What is the Peritoneum?

To understand peritonitis, it is firstly crucial to discuss the peritoneum and the structure the condition affects. The peritoneum is a serous membrane that lines the inside of the abdomen and covers most of the abdominal organs, which are known as the visceral organs.¹ The body contains three serous membranes: the pleura, pericardium and peritoneum, of which the peritoneum is the largest.² The peritoneum’s membrane is composed of two distinct layers: the parietal peritoneum, which covers the abdominal walls, and the visceral peritoneum, which covers the visceral organs.³

What are the functions of the Peritoneum?

The peritoneum has several functions but its most predominant one is the regulation of intraperitoneal homeostasis in the abdominal cavity.⁴ The abdominal cavity refers to the space within the parietal peritoneum, and within this cavity, there is also the peritoneal cavity, which is the parietal peritoneum and the visceral peritoneum; and the retroperitoneum, which is located behind the peritoneal cavity.⁵ The peritoneal fluid provides the environment for free movement of the abdominal organs, which is vital in processes such as digestion, and it also allows for the exchange of molecules which contribute to homeostasis within this space.⁶

Other functions of the peritoneum include the propagation of inflammation, antigen presentation and tissue repair.⁴ The inflammatory response and antigen presentation of the peritoneum are important steps in tissue repair when damage may occur for infection or injury.⁷

What is Peritonitis?

As mentioned before, inflammation is part of the function of the peritoneum in the process of tissue repair, however, sustained inflammation of the structure is known as the condition of peritonitis.⁸ This inflammation can be brought about by several causes, and this leads to differing classifications of the condition. 

Primary Peritonitis

Primary peritonitis is defined as an infection of the peritoneal cavity, which is not directly related to an intra-abdominal abnormality, such as an abscess or mass.⁹ The condition is also known as spontaneous bacterial peritonitis (SBP), as it predominantly occurs in the ascitic fluid, which occurs usually as a result of an underlying health condition such as cirrhosis of the liver.¹⁰ Hepatic cirrhosis or cirrhosis of the liver is caused by chronic damage or injury to the organ and is characterised by fibrosis (scarring) and nodule formation.¹¹ The incidence of primary peritonitis is rare in children but is estimated to occur in 25% of adults with alcoholic cirrhosis (cirrhosis caused by chronic alcohol consumption).⁹

Secondary Peritonitis

Whereas primary peritonitis is a result of an infection not directly caused by an intra-abdominal abnormality, secondary peritonitis describes the condition when the infection is directly caused by a spillage from either the gastrointestinal or urogenital tracts, which results in contamination of the peritoneum.¹² This type of peritonitis is more commonly observed as there are many potential causes for the abdominal perforation including: anastomotic leak, which occurs following surgery when sections of visceral organs have not been properly resealed, ischemic necrosis, which describes tissue damage due to a loss of blood flow, and direct injury to the abdominal organs.¹³

In primary peritonitis, the infection is more often than not monomicrobial, meaning only a single type of bacteria is present and causing harm, whereas in those with secondary peritonitis, due to the perforation within the peritoneal cavity, a whole host of bacteria can leak in, which often means the infection is polymicrobial.¹² 

Tertiary Peritonitis

Following on from secondary peritonitis, there is also a third condition which can describe a later stage of peritonitis. This is known as tertiary peritonitis and it requires two conditions for its diagnosis: an intra-abdominal infection that persists or recurs for over 48 hours, following a successful and adequate surgical intervention.¹³ As such, given the period and post-intervention nature of the diagnosis of tertiary peritonitis, it essentially exists on a continuum between conditions, whether that be primary or secondary peritonitis; although it more commonly originates from a diagnosis of the latter.¹⁴

How can Peritonitis be treated?

Surgery

As mentioned in the diagnosis criteria for tertiary peritonitis, the condition can only be reached following a surgical intervention to treat the initial primary or secondary peritonitis. Thus, a surgical route is often undertaken to treat peritonitis, particularly in secondary peritonitis cases.¹² The core principles of surgical management of secondary peritonitis are: eliminate the septic focus, remove necrotic tissue and drain purulent material.¹⁵ The removal of the septic focus (or more commonly, the source of infection) can be achieved through fairly routine procedures such as appendectomy (removal of the appendix) or omentopexy (suturing of the greater omentum to a nearby organ), however, in more serious cases, more invasive procedures such as gastrectomy (removal of part of the stomach) or colectomy (removal of part of the colon) may be required.¹⁶ 

Following the elimination of the septic focus and the removal of necrotic tissue, the next step in the surgical procedure is the draining of purulent material, which should be performed by aspirating the infectious fluid and then removing it by swabbing.¹⁶ A further step can be taken in managing secondary peritonitis and this can be either open management, performed via a planned laparostomy, which is a surgical procedure that opens and then leaves open the abdominal cavity; or it can be managed via planned relaparotomy.¹⁷ Planned relaparotomy refers to a planned surgical procedure that is undertaken in the same abdominal area as a prior procedure, within 60 days of the original.¹⁸ The advantage of opting for this route of surgical management is that it can more quickly spot signs of persisting or recurrent infection, before symptoms manifest themselves, at which point, the prognosis significantly worsens.¹⁶

Antibiotic therapy

Antibiotic therapy is an intervention that can be opted for alongside surgical management but also independently of it, however the course, strength and type of antibiotic treatment can greatly vary and should be tailored based on the cause of peritonitis and the symptoms presented.¹²

Psychological help

For patients with tertiary peritonitis, who have already undergone a surgical intervention, and have again suffered a recurrent infection, there are limited treatment options at hand for clinicians. This is also because they most likely will have already undertaken antibiotic therapy, and if the infection has persisted, the bacteria present will likely be antibiotic-resistant.¹⁹ As such, given the poor prognosis for the patient, it is likely they will benefit from psychological help to better meet their physical and emotional needs and guide them through the management of their condition.²⁰

Summary

The peritoneum is a serous membrane which lines the inside of the abdomen on its parietal side and covers most of the intra-abdominal organs on its visceral side, The space within the structure is known as the abdominal cavity, the space between the two layers of the peritoneum is known as the peritoneal cavity, and the space behind the peritoneal cavity is known as the retroperitoneum.

The peritoneum has many functions such as allowing the free movement of visceral organs, regulating the intra-abdominal homeostasis and initiating tissue repair through inflammation propagation and antigen presentation. However, these functions can be impaired when an infection results in inflammation of the peritoneum which can be classified based on three subtypes.

Primary peritonitis is defined as an infection in the peritoneal cavity that is not a result of any other intra-abdominal abnormality. This condition is heavily associated with liver cirrhosis and is oftentimes monomicrobial in origin. Secondary peritonitis however is an infection caused by spillage from a perforation in either the gastrointestinal or urogenital tract, and this leak of bacteria can be polymicrobial, and is often more severe. Finally, there also exists tertiary peritonitis, which can only be diagnosed following successful surgical intervention to treat a known abdominal infection, and a period of 48 hours following the intervention.

Secondary peritonitis is often treated surgically as there is a structural issue that needs addressing through procedures such as appendectomy, omentopexy, gastrectomy and colectomy. Following this open management or planned relaparotomy can be opted for to ensure infection does not persist. 

In the management of both primary and secondary peritonitis, antibiotic therapy can be used to fight the source of infection, however in tertiary peritonitis patients, the bacteria have often evolved to become resistant to treatment, and therefore, these patients may require more complex holistic and palliative care to support them during their illness.