Peritonitis

By | 2011-08-09

Contents

1. What are the primary functions of the peritoneum?

The peritoneum is the highly permeable lining of the abdominal wall and viscera forming an empty cavity. A small amount of free fluid that acts as a lubricant between the abdominal organs is constantly being formed. Water and other soluble products freely diffuse across the membrane. This property allows for such life-saving procedures as peritoneal dialysis.

2. What is the normal character and amount of peritoneal fluid?

Normal abdominal fluid is clear with a specific gravity of 1.016, less than 2 gm / dl of protein and typically 2000-2500 large mononuclear cells. There is usually less than 1 H-l / kg of body weight of peritoneal fluid.

3. List the types of abnormal fluid, along with the cellular and protein characteristic of each, found in the peritoneal space.

Fluids with different characteristics are classified as transudates, modified transudates, or exudates, according to the following criteria:

CELLS PROTEIN
< 2.5 gm / dl 2.5-7.5 gm / dl > 3.0 gm / dl
< 1500 / μl Transudate    
1000-7000 / μl   Modified transudate  
> 7000 / μl     Exudate

 

4. List the most likely differential diagnoses for transudates, modified transudates, and exudates.

 

Transudates Modified Transudates Exudates
Hepatic insufficiency Cardiovascular disease Septic peritonitis
Protein-losing enteropathy Feline infectious peritonitis Bile peritonitis
Protein-losing nephropathy Bile peritonitis Hemoabdomen
Uroperitoneum Hemoabdomen Chylous effusion
  Chylous effusion Uroperitoneum
  Uroperitoneum Neoplasia
  Neoplasia  

 

5. What is peritonitis?

The term peritonitis describes any inflammatory process involving the peritoneum and the peritoneal cavity. Feline infectious peritonitis is the only primary peritoneal disease. More often peritonitis is a sequelae of another disease process or an insult associated with disruption of the abdominal viscera or an external wound into the abdominal cavity. Secondary peritonitis usually has an acute or peracute onset with serious systemic symptons and signs.

6. What is the etiology of feline infectious peritonitis (FIP)?

Feline infectious peritonitis is a highly contagious, systemic, immune-mediated disease caused by a coronavirus. Chronic effusive peritonitis is the classic manifestation of the wet form of the disease, but the peritoneum is only one of many systems affected. Effusion and inflammation result from perivasculitis and subsequent increase in vascular permeability.

7. Outline the major causes associated with secondary peritonitis.

 

Bacterial Chemical Combined / Miscellaneous
Pyometritis Uroabdomen Neoplasia
Gastrointestinal compromise Pancreatitis (pancreatic enzymes) Iatrogenic foreign bodies (e.g., sponges, suture)
Surgical wound dehiscence Gastrointestinal fluid (rupture, perforation)
Pancreatic abscess Granulomatous (glove powder)
Prostatic abscess Bile (biliary tract disruption) Contrast media (barium, iodides)
Penetrating foreign body   Feline infectious peritonitis
Puncture or bite wound    

 

8. What are the main categories of peritonitis?

Peritonitis is characterized as either localized or diffuse (generalized). Presentation, diagnosis, treatment, and prognosis differ dramatically between the two forms. Localized peritonitis may or may not require medical intervention; however, if uncontained it may rapidly develop into a diffuse or generalized condition that is potentially life-threatening. Because of the nature of the peritoneum, generalized peritonitis may have profoundly damaging effects on other organ systems.

9. What are typical manifestations of generalized peritonitis?

Animals with generalized peritonitis commonly present with historical and physical abnormalities associated with the primary disease (see question 7). Patients are usually in hypovolemic shock and have marked abdominal pain, although the animal may present with vague, nonspecific signs early in the course of disease. The patient may present with obvious abdominal distention and a fluid wave (succussion) may be elicited on abdominal ballottement. Many animals with peritonitis have a recent history of abdominal surgery. Other historical information that may raise the suspicion of peritonitis may include foreign body ingestion, administration of nonsteroidal antiinflammatory drugs, or administration of immunosuppressive or chemotherapeutic drugs.

10. Is peritonitis always painful?

With acute or peracute onset of diffuse peritonitis, the animal exhibits signs of pain on abdominal palpation. Animals with severe abdominal pain often assume a praying position (the forelimbs are bent, and the rear quarters are elevated in the air with extended legs.) Peritonitis that develops over an extended period, such as feline infectious peritonitis, is usually not painful.

11. How does the peritoneum respond to injury?

The initial response is an increase in vascular permeability and subsequent influx of fluid. Increases in cell population and total protein are due to the presence of blood, albumin, fibrin, and debris. Fibrin is produced in an attempt to wall off the insult; it also allows adhesions to form between structures in the peritoneal cavity. Because of the large surface area of the peritoneum, fluid loss can be massive and ultimately results in decreased cardiac output, decreased perfusion, cellular hypoxia, and organ dysfunction. Diaphragmatic lymphatic clearance and macrophage phagocytosis are the first responses to contamination. Rapid neutrophil migration follows. Fibrin production is increased in an attempt to wall off the insult; it also allows adhesion to form between structures in the peritoneal cavity. The amount of protein in the fluid also is increased because of the presence of albumin, blood, fibrin, and necrotic cellular debris.

12. What is the simplest and most rewarding way to diagnose peritonitis?

Abdominocentesis for collection of fluid for cytologic evaluation is the least invasive and quickest way to diagnose peritonitis. If a fluid wave can be ballotted, a single midline pericentesis is usually successful. A four quadrant pericentesis is performed if there are small amounts of fluid, if compartmentalized disease is suspected, or if a midline pericentesis is negative. Usually the animal is standing or in lateral recumbency. The bladder is expressed to avoid unintentional cystocentesis. The abdomen is clipped, antiseptically prepared, and divided into four quadrants, cranial and caudal to the umbilicus and on either side of the ventral midline. A 20-gauge, 1-inch needle is inserted perpendicular to the midline into each of the four quadrants. Fluid should be allowed to drip out the open end of the needle and initially collected into a tube of ethylenediamine tetraacetic acid (EDTA) for cytologic analysis, which should include protein measurement and differential cell count. Other potential tests, as dictated by the suspected primary cause, include culture and sensitivity testing and measurement of packed cell volume, blood urea nitrogen (BUN), creatinine, total bilirubin, amylase, lipase, or triglycerides.

13. What if no fluid is retrieved from the abdominocentesis?

A negative abdominocentesis does not rule-out peritonitis. The technique descibed in question 12 commonly yields false-negative results, especially if only a small amount of fluid is present. Alternatives include use of a larger-gauge needle, an over-the-needle catheter, or placement of a peritoneal dialysis catheter. Diagnostic peritoneal lavage may be performed using an 18 or 20-gauge, 1 ‘A-inch over-the-needle catheter. After the area is prepared, the catheter is inserted into the abdomen and the stylet is removed. Warm isotonic fluid (22 ml / kg) is then infused into the abdomen through the catheter. After the fluid is allowed to disperse and mix in the abdomen momentarily, it is aspirated back and examined cytologically and biochemically.

14. After a routine, uncomplicated exploratory laparotomy, what type of fluid does postoperative abdominocentesis retrieve?

The fluid should be highly cellular representing a mild inflammatory reaction from the tissue manipulation. The primary cell population should be nondegenerate neutrophils. In a clean-contaminated surgery, such as an enterotomy, diaphagmatic lymphatics should clear mild bacterial contamination within 6 hours.

15. When is a peritonitis characterized as septic? What are the most common causes of a septic abdomen?

The presence of one bacterium in the abdominal fluid with high numbers of degenerate neutrophils characterizes the fluid as septic. The route of infection is usually from rupture of the gastrointestinal tract secondary to gastric dilatation-volvulus, mechanical obstruction, or breakdown of a previous surgical intestinal resection and anastomosis or enterotomy sites. Other possibilities include rupture of localized hepatic, pancreatic, or prostatic abscesses or contamination from pyometra.

16. What are the most common causes of a nonseptic exudate?

Nonseptic exudate usually is associated with inflammation from a chemical irritant such as urine, bile, pancreatic enzymes, or blood. The term nonseptic implies the absence of bacteria; however, nonseptic generalized peritonitis can quickly progress to septic peritonitis if not treated. Chemical, nonseptic peritonitis may cause adynamic ileus of the small intestine, resulting in compromise of the lumen and possible induction of septic peritonitis due to bacterial translocation.

17. What are the typical characteristics of an feline infectious peritonitis effusion?

The effusion associated with feline infectious peritonitis is usually a nonseptic, protein-rich, straw-colored fluid with a relatively low cell count. The fluid is viscous and foamy because of high protein content and often has visible strands or flecks of fibrin. The cell population is typically characterized as pyogranulomatous because of the predominance of macrophages and non-degenerative neutrophils. If the ratio of albumin to globulin in the effusion is > 0.81, feline infectious peritonitis is unlikely.

18. How can a suspected uroabdomen be confirmed?

Uroabdomen generally results in a transparent serosanguinous fluid and is initially aseptic unless an underlying urinary tract infection was already established. blood urea nitrogen and creatinine should be measured on the abdominal fluid and serum. The blood urea nitrogen should be roughly the same in both fluids as it rapidly equilibrates over the compromised membrane, whereas the concentration of creatinine is greater in abdominal fluid than in serum. Of interest, blood urea nitrogen is now found to be as accurate as creatinine in identifying acute uroabdomen.

19. Can pancreatitis-associated peritonitis be diagnosed using peritoneal effusions?

Peritoneal effusions associated with pancreatitis are generally classified as nonseptic, suppurative modified transudates or exudates. Comparison of serum and effusion amylase and lipase activities generally reveals higher activities in the effusion.

20. How do you differentiate between hemorrhagic effusion and blood pericentesis from a vessel or organ?

The packed cell volume of the fluid should be compared with that from the peripheral blood; if the values are different, a hemorrhagic effusion should be suspected. The absence of platelets and the presence of erythrophagocytosis on cytological examination of the fluid is also consistent with hemorrhagic effusion. If a moderate to large amount of fluid is collected, a sample should be evaluated for clotting; if clotting occurs, the fluid is either peripheral blood or peracute abdominal hemorrhage. Traumatic rupture of abdominal organs or vessels, coagulopathies, and neoplasia are common causes of hemoperitoneum.

21. Describe the lethal factors in peritonitis.

The prognosis for a patient with generalized peritonitis depends on the underlying primary cause or preexisting or concurrent disease, duration of the condition, and the patient’s physical status. However, certain concurrent conditions increase the likelihood of mortality. If hypovolemic shock develops or a mixed bacterial population or free hemoglobin is found in the effusion, alone or in combination, the prognosis is dramatically worsened. Hemoglobin is believed to enhance the virulence of bacteria by a mechanism not well understood.

22. Do abdominal radiographs have any diagnostic value in patients with confirmed peritonitis?

Fluid in the abdomen causes a ground-glass appearance on radiographs, which obscures serosal detail of abdominal organs. However, abdominal radiographs may delineate free gas in the abdomen, suggestive of gastric or intestinal perforation. This scenario is best appreciated on a standing lateral radiograph, which demarcates a line between fluid and free gas. Plain abdominal radiographs also demonstrate the presence of functional intestinal ileus which is a common complication of generalized peritonitis. The presence of the urinary bladder or abdominal masses may also be determined from survey films, if fluid volumes are minimal. Thoracic radiographs should be performed if the animal is showing any respiratory symptoms. Conditions identified on radiographs that may affect treatment options and prognosis include pleura] effusion, pulmonary edema, aspiration pneumonia, and metastatic neoplasia.

23. What other diagnostic tests may help to determine the cause of peritonitis?

Abdominal ultrasound is useful in finding an underlying cause of peritonitis such as pancreatitis. It also may detect pockets of small amounts of fluid, as in a localized peritonitis that can be associated with pancreas or liver abscess. A positive contrast cystourethrogram may help differentiate between a ruptured bladder or an avulsed ureter. An upper gastrointestinal series is indicated in some cases to confirm a mechanical obstruction or perforation of the bowel. However, often advanced imaging studies are not required and may delay therapy.

24. What are the significant metabolic alterations and sequelae associated with a generalized peritonitis? How could they be corrected or avoided?

Shock, metabolic acidosis, acute renal failure, acute hepatic failure, hypoglycemia, pancreatitis, sepsis, cardiac dysrrhythmias, pleural effusion, and disseminated intravascular coagulation are the most common secondary problems in animals with generalized peritonitis.

25. What is a suitable antibiotic choice for a septic abdomen?

Because the bowel is the usual source of bacteria in animals with septic peritonitis, single or combination antibiotics for empirical treatment of gram-negative, gram-positive, and anaerobic bacteria are indicated. In combination therapy, enrofloxacin or aminoglycosides are usually chosen for gram-negative organisms and combined with penicillins, first-generation cephalosporins, or clindamycin, each of which has a broad spectrum of action against gram-positive anaerobic organisms. If a single antibiotic is preferred, second-generation cephalosporins, third-generation cephalosporins, and imipenem are good choices. Initial empirical antimicrobial therapy should be started as soon as peritonitis is suspected and a sample of abdominal fluid is retrieved for culture and sensitivity testing.

26. At what point is surgery indicated? What are the primary goals of surgical intervention?

Every patient with septic peritonitis should be surgically explored to locate and correct the underlying cause and source of contamination. Surgery also allows for removal of foreign material, lavage of the peritoneal cavity, and, potentially, placement of peritoneal drains, gastrotomy feeding tubes, or jejunostomy feeding tubes. Irrigation of the abdominal cavity with large volumes of warm isotonic fluid aids removal of necrotic debris, potentially reduces adhesion formation, and dilutes the bacterial population, thus lessening the potential for abscess formation.

27. What subjective parameters may be used to determine organ viability?

Abdominal structures should be evaluated for blood supply based on color, thickness, temperature, and perfusion (arterial pulse; bleeding of incised surface). Peristalsis is also a good indicator of viability of the stomach and intestines.

28. What is the role of peritoneal drain systems in the treatment of peritonitis?

Peritoneal drains are useful for providing local drainage of intraabdominal abscesses or other pockets of localized peritonitis. Placement of a closed peritoneal drain for management of generalized peritonitis has been associated with many complications. Because of the peritoneum’s ability to respond rapidly to injury, most drainage systems are sealed over within 6 hours by fibrin and adhesion formation. Efficacy of peritoneal drains for continual effusion of abdominal fluid may be enhanced by placement of multiple drains and by intermittent or continuous peritoneal lavage. Cytologic evaluation of the effluent measures the patient’s progress and determines when the drains may be removed. The most effective type of abdominal drain is the sump-Penrose system, whereby a sump drain is placed inside a fenestrated Penrose drain. This configuration is thought to protect the abdominal viscera and to provide more efficient drainage than the use of Penrose, tube, or sump drains alone.

29. Describe complications associated with closed abdomen peritoneal drainage and peritoneal lavage.

Any type of drainage system provides a route for ascending infection. The introduction of foreign material into the peritoneal cavity causes an increase in inflammatory response and formation of adhesions. Drains may be directly damaging to abdominal viscera by erosion of the serosal surface. Problems with peritoneal lavage are associated with the introduction and removal of large amounts of fluid and loss of cells, protein, and electrolytes. The most likely complications are anemia, hypoproteinemia, hypokalemia, hyponatremia, and hypocalcemia. Hypothermia is easily avoided by the use of warm lavage fluids. Sterile occlusive dressings around the drain sites may minimize the risk of ascending infection.

30. How much of a benefit is there to leaving the abdomen open to drain? What are the advantages, disadvantages, and complications of open abdominal drainage?

Open abdominal drainage is believed to provide a more rapid and more effective means of drainage of the peritoneal cavity. The obvious risks are infection and sepsis as well as dehiscence and evisceration, but this can be avoided by frequent sterile bandage changes and close observation of the patient. At surgery, the abdomen is incompletely closed by loose apposition of the external rectus sheath in a simple continuous pattern. Subcutaneous tissue and skin may be left open or closed depending on the amount of local contamination. Sterile dressings are placed over the incision and secured to the patient with a circumferential abdominal wrap. This bandage should be changed as often as necessary, typically once or twice a day, and the quantity and appearance of the fluid should be evaluated. A major disadvantage is that this technique requires at least a second surgical procedure for completing abdominal closure. However, it also allows a second look to assess organ viability and surgical repairs and provides an opportunity for additional intraoperative lavage. Other complications include significant fluid and protein loss, resulting in hypovolemia, anemia, and hypoproteinemia. These conditions need to be recognized and treated appropriately.

CONTROVERSY

31. Should antibiotics or antispetics be administered intraabdominaiiy with generalized septic peritonitis?

Intraabdominal administration of antibiotics frequently is used in equine abdominal surgery and is advocated by some for use in small animals as well. However, antibiotics can increase the inflammatory reaction in the abdomen, increase the risk of adhesions, and may increase the risk of drug toxicity if the animal is receiving systemic antibiotics concurrently. Addition of antiseptics to the lavage fluid is also controversial due to risk of irritation and toxicity.

32. What role do corticosteroids and nonsteroidal antiinflammatory drugs (NSAIDs) have in treatment of generalized peritonitis?

The use of corticosteroids in septic animals remains controversial. Benefits of steroids include stabilization of vascular and lysosomal membranes, reduced adhesion formation, positive cardiac inotropic effect, and increased regional blood flow. Disadvantages to steroid use include gastrointestinal ulceration and potential immunosuppression in the face of potential infection. NSAIDs block prostacyclin and thromboxane A2 production, which may contribute to multiple organ failure. These drugs may also be helpful in treating acute endotoxic or septic shock. Flunixin meglamine (Banamine) has been shown to be beneficial in experimental models of septic peritonitis. However, the risk of adverse effects of NSAIDs, such as gastrointestinal ulceration and renal toxicity, makes their use in animals with septic peritonitis controversial.