics should be active against obligate anaerobic bacilli.[2]

Ampicillin/sulbactam, and cefotetan and clindamycin, should not be used due to the resistance of E coli and Bacteroides fragilis to these antibiotics, respectively.[2]

Patients may be switched to targeted antibiotic therapy once culture results are available.

High-risk patients

High-risk patients, or those with severe community-acquired IAA, should be started on broad-spectrum antimicrobial therapy with coverage of possible multi-drug-resistant gram-negative bacteria, including Pseudomonas aeruginosa, and then commit to de-escalation of antimicrobial therapy once the culture and susceptibility results are available. Specific decisions regarding optimal antimicrobial therapy should be based, in part, on local antibiograms and knowledge of common organisms in the hospital or community. A carbapenem or piperacillin/tazobactam should be used as a single-agent therapy; if combination therapy is desired, metronidazole should be combined with a cephalosporin.[2]

Empirical coverage of Enterococcus should be considered in these patients. Coverage of methicillin-resistant Staphylococcus aureus (MRSA) and Candida is only recommended if there is evidence of these infections.[2]

In adult patients with health care-associated complicated intra-abdominal infection, to achieve empirical coverage of the likely aetiological pathogens, multi-drug regimens, including broad-spectrum agents with activity against gram-negative aerobic and facultative bacilli, should be used.[2]

A carbapenem, piperacillin/tazobactam, a cephalosporin, or an aminoglycoside is recommended with metronidazole. Empirical anti-enterococcal therapy (e.g., piperacillin/tazobactam) against Enterococcus faecalis is recommended, especially for patients with post-operative infection or prosthetic intravascular materials, those who have previously received cephalosporins or other anti-enterococcal antibiotics, and for immunocompromised patients.[2]

Multi-drug-resistant pathogens are becoming an increasing concern. Vancomycin-resistant enterococci (VRE) are emerging pathogens that are resistant to many standard antibiotics. Data on the efficacy and safety of specific antimicrobials are limited, particularly with regard to the treatment of intra-abdominal infections. Linezolid is approved for the treatment of VRE infections; daptomycin and tigecycline may also be used.[2] Other antimicrobials are on the horizon but have not yet been approved.[48][49]

Adjunctive vancomycin for MRSA coverage is indicated in patients known to be colonised with MRSA or those at risk of MRSA infection because of prior treatment failure or significant antibiotic exposure.[2]

Other multi-drug-resistant organisms include gram-negative bacilli producing extended-spectrum beta-lactamase (ESBL). Carbapenems are the first-line option for treating ESBL bacteria, and ertapenem may be preferred for community-acquired infections.[50]

Other options are available depending upon the susceptibility of the strain. Development of new drugs is important given the emergence of carbapenem-resistant Enterobacteriaceae (CRE). Options for treatment include, but are not limited to, colistimethate (colistin) and tigecycline. Ceftazidime/avibactam has been approved in some countries, including the US, for the treatment of complicated intra-abdominal infections when used in combination with metronidazole. It is recommended for higher-risk patients with strongly suspected or proven infection with Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacteriaceae, for which other agents are not suitable.[2]

Antifungal therapy is only recommended if Candida is grown from intra-abdominal cultures. C albicans should be treated with fluconazole, while an echinocandin should be used for fluconazole-resistant Candida species and in critically ill patients.[2]

Duration of antimicrobial therapy

Duration of antimicrobial therapy depends on the adequacy of source control and the patient's response to therapy (i.e., resolution of all signs and symptoms of infection, such as fever, leukocytosis, and abdominal pain, and resolution of the IAA by repeat diagnostic imaging).

If the patient is not responding to empirical broad-spectrum antimicrobial therapy, diagnostic imaging and cultures should be repeated, and changing the antimicrobial management considered.

A successful trial of shorter-duration antimicrobial therapy has highlighted the importance of source control. One multi-centre randomised trial compared the duration of antimicrobials chosen based on resolution of clinical signs and symptoms of infection versus 4 days after source control for complicated intra-abdominal infections. The study found that patients receiving 4 days of antimicrobials had a shorter duration of therapy and had no difference in the composite outcome of surgical site infection, recurrent intra-abdominal infection, and death within 30 days.[51]

Consider limiting antimicrobial therapy to 7 days in patients with secondary bacteraemia due to intra-abdominal infection, who have undergone adequate source control and are no longer bacteraemic.[2]

Consideration should be given to limiting antibiotic therapy to 5 to 7 days in patients in whom a definitive source control procedure cannot be performed.[2] In those who demonstrate persistent clinical signs of infection (fever, leukocytosis, changes in bowel function) after 5 to 7 days of antibiotics, reassessment of source control should be considered.[2]

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