Peritonitis

The peritoneum is a thin, moist membrane that lines the abdomen from the inside and wraps around the bowel, the liver and the spleen. Spread out, it covers roughly the same area as the whole skin of the body, and it absorbs very quickly. So when bowel contents, bile, gastric juice or simply bacteria end up in the abdominal cavity, the inflammation does not stay in one corner: within hours the products of infection are in the bloodstream. Peritonitis is not a stomach upset to be slept off at home. It is a situation in which the outcome depends on how fast someone reaches a surgeon.

What happens inside the abdomen

Normally there are only a few spoonfuls of clear fluid between the two layers of the peritoneum, just enough for the loops of bowel to slide over one another. The cavity is sterile. When something foreign gets in, the peritoneum responds in the only way it can: it starts weeping fluid and fibrin, trying to glue the problem down and wall it off.

Sometimes that works and a walled-off collection of pus, an abscess, forms around the source. Far more often the inflammation spreads across the whole cavity. The irritated bowel stops contracting, gas and fluid stagnate inside it and the abdomen swells. Litres of fluid leave the circulation for the bowel wall and the cavity itself, so the person becomes dehydrated without losing anything outwardly. Blood pressure falls, the kidneys stop receiving blood, and bacteria and their toxins reach the bloodstream. That is sepsis, and it is sepsis rather than abdominal pain that determines how ill someone is.

What it feels like

The pain is usually sudden. When an ulcer perforates it arrives like a blow, and people remember the exact minute it began. With appendicitis or diverticulitis it is different: one spot hurts for hours or days, and then the pain spreads across the whole abdomen. That spreading is the moment the inflammation left the organ.

The most telling feature is that the pain gets worse with any movement. Coughing hurts, turning over in bed hurts, so does a car journey over a bumpy road. People lie still, on their back or on their side with their knees drawn up, and breathe shallowly. The abdominal muscles are tense and hard to the touch, and the belly stops moving with each breath.

Alongside this there is usually a high temperature with shivering, a fast pulse, nausea and vomiting, a dry mouth and thirst, bloating, no wind or bowel movements at all, and much less urine than usual.

The picture can be blurred. In older people, in people with diabetes, in anyone taking steroids or medicines that damp down the immune system, and in the days after an operation, the temperature may be normal and the abdomen soft. What stands out instead is weakness, confusion and a falling blood pressure. A missing textbook picture does not mean there is no peritonitis.

When to call an ambulance

Call an ambulance straight away if there is:

• severe abdominal pain that keeps building, stops you straightening up, and leaves the belly hard to the touch;
• abdominal pain together with a high temperature, shivering and a racing heartbeat;
• vomiting and a swollen abdomen with no wind and no bowel movements at all;
• confusion, cold clammy sweat, extreme weakness, or urine that has all but stopped;
• abdominal pain or fever in someone with cirrhosis or on peritoneal dialysis, even if it is mild and even if the abdomen is soft.

Across much of Europe the single emergency number is 112; elsewhere use your local emergency number. While you wait, do not eat or drink, since an anaesthetic is likely to be needed. Do not put heat on the abdomen. Do not take laxatives or use an enema, which are dangerous if something has perforated. It is also better not to take painkillers before you have been examined, and if you already have, say so.

Where peritonitis comes from

Most often it is secondary, meaning there is a definite source inside the abdomen:

• a perforated stomach or duodenal ulcer;
• appendicitis that has gone on to burst the appendix;
• diverticulitis that has broken through the bowel wall;
• a perforated bowel tumour;
• a strangulated hernia, and any loss of blood supply to the bowel that kills the wall;
• severe acute pancreatitis with infected necrosis;
• injury to the abdomen, whether penetrating or blunt;
• pelvic inflammatory disease and abscesses of the tubes and ovaries;
• complications of surgery and of endoscopic procedures: a leak where two ends of bowel were joined, or accidental damage to the wall.

