Peritonitis - Cats and Dogs

Description

Peritonitis is defined as inflammation of the peritoneum. The inflammatory response involves vasodilation, exudation of protein-rich fluid, cellular infiltration, pain and, chronically, formation of fibrous adhesion. The disease can be classified into primary and secondary cases.

Primary peritonitis occurs spontaneously without any pre-existing pathological process in the abdomen. In cats, feline infectious peritonitis is the most common cause of primary peritonitis.

Secondary peritonitis occurs as the result of a pre-existing pathological process within the abdomen. It can be further classified into septic or non-septic peritonitis, where septic peritonitis results from direct bacterial infection of the peritoneal cavity. Septic peritonitis is the most common form in the dog and its causes include:

• Perforation of the gastro-intestinal tract due to foreign bodies, intussuscepta, invasive neoplasia, deep ulceration or dehiscence of surgical wounds or biopsy sites. Peritonitis as a result of wound dehiscence is most likely to occur 3-5 days post-operatively.
• Penetration of the abdomen by a stick, gunshot or other foreign body.
• Rupture of an infected uterus (pyometra), biliary tract or urinary tract.

The bacteria causing septic peritonitis or their products may spread systemically causing sepsis or endotoxaemia.

Non-septic peritonitis may occur due to the leakage of bile, urine or pancreatic enzymes (chemical peritonitis) or due to the presence of foreign substances such as barium or glove powder (physical peritonitis). In some cases of urinary tract or biliary tract rupture however, septic peritonitis may occur if the tracts were previously infected.

Diagnosis

Clinical Signs

The clinical signs are related to the presence of severe inflammation within the body cavity, with or without systemic infection.

• Abdominal pain, manifesting as a reluctance to move due to inflammation of the parietal peritoneum.
• Depression, anorexia and lethargy and non-specific signs of infection or systemic disease.
• Vomiting and diarrhoea may occur due to alterations in intestinal motility and functional ileus.
• Hypotension and (septic) shock due to effusion of fluid into the peritoneum and systemic vasodilation.
• Hypothermia or hyperthermia.

Laboratory Tests

Haematology

As with any severe inflammatory process, leucocytosis will occur. Initially, this is caused by neutrophilia which may have a left shift or, if very severe, a degenerative right shift. Severe localised inflammation may stimulate a leukaemoid response with massive mobilisation of neutrophils from the bone marrow pools.

Haemoconcentration (causing a raised packed cell volume (PCV) and total protein concentration) may occur due to loss of extracellular fluid.

Biochemistry

• Hypoproteinaemia.
• Hypoglycaemia - possible sepsis
• Increased lactate concentration
• Azotaemia
• Hypokalaemia
• Metabolic acidosis

Diagnostic Imaging

Radiography

• Abdominal radiography may reveal free gas in the abdomen. This is highly suggestive of peritonitis. The visceral details are loss. If radiograph is taken with the patient standing, a fluid line may be seen.
• Thoracic radiograph should be assessed for signs of metastatic disease.

Ultrasonography

• This is sensitive to detect free fluid in the abdomen.
• Possible causes such as abscesses of organs or rupture of gall bladder can be identified.
• It can be used to assist abdominocentesis.

Histopathology

• Abdominal fluid can be collected for laboratory analysis via abdominocentesis. The fluid should be stained for intracellular bacteria and assessed for:
  • amylase and lipase for pancreatitis
  • bile for biliary leak
  • creatinine for urine
  • glucose (<2.8 mmol/l) and lactate (>5.5 mmol/l) for sepsis

Treatment

It is vital to identify cases which require emergency surgical intervention. Any of the following is a major indication:

• positive for intracellular bacteria.
• free gas visible in the abdominal radiograph.
• presence of penetrating injuries in the abdomen.

Medical

Fluid therapy

• Aggressive fluid therapy with crystalloid and colloid should be given on initial presentation to improve haemodynamic parameters.
• Fluid therapy is also very important in the postoperative period. Both crystalloid and colloid should be continued until the patient is normotensive. However, if hypotension continues, a vasopressor such as vasopressin should be considered.
• Supplementaion of glucose and potassium may be needed.
• If severe metabolic acidosis is present, bicarbonate may be given.
• Septic peritonitis can cause disseminated intravascular coagulation (DIC) and therefore plasma can be given to replace clotting factors.

Antimicrobial

• Broad spectrum antibiotics should be given, preferably following culture and sensitivity test. Escherichia coli, Clostridium spp. and Enterococcus spp. are most commonly isolated.

Surgery

This may be indicated if the cause of peritonitis is undetermined or intestinal rupture or intestinal obstruction or mesenteric avulsion is suspected. Abdominal lavage is controversial due to the possibility of dissemination of infection. It is indicated in cases of generalised peritonitis but care has to be taken in cases of localised peritonitis. As much of the fluid used for lavage has to be drained as it will hinder the body’s immune system otherwise.

Prognosis

Guarded. Peritonitis is a multifactorial disease and the consequence is fatal in most cases. A rapid diagnosis and treatment may improve the prognosis.

• Fibrinohaemorrhagic peritonitis in infectious canine hepatitis
• Septic peritonitis caused by various agents, often Escherichia coli and anaerobic bacteria through perforation of the gut, rupture of urinary bladder or an abscess
• Putrid peritonitis in uterine rupture with pyometra or septic metritis
• Nocardia infection reults in profuse pink/red fluid due to blood and chronic inflammatory cells
• Granulomatous peritonitis caused by fungi, Nocardia and Actinomyces

Cats

• Putrid peritonitis in uterine rupture due to pyometra or fetal putrefaction
• Peritonitis due to penetrating wounds
• Septic peritonitis due to anaerobes in cat bite abscesses
• Serous peritonitis in cats with feline infectious peritonitis especially in the wet form but exudate occurs also in the dry form
  • Viscous, clear, pale to deep yellow fluid, may contain strands of fibrin

References

• Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier
• Nelson, R.W. and Couto, C.G. (2009) Small Animal Internal Medicine (Fourth Edition) Mosby Elsevier.
• Tilley, L. P. & Smith, F. W. K. (2007) Blackwell's Five-minute Veterinary Consult: Canine & Feline (Fourth Edition) Blackwell Publishing

For further information on peritonitis see: [1] In Pra