Peritonitis
Peritonitis is inflammation of the peritoneum, the membrane lining the abdominal cavity. In surgical practice it almost always means that something inside the abdomen has perforated, leaked or become gangrenous, releasing its contents into a sterile space. It is one of the conditions in which the time from onset to definitive treatment matters more than almost anything else, because the peritoneum has an enormous surface area and the systemic consequences are correspondingly rapid.
How it develops
The peritoneum has a surface area roughly comparable to that of the skin, and it is highly absorptive — a property exploited in peritoneal dialysis. That same property is what makes peritonitis dangerous: bacteria, toxins and inflammatory mediators released into the cavity are absorbed rapidly into the circulation.
The sequence:
- Contamination. Bacteria, gastric acid, bile, pancreatic enzymes, urine or faeces enter the peritoneal cavity.
- Chemical injury, then bacterial infection. Gastric acid and pancreatic enzymes cause immediate chemical peritonitis; bacterial infection follows within hours. Faecal contamination is bacterial from the outset and is the most severe.
- Inflammatory response. Mesothelial cells and resident macrophages release cytokines; neutrophils are recruited in large numbers; capillary permeability increases throughout the peritoneum.
- Massive third-space fluid loss. Litres of protein-rich fluid pour into the peritoneal cavity and the inflamed bowel wall. The patient becomes profoundly hypovolaemic while appearing merely unwell — this is the principal reason for early deterioration, and the reason resuscitation is as urgent as the operation.
- Paralytic ileus. The inflamed bowel stops propelling, distends with fluid and gas, and compounds the fluid loss.
- Systemic sepsis. Absorbed toxins and mediators produce vasodilatation, capillary leak, myocardial depression and multi-organ failure.
The body attempts containment. The omentum — aptly called the abdominal policeman — migrates toward inflamed areas and adheres, walling off the contamination; adjacent bowel loops and fibrin do the same. When containment succeeds, the result is a localised abscess rather than generalised peritonitis. When it fails, contamination spreads throughout the cavity.
The classification that determines treatment
- Primary (spontaneous) peritonitis — infection of the peritoneal cavity with no perforation or surgical source. It occurs in patients with ascites, most often from cirrhosis, where bacteria translocate across the bowel wall into fluid with impaired defences. It also occurs in patients on peritoneal dialysis and in children with nephrotic syndrome. It is treated with antibiotics, not surgery, and operating on it is harmful — which is why the distinction matters.
- Secondary peritonitis — the surgical form, resulting from perforation or gangrene of an abdominal organ. This accounts for the great majority.
- Tertiary peritonitis — persistent or recurrent peritonitis after apparently adequate treatment of secondary peritonitis, typically in critically ill patients, with resistant or opportunistic organisms. Difficult to treat and associated with high mortality.
Causes of secondary peritonitis
- perforated peptic ulcer
- perforated appendicitis
- perforated diverticulitis
- perforated colorectal or gastric cancer
- gangrenous or perforated gallbladder; bile leak
- bowel ischaemia or infarction
- strangulated hernia
- anastomotic leak after surgery
- trauma, penetrating or blunt
- perforation at endoscopy
- gynaecological causes — pelvic inflammatory disease, ruptured ectopic pregnancy, ovarian torsion
- tuberculous peritonitis, which is chronic and presents quite differently
Symptoms
- Severe abdominal pain, typically sudden in onset with perforation, constant rather than colicky, and worse on any movement — patients lie still, in contrast to the restlessness of colic
- pain on coughing, on the journey to hospital over bumps, and on deep breathing
- nausea and vomiting
- absolute constipation as ileus develops
- fever, tachycardia, rapid shallow breathing, hypotension
- On examination: a rigid, board-like abdomen, generalised guarding, rebound and percussion tenderness, and absent bowel sounds
- shoulder tip pain from diaphragmatic irritation
Signs may be muted — and the diagnosis correspondingly delayed — in the elderly, in patients on corticosteroids or immunosuppression, in those with diabetes or obesity, in patients receiving strong analgesia, and in those with spinal injury. In these groups the threshold for imaging should be low, and a patient who is simply "not right" after abdominal surgery deserves investigation rather than reassurance.
How the diagnosis is made
- Clinical assessment is paramount. A patient with generalised peritonitis and shock should go to theatre after resuscitation, without waiting for imaging.
- Blood tests — white count, C-reactive protein, lactate (an important marker of tissue hypoperfusion and ischaemia), renal function, amylase, liver tests, clotting and blood gases.
- Erect chest X-ray — free gas under the diaphragm confirms perforation, but is absent in a significant proportion.
- CT of the abdomen and pelvis with contrast — the investigation of choice where the patient is stable. It identifies free gas, free fluid, the site of perforation, abscesses and ischaemia, and frequently changes the operative plan.
- Ultrasound — useful at the bedside, particularly for free fluid, gallbladder disease and gynaecological causes, and in pregnancy.
- Diagnostic paracentesis — essential in a patient with ascites and suspected primary peritonitis. A neutrophil count above 250 cells/mm³ in the ascitic fluid establishes spontaneous bacterial peritonitis and directs treatment to antibiotics rather than surgery.
Treatment
Resuscitation
Immediate and aggressive, and it runs in parallel with diagnosis rather than after it: large-bore intravenous access, generous crystalloid, oxygen, catheterisation with hourly urine measurement, nasogastric decompression, analgesia, and broad-spectrum antibiotics within the first hour. The volume deficit is usually much larger than it appears, and under-resuscitation before anaesthesia is a recognised cause of catastrophic hypotension on induction.
Source control
This is the principle that governs everything. Antibiotics do not treat peritonitis; they support the treatment of it. The source of contamination must be dealt with:
- close the perforation, or resect the perforated segment
- remove the gangrenous organ
- drain the abscess
- wash out the peritoneal cavity thoroughly
The specific operation depends on the cause — omental patch repair of a perforated duodenal ulcer, appendicectomy, Hartmann's procedure or resection with anastomosis for perforated diverticulitis or cancer, cholecystectomy, resection of infarcted bowel.
Laparoscopy is used both diagnostically and therapeutically in stable patients and reduces wound complications. Percutaneous drainage by interventional radiology is the treatment of choice for a localised abscess and often avoids surgery altogether.
Damage control and the open abdomen
In the physiologically compromised patient — acidotic, hypothermic and coagulopathic — a prolonged definitive operation is often the wrong choice. An abbreviated procedure controls the source and stops contamination, the abdomen is temporarily closed with a negative-pressure dressing, the patient is stabilised in critical care, and definitive reconstruction is performed at a second operation a day or two later. Planned relaparotomy is used where contamination is severe and ongoing.
Abdominal compartment syndrome — raised intra-abdominal pressure from oedematous bowel and fluid, compromising ventilation, renal function and venous return — must be recognised and treated by decompression.
Antibiotics
Broad-spectrum cover against Gram-negative and anaerobic organisms initially, narrowed according to culture results. Duration is guided by source control: once the source is controlled, a short course of around four days is as effective as a longer one, a change from historical practice. Antifungal cover is considered in upper gastrointestinal perforation, in the immunosuppressed and in tertiary peritonitis.
Supportive care
Organ support in critical care, early nutrition (enteral wherever possible), thromboprophylaxis, glycaemic control, and physiotherapy.
Recovery
Recovery depends on the cause, the delay before treatment and the patient's physiological reserve. A promptly treated perforated ulcer in a fit patient may mean five days in hospital and a month's recovery. Established faecal peritonitis with septic shock in an elderly patient means weeks in hospital, often with a stoma, and a recovery measured in many months, with a meaningful mortality.
The difference between those two courses is largely the time from onset to treatment, which is the reason this condition is presented so urgently.
When to seek help urgently
Severe abdominal pain that is constant, worse on movement, and accompanied by feeling very unwell requires emergency assessment immediately. Do not wait to see whether it settles, do not take painkillers and go to bed, and do not eat or drink in case an operation is needed. If you have had recent abdominal surgery and feel unexpectedly unwell, with pain, fever or simply a sense that something is wrong, that also warrants urgent assessment rather than reassurance.
Common questions
What exactly is peritonitis?
Inflammation of the lining of the abdominal cavity, almost always because something inside has leaked, burst or lost its blood supply. Because that lining has a very large surface area and absorbs readily, bacteria and toxins enter the bloodstream quickly, which is why it makes people so unwell so fast.
Why do I feel so ill so quickly?
Two reasons. Litres of fluid leak out of the circulation into the inflamed abdomen, so you become severely dehydrated even though nothing has visibly been lost. And bacteria and inflammatory chemicals are absorbed into the blood, causing sepsis. This is why drips are started urgently and often before the cause has even been identified.
Can antibiotics alone treat it?
Only in one particular form — where infection develops in fluid already present in the abdomen, usually in people with liver disease, without anything having perforated. That is treated with antibiotics, and surgery would be harmful. In the far commoner surgical form, antibiotics support the treatment but cannot substitute for dealing with the leak itself.
Will I need an operation?
Usually, yes, to close or remove whatever has perforated and to wash out the abdomen. Sometimes a localised collection can be drained with a needle guided by a scan instead, avoiding surgery. Which applies depends on the cause and on how contained the problem is.
Will I need a stoma?
It depends on the cause and how unwell you are. Joining bowel together in a contaminated abdomen in a very unwell patient carries a high risk of the join leaking, so a temporary stoma is sometimes the safer choice. Many are reversible after a few months once you have recovered.
Why was my abdomen left open after surgery?
In some very unwell patients, a shorter operation to stop the contamination is safer than a long definitive one, with the abdomen covered by a special dressing while you are stabilised in intensive care, and closed at a second operation a day or two later. It sounds alarming but it is a deliberate strategy that improves survival in this situation.
How long will recovery take?
It varies enormously. A perforation treated early in a fit person may mean under a week in hospital and a month to get back to normal. Established infection with sepsis in an older person means weeks in hospital and many months of recovery. The time between the pain starting and treatment is the biggest single factor.
How soon should I go to hospital?
Straight away. Sudden severe abdominal pain that is constant and worse when you move is a reason to go to an emergency department now, not in the morning. Delay is what turns a manageable problem into a life-threatening one.
Related conditions
Other conditions of the peritoneal disease covered on this site:
- Peritoneal metastases
- Pseudomyxoma peritonei
- Peritoneal mesothelioma
- Primary peritoneal cancer
- Intra-abdominal abscess
- Adhesions and adhesive bowel obstruction
This page provides general information and does not replace an individual medical consultation. Peritonitis is a medical emergency requiring immediate hospital assessment.