What Is Peritonitis?


Peritonitis is the inflammation of the peritoneum, an important membrane that makes up the lining of the abdominal cavity. The peritoneum is formed of two layers:

  • Parietal layer - this layer lines the inside of the abdominal and pelvic cavity 
  • Visceral layer - this layer envelops the internal organs, acting as a protective insulator

The peritoneal cavity is found between the two membrane layers. It typically contains a small amount of peritoneal fluid. This fluid acts as a lubricant, reducing the friction when organs rub against each other. 

The peritoneum carries blood, lymphatic fluid and nerves to the abdominal organs. This means that if the peritoneum is damaged, we feel pain. If the problem lies within the parietal layer, this pain is somatic. In other words, it is well-localised, allowing us to detect exactly where the pain is coming from, as this layer of the peritoneum receives the same nerve supply as the wall of your abdomen. However, if the problem is located within the visceral peritoneum, the pain is poorly localised, which is known as referred pain. This is because the visceral layer receives the same nerve supply as the internal organs, so it is harder to pinpoint the exact location of the pain. 

The peritoneum can also act as a barrier to infection due to its continuous layer protecting the abdominal cavity and its highly absorbent nature. It recognises harmful organisms and directs the immune system towards them. It also filters blood and fluid in the peritoneum to remove waste products. When these functions are impeded, the body becomes susceptible to infections and waste accumulation. As such, inflammation of the peritoneum is a serious medical condition, requiring urgent care.1 

In this article, we will explore all facets of peritonitis, including its causes, symptoms, and treatment. 

Causes of peritonitis

Peritonitis can be classed depending on whether the inflammation arises directly from the peritoneum (primary peritonitis) or if the source is elsewhere (secondary peritonitis). It can also be classified by identifying whether the source of inflammation is infectious (septic peritonitis) or not (aseptic peritonitis).

Primary peritonitis is often infectious, the most common form being spontaneous bacterial peritonitis. This form of peritonitis usually has no clear source of infection and is common in individuals with liver or kidney disease.2

Secondary peritonitis is caused by damage to an organ inside the abdominal cavity. Situations in which the damage can occur include: 

Secondary peritonitis can be septic if bacteria has spread from an infected organ or has been introduced due to an injury. Otherwise, aseptic peritonitis is caused by the peritoneum being exposed to sterile fluid, such as:

  • Bile from the gallbladder
  • Urine 
  • Pancreatic enzymes 
  • Foreign materials4

Rarely, peritonitis can occur as a complication of peritoneal dialysis, a procedure that helps remove waste products from the blood when the kidneys are not working properly. This procedure is performed by inserting a catheter (tube) through your abdomen, allowing a cleaning fluid to filter through, and discarding waste products. Peritoneal dialysis is an alternative to haemodialysis and can be performed at home. However, it does pose a risk of infection because a tube is inserted into the body.

Sometimes, after treatment, secondary peritonitis might not be resolved. Tertiary peritonitis is defined as an infection inside the abdominal cavity that continues or recurs 48 hours after treatment with surgery.5

Signs and symptoms of peritonitis

Common peritonitis symptoms include: 

  • Abdominal pain or tenderness 
  • Bloating (feeling of fullness) 
  • Abdominal distension 
  • Fever 
  • Loss of appetite 
  • Nausea and vomiting 
  • Diarrhoea or constipation
  • Reduced urine production
  • Feeling tired and confused 

Additionally, for those receiving peritoneal dialysis, there may be additional signs can indicate the presence of peritonitis if the peritoneal fluid is examined.

The peritoneal fluid can be observed for specific changes, such as:

  • Unusual colour 
  • White flecks 
  • Strands or clumps 
  • Unusual smell
  • Colour change or pain around the catheter site

Management and treatment for peritonitis

Septic peritonitis requires treatment with antibiotics, given through the vein (intravenously) in a hospital. Due to the severity of the condition, treatment can last up to two weeks to ensure that the infection has been cleared. 