Painkillers deserve a paragraph of their own. Long-term use of non-steroidal anti-inflammatory drugs and of aspirin is one of the main reasons ulcers form and eventually perforate, and such an ulcer often gives no warning pain beforehand. The risk is clearly higher in older people, in anyone who has had an ulcer before, and in anyone taking these drugs alongside steroids, anticoagulants or antiplatelet medicines. When the treatment has to continue for months, a doctor looks for the lowest dose that works and usually adds a medicine that protects the stomach lining. These drugs are not harmless to the kidneys either: they reduce renal blood flow, so in kidney disease they are used with real caution.

A separate case: cirrhosis and peritoneal dialysis

There is a form of peritonitis with no perforation at all, in which bacteria reach the cavity through the blood or across the bowel wall. It happens in cirrhosis of the liver once fluid has built up in the abdomen (ascites). It is called spontaneous bacterial peritonitis, and the danger lies exactly in how little it hurts: half of those affected have neither a rigid abdomen nor a high temperature. What raises suspicion is a sudden deterioration, confusion, deepening jaundice, worsening kidney function or an unexplained drop in blood pressure. The only way to confirm it is to draw off a little fluid with a needle and count the cells in it. Neither a blood test nor an ultrasound scan can make this diagnosis.

The second situation is peritoneal dialysis, where fluid is run into the abdominal cavity through a permanent catheter. This is about that technique, not about haemodialysis, where blood is cleaned through a machine and the peritoneum plays no part. Here the key sign is drained fluid that looks cloudy, sometimes with white flecks, and it may turn cloudy before any pain starts. Whenever it does, the bag is not thrown away: it goes to the dialysis unit, the fluid is sent for culture, and the antibiotic is usually given straight into the fluid being run in. If the infection does not settle or keeps coming back, the catheter has to be removed and haemodialysis used for a while.

What can look like it

Sudden abdominal pain is not yet peritonitis. Renal colic, gallstone colic, acute pancreatitis without perforation, a severe bout of gastroenteritis and an ulcer flare without perforation can all look similar. In women of childbearing age, ectopic pregnancy and ovarian torsion belong on the same list, which is why a pregnancy test is done regardless of how likely the patient thinks it is.

There is also the opposite trap: the abdomen hurts and the cause lies outside it. That is how an inferior heart attack, diabetic ketoacidosis, pneumonia at the base of the lungs in children, or shingles in its first days before the rash appears can present. Loss of blood flow in the bowel vessels deserves its own mention: the pain is savage, yet for the first hours the abdomen is soft and barely tender when pressed. That mismatch between what the patient describes and what the examination finds is itself a warning sign.

How the diagnosis is confirmed

It starts with an examination: the doctor checks how tense the wall is, whether it hurts when the hand is released suddenly, and listens to the abdomen, because in widespread peritonitis the bowel sounds fall silent. Blood tests follow — white cell count, C-reactive protein, lactate, creatinine, clotting — along with blood cultures taken before the first dose of antibiotic.

A plain abdominal X-ray taken standing up may show free gas under the diaphragm, direct proof that a hollow organ has perforated, though its absence rules nothing out. The main test is a CT scan with contrast: it usually shows both the peritonitis and its source, and the source decides what operation is needed. Ultrasound sees fluid well and is useful when a gynaecological cause is suspected, but with a distended bowel much of the abdomen stays hidden behind gas.

If there is ascites, a diagnostic tap is done. When someone is very ill and the picture still will not clarify, the diagnosis is made in theatre: a laparoscopy is performed and the cavity inspected from within. Normal blood results do not cancel an operation if the examination and the scans say otherwise.

How it is treated

Treatment always happens in hospital. In the first hours what matters is replacing the lost fluid through a vein, passing a tube into the stomach if there is vomiting and distension, and starting broad-spectrum intravenous antibiotics as early as possible. Once the culture comes back, the regimen is narrowed to the drug that works against the organism found. Pain is treated properly: the notion of enduring it so as not to mask the picture was abandoned long ago.

Then the source has to be dealt with, and without that antibiotics will not be enough. A perforated ulcer is stitched, a burst appendix removed, a damaged length of bowel resected, sometimes with a temporary stoma that is closed later. The cavity is washed out. A