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 may occur due to loss of plasma proteins into the inflammatory exudate.

Hypoglycaemia may occur in cases of septic peritonitis.

Dehydration (which is also responsible for the haemococentration) may also result in pre-renal azotaemia, increased tissue lactate production and metabolic acidosis.

Hypokalaemia may occur as a result of chronic vomiting and it may contribute to the intestinal ileus which often develops in cases of peritonitis.

Diagnostic Imaging

Radiography

Plain radiographs of the abdomen may reveal the presence of free gas in the abdomen (pneumoperitoneum) due to intestinal perforation or bacterial production. The normal serosal detail may be effaced due to the presence of an abdominal effusion and, if a horizontal beam decubitus radiograph is made, a fluid line may be apparent.

In cases where neoplasia is thought to be the cause of the inflammatory process, thoracic radiograph should be assessed for signs of metastatic disease.

Ultrasonography

This modality has a high sensitivity for the detection of free fluid in the abdomen and it may be used to identify some specific causes of peritonitis, including abscesses of organs or rupture of the [[Biliary Tract - Rupture|biliary tract.

Ultrasound scans can also be used to guide abdominocentesis.

Other Tests

Free abdominal fluid can be collected under ultrasound guidance and submitted for cytological analysis. If fluid cannot be obtained on aspiration, diagnostic peritoneal lavage can be performed by istilling a small volume (~20 ml/kg) of warmed isotonic crystalloid into the abdomen, agitating the abdomen and then re-aspirating this fluid. Grossly, the fluid may contain vegetable fibres if the gastro-intestinal tract has ruptured or it may be evidently green (indicating the presence of bile) or haemorrhagic. On cytological examaintion, the sample should be assessed for the presence of neutrophils (and other leucocytes) with intracellular bacteria.

Further possible tests include:

Measurement of amylase and lipase where the cause is suspected to be pancreatitis
Bile where biliary tract rupture is suspected.
Creatinine and potassium if the effusion is thought to be a uroabdomen.
Glucose (<2.8 mmol/l) and lactate (>5.5 mmol/l) should be measured and, where their values are below those shown, the inflammation is likely to be septic.

In cats with Feline Infectious Peritonitis, the effusion usually has a high protein content (>35g/l) with a high globulin: albumin ratio. There is a variably high cellularity mainly composed of lymphocytes.

Treatment

It is vital to identify severe cases promptly as these will require emergency surgical intervention. Any of the following criteria is a major indication for surgery:

Presence of intracellular bacteria in leucocytes in the abdominal exudate
Pneumoperitoneum
Presence of penetrating injuries to 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: maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=haemoabdomen&searchid=1&FIRSTINDEX=0&sortspec=relevance&resourcetype=HWCIT In Practice article