Septic peritonitis is a challenging problem to diagnose and treat in dogs and cats. Early diagnosis may improve survival as it will lead to quicker surgical resolution and elimination of the septic foci. Part of the challenge is that is that the physical examination only positively predicts those that require surgery 50% of the time (Walters, 2003).  Dr. Natashia Evans and Dr. Jayme Hoffberg gives the following tips to help diagnose septic peritonitis:

Tips for Diagnosing Septic Peritonitis in Dogs & Cats Based on Imaging Diagnostics:

  1. Presence of free gas on either radiographs or abdominal ultrasound. Free gas is most commonly found between the liver and diaphragm.  It is important to remember though that there can be free gas remaining after a recent abdominal surgery for up to 30 days.  Free gas occurs in septic peritonitis due to gas forming bacteria, penetrating wounds, or a rupture of a hollow viscous (such as the gastrointestinal tract).
  2. Identifiable cause on a radiograph or an ultrasound such as a mass, abscess or foreign body.

Tips for Diagnosing Septic Peritonitis in Dogs & Cats Based on Fluid Analysis:

  1. Compare peripheral blood glucose (BG) and abdominal fluid glucose levels. In septic cases, fluid glucose is lower than blood glucose due to utilization by bacteria. A difference of 20 mg/dL (abdominal fluid being LOWER than peripheral) warrants exploratory surgery. The samples must be drawn concurrently and analyzed immediately on a blood chemistry analyzer. We do not recommend using Point of Care analyzers such as AlphaTRAK as they are subject to inaccuracies. Blood to fluid glucose (BFG) difference >20 mg/dL showed 100% sensitivity and 100% specificity in dogs, 86% sensitivity and 100% specificity in cats (Bonczynski 2003).
  2. Compare peripheral lactate and abdominal fluid lactate levels. In septic cases, fluid lactate is higher than blood glucose due to production by bacteria. In pets with clinical signs of septic peritonitis, a difference of 2 mmol/L in Lactate (Abdominal fluid being HIGHER than peripheral lactate) warrants exploratory surgery with a sensitivity of 63% to 100% and a specificity of 100%. Lactates are NOT considered accurate in cats. (Bonczynski 2003, Levin 2004). If clinical signs are consistent with septic peritonitis and the lactate difference is >2 mmol/L, surgery should be recommended.
  3. Additionally, elevated lactate levels in the abdominal fluid alone can indicate a septic peritonitis Lactate > 2.5 mmol/L had a sensitivity of 100% and specificity of 91% in dogs. (Levin 2004).
  4. Evaluation of abdominal fluid is important to diagnose septic peritonitis when abdominal fluid to peripheral blood glucose (BG) and/or abdominal fluid to peripheral lactates is not helpful or equivocal. Septic abdominal fluids generally have increased neutrophils and macrophages, neutrophil degeneration, and free or phagocytized bacteria. However, you do NOT need to document intra or extracellular bacteria in the abdominal fluid to commit to a recommendation for emergent surgical exploratory.

We hope these tips for diagnosing septic peritonitis in dogs & cats help you.

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