Intra-abdominal%20infections Diagnosis

• Routine history, physical and laboratory exams usually identify patients with suspected intra-abdominal infections (IAI)

Community-acquired IAI (CA-IAI)

• Usually secondary to gastroduodenal perforation, ascending cholangitis, cholecystitis, appendicitis, colon diverticulitis with or without perforation, or pancreatitis
• Common pathogens involved are Enterobacteriaceae, Streptococcus spp, coliforms and anaerobes (especially Bacteroides fragilis and Escherichia coli)

Healthcare-associated IAI (HA-IAI)

• Usually secondary to leak or perforations from anastomosis or abscess from surgical site and/or wound infections
• Considered in the development or worsening of organ dysfunction in the days after abdominal surgery
• Range of pathogen involved is broader, which includes Enterobacteriaceae, Streptococcus spp, anaerobes, Enterococcus spp, Candida spp, or Pseudomonas aeruginosa
• Commonly involves at least 1 multidrug-resistant (MDR) organism, which needs the use of broad-spectrum antibiotics that is based on culture results and local antibiograms
• Community-onset HA-IAI includes patients with history of surgery or hospitalization within the past 90 days, or stayed in a care facility for a long time, used IV therapy/wound dressing at home or underwent outpatient hemodialysis or chemo/radiotherapy within the previous 30 days of the index infection
• Hospital-onset HA-IAI includes patients with a positive culture result obtained >48 hours after hospital admission or after initial source control

Uncomplicated IAI

• Infectious process involves only a single organ and does not extend to the peritoneum
  
  • Usually involves intramural inflammation of the gastrointestinal tract
• May progress to complicated infection if not properly treated
• Usually has low severity but may present as severe sepsis

Complicated IAI (cIAI)

• Infection that extends beyond the hollow viscus of origin into the peritoneal space and may be associated with peritonitis or abscess formation

• May provide the basis of decision regarding the need for intensive resuscitation or rehydration, need for diagnostic imaging procedures, timing of antibiotic therapy, and urgent need for an intervention
  
  • Patient with IAI usually presents with rapid onset of abdominal pain, loss of appetite, nausea, vomiting, bloating or obstipation, that may be accompanied with signs of inflammation (eg pain, tenderness, fever, tachycardia, tachypnea)
  • Hypotension and hypoperfusion signs (eg altered mental status, oliguria, lactic acidosis) indicate progress to severe sepsis
  • Abdominal rigidity is suggestive of peritonitis and need for urgent surgical intervention
• IAI should be considered in patients who have unreliable physical exam findings (eg patients with obtunded mental status, spinal cord injury, or who are immunosuppressed) and have evidence of undetermined infection

Gram Stain

• Helpful in patients with HA-IAI to determine co-infection with yeast
• Not recommended in patients with CA-IAI

Blood Culture

• Helpful in determining the length of therapy in immunocompromised or clinically toxic-appearing patients
• Blood cultures and peritoneal fluid direct examination for yeasts must be done in patients with HA-IAI and CA-IAI who are immunosuppressed and/or in septic shock
• Considered significant if the microbes isolated have established pathogenic potential or are present in ≥2 blood cultures

Aerobic or Anaerobic Culture from Site of Infection

• Specimens that will be collected from the site of infection should be at least 1 mL of fluid or tissue and is transported to the lab in an appropriate transport system
  
  • Regardless if it is a community-acquired or nosocomial peritonitis, samples from close suction drains and drainage systems should not be used as these yield uninterpretable results; results from chronic drains or fistulae should be interpreted carefully
• Considered significant if the microbes isolated are in moderate or heavy concentrations
• Recommended in patients with HA-IAI (intra-operative cultures), perforated appendicitis, other CA-IAI if the common community isolates (eg E coli) have 10-20% resistance to the widely used local antimicrobial regimen, and in patients who are at high risk especially those with prior antibiotic use
• Optional in patients with CA-IAI
  
  • Determines changes in resistance patterns of pathogens associated with CA-IAI and guides follow-up oral therapy
• Anaerobic cultures are not required for patients with CA-IAI if empiric antimicrobial therapy given has activity against anaerobic pathogens

Susceptibility Testing

• Recommended for species which are more likely to yield resistance (eg Pseudomonas, Proteus, Acinetobacter, Staphylococcus aureus, and Enterobacteriaceae with moderate-heavy growth)

Fine-needle Aspiration

• Image-guided, diagnostic, fine-needle aspiration can be performed for bacterial and fungal small (<3 cm) intra-abdominal collections and when diagnosis is in doubt

• For pediatric patients, non-irradiating imaging is preferred
• In patients with clear sign of diffuse peritonitis and in whom surgery is warranted, further diagnostic imaging is not recommended
  
  • Imaging may not also be required in a critically ill patient with a suspected peritonitis from a perforated organ if it would delay surgery
• Plain X-ray of the abdomen is usually the 1st imaging procedure requested in patients suggestive of IAI
  • Upright films may show free air under the diaphragm (most commonly on the right side), which indicates perforated viscus
• Computed tomography (CT) scan is the imaging modality of choice in stable adult patients who will not undergo immediate laparotomy
  
  • Will determine the presence and source of IAI
  • Also done in stable patients in whom postoperative peritonitis is suspected
• For unstable patients who do not need immediate laparotomy, abdominal ultrasound is the imaging procedure of choice
  
  • Patient’s discomfort, abdominal distension and bowel gas interference are the limitations of this test
  • 1st imaging test used in patients with suspected acute cholecystitis or cholangitis
• Diagnostic peritoneal lavage may be used in cIAI when neither CT scan nor abdominal ultrasound is available