In some cases, surgery is required to remove all the infected, dead tissue. This procedure is called debridement. It is used for the management of peritonitis as the removal of debris and dead tissue allows healthy tissue to grow back. Surgery is also important in cases of secondary peritonitis as surgical repair or removal of burst organs is needed to stop the source of infection and prevent death. 

Pain medication, replacement of fluids, oxygen, and even blood transfusions may be required to help fight peritonitis. 

If peritoneal dialysis is the cause of infection, an alternative form of dialysis, such as haemodialysis, should be used to allow your body to recover. 

In cases of spontaneous bacterial peritonitis, draining fluid that has accumulated in the abdominal cavity (ascitic fluid) can help manage the infection. Replacement of a protein called albumin is also necessary because otherwise, fluid within the body will continue to move into the abdominal cavity.2

Eating while you have peritonitis can be difficult. Sometimes, food can be delivered directly to the stomach, either by a tube going through your nose (nasogastric tube), or by a tube that is surgically inserted into the stomach (PEG tube). Alternatively, nutritional supplements can be administered directly into the bloodstream to help prevent nutrient and vitamin deficiencies.


How is peritonitis diagnosed?

Healthcare providers can suspect peritonitis based on symptoms and your medical history. To confirm their diagnosis, or rule out other problems, additional tests are required. These include:

  • Blood tests - blood samples are taken to detect signs of infection and inflammation. A blood culture may be performed to see if there are any bacteria present 
  • Imaging - X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI) scans or an ultrasound scan can be used to investigate the abdominal cavity and detect damage in your digestive system 
  • Peritoneal fluid analysis - a thin needle (or a catheter, if the patient is undergoing peritoneal dialysis) is used to sample peritoneal fluid to check for signs of infection, inflammation and bacteria.

How can I prevent peritonitis?

During peritoneal dialysis, antibiotics can be given prophylactically, meaning that they are used to prevent infections rather than treat them. However, this is not routine practice, as giving unnecessary antibiotics may lead to antibiotics working less effectively in the future.6

Ensuring good hygiene can help reduce the likelihood of peritonitis as contamination of the catheter used in peritoneal dialysis may be another cause of infection. Steps that can be taken include:

  • Washing your hands thoroughly before touching the catheter 
  • Cleaning the skin surrounding the catheter daily 
  • Wearing personal protective equipment during the peritoneal dialysis procedure 

Who is at risk of peritonitis?

Typically, adults with serious chronic liver disease, such as liver cirrhosis, are most at risk of developing spontaneous bacterial peritonitis. People with liver disease tend to have a poorly functioning immune system. Furthermore, due to increased pressure within the liver, fluid can accumulate in the abdominal cavity, which is referred to as ascites. This excess fluid acts as the perfect environment for bacteria, making infection all the more likely. Individuals who suffer from the following conditions are also at an increased risk of developing peritonitis:

  • Heart failure 
  • Lupus
  • Kidney failure 
  • Cancer 2

Malnutrition and the presence of harmful bacteria that are resistant to drugs can cause some people to develop tertiary peritonitis.5

When should I see a doctor?

Peritonitis is a serious condition that can quickly become life-threatening. The infection can spread from the peritoneum to the blood, resulting in sepsis (or blood poisoning). If you are concerned that you have peritonitis, contact your healthcare provider immediately. Symptoms to look out for include:

  • Sudden abdominal pain that is worse when moving or when touched 
  • Fever
  • Reduced urine production
  • Thirst 
  • Nausea and vomiting 
  • Constipation


Peritonitis is defined as inflammation of the peritoneum, which usually results from an abdominal infection or injury. It can become serious quickly, requiring urgent diagnosis and treatment to prevent life-threatening complications. Management involves administering antibiotics, performing surgery and ensuring that the patient is not malnourished. 

For those who are at an increased risk of developing peritonitis, including individuals with liver disease and those who perform peritoneal dialysis, it is important to be aware of possible symptoms and signs. It is imperative that you get in touch with your healthcare provider immediately if you suspect that you may have peritonitis. 

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