Peritonitis and intra-abdominal abscesses
Peritonitis is inflammation of the peritoneum, which lines the peritoneal cavity. Initially, peritonitis is localised and contained by a wrapping of greater omentum, adjacent bowel and fibrinous adhesions.With ongoing inflammation, localised peritonitis may progress to a generalised peritonitis, associated with massive exudation of fluid, with resultant hypovolaemia, toxaemia and septicaemia if sepsis is present. Paralytic ileus is invariably present with generalised peritonitis.
The principal signs of peritonitis include tenderness, guarding, rigidity and rebound tenderness. With generalised peritonitis, the patient is very unwell, with marked fever, tachycardia and dehydration. There is diffuse abdominal pain, exacerbated by even the slightest movement.
Causes of peritonitis
Acute primary peritonitis
Acute primary peritonitis is rare and usually occurs in association with immunosuppression, such as postsplenectomy, nephrotic syndrome or in cirrhosis, where the proteinaceous ascitic fluid provides a good culture medium for bacteria. Sometimes it affects young girls following pelvic inflammatory disease. Common organisms are haemolytic streptococci, Escherichia coli and Klebsiella species. Acute primary peritonitis is often a diagnosis of exclusion and requires aggressive antibiotic therapy. (Common varieties of peritonitis)
Secondary peritonitis may be suppurative, chemical or chronic sclerosing.
Acute suppurative peritonitis may occur secondary to a disease process of an intra-abdominal organ; that is, perforation (e.g. peptic ulcer, diverticular disease, Crohn's disease, appendix or gall bladder), infection (e.g. appendix abscess, pyosalpinx) or ischaemia (volvulus, mesenteric ischaemia or strangulated hernia). Most of these cases will require urgent surgical intervention. Erect chest X-ray may show free gas beneath the diaphragm, indicating a perforated viscus (Erect chest X-ray showing free gas beneath the right hemidiaphragm.).
Chemical peritonitis may occur secondary to bile (displaced T-tube from common bile duct, unrecognised division of accessory bile duct) or blood (post-operative bleeding, abdominal trauma). Less commonly urine (ureteric injury in pelvic surgery or intraperitoneal rupture of bladder) may also be the cause. Bacterial contamination and overgrowth may develop.
Intra-abdominal abscesses are one extreme in the spectrum of bacterial peritonitis. They require drainage in addition to antibiotic therapy. The pathogenesis requires a polymicrobial infection, with the presence of foreign matter facilitating the development of progressive infection. The bacterial flora of the gastrointestinal tract varies from small numbers of aerobic streptococci and facultative Gram-negative bacilli in the stomach and proximal small bowel, to larger numbers of these species with an increasing number of anaerobic Gramnegative bacilli (Bacteroides spp.) and anaerobic Grampositive flora (streptococci and clostridia) in the distal ileum and colon. In patients who have received prolonged antibiotic therapy and in those with extended hospital stay, colonisation by yeasts such as Candida species or a variety of nosocomial pathogens may occur. Skin flora may be responsible following penetrating abdominal injuries. Pelvic abscesses in women may occur as part of pelvic inflammatory disease. Common organisms include Neisseria gonorrhoeae and Chlamydia trachomatis.
There are four functional compartments within the peritoneal cavity: pelvis, right and left paracolic gutters and the subdiaphragmatic spaces. In the recumbent patient, diffuse intraperitoneal fluid collects under the diaphragm and in the pelvis. These are the common sites for abscess formation. More localised abscesses may develop in relation to the affected viscus (e.g. abscesses in the lesser sac secondary to severe pancreatitis or a perforated peptic ulcer, or a peri-appendiceal abscess).
The clinical presentation of an intra-abdominal abscess is highly variable. In a patient with a predisposing primary intra-abdominal disease or following abdominal surgery, persistent abdominal pain, focal tenderness, swinging fever, persistent paralytic ileus and leucocytosis suggest an intra-abdominal purulent collection. The patient may simply fail to thrive and may have mildly abnormal liver function.
With a pelvic abscess, there may be urinary frequency, dysuria, diarrhoea or tenesmus due to irritation of the anatomically related organs. With a subphrenic collection, there may be shoulder tip pain, hiccups and unexplained pulmonary symptoms (pleural effusion, basal atelectasis).
Investigations in patients with suspected intraabdominal abscess include full blood examination, urea and electrolytes and liver function test. Blood cultures and other appropriate cultures (urine, sputum, catheter) may also be performed.
Computed tomography (CT) scan with iodinated soluble oral contrast is useful. Serial images are obtained from the diaphragm to the pelvis. It is particularly useful for localising small or deep intra-abdominal abscesses (Computed tomography scan showing a pelvic abscess.). Interpretation in post-operative patients can be particularly difficult, as loculated, noninfected serous collections are common physiological events.
Ultrasound equipment is mobile and examinations may be readily performed in a critically ill patient in the intensive care unit. However, the quality of such studies is not as good as a CT scan and is vastly operatordependent. Endovaginal ultrasound is particularly useful to detect tubo-ovarian abscess complicating pelvic inflammatory disease in women.
Laparoscopy is occasionally used if there is diagnostic uncertainty between a tubo-ovarian abscess and a phlegmon.
Parenteral antibiotics should be administered prior to drainage of the abscess. Initial choice of antibiotics is empirical but should provide a broad-spectrum activity against Gram-negative bacilli and anaerobes. Specific therapy is guided by the results of cultures. With adequate drainage of the abscess, it may not be necessary to treat each component of the polymicrobial flora. Commonly used antibiotics include metronidazole with a second- or third-generation cephalosporin or imipenem alone. Alternatively, combinations of amoxycillin, gentamicin and metronidazole provide additional cover against enterococci as well. In immunosuppressed patients, Candida species may have an important pathogenic role, and treatment with amphotericin B is indicated.
Computed tomography scan or ultrasound localises the abscess cavity and guides safe access for percutaneous drainage (Computed tomography (CT) scan of the abdomen showing a large subphrenic abscess that was aspirated percutaneously under CT guidance.), avoiding adjacent viscera and blood vessels. A diagnostic needle aspiration is initially performed to confirm the presence of the abscess and to obtain pus for Gram stain and culture. A largebore drainage catheter is then placed in the most dependent position. While percutaneous drainage is effective in a single, unilocular abscess, it is more limited in a multiloculated abscess, especially if the contents are tenacious.
Preliminary percutaneous drainage is useful in improving and reducing the sepsis, prior to definitive surgical treatment. In some cases, as for complicated diverticular disease or Crohn's disease, it may facilitate subsequent single-stage resection and primary anastomosis, rather than traditional multi-stage procedures with diversion. Repeat imaging with sinography or CT scan will estimate the size of the residual cavity and any enteric communication.
Surgical drainage is mainly undertaken in patients who have not improved with percutaneous drainage or in whom the collections are not appropriate for percutaneous drainage, as in multiple abscesses, severe necrotising pancreatitis or interloop abscesses with Crohn's disease. An extraperitoneal approach, if possible, is generally preferred because it limits the risk of further contamination of the peritoneal cavity. With a distally located pelvic abscess that is bulging, the drainage may be performed through the rectum or vagina. The loculae are gently broken down digitally and soft drains are placed in the most dependent position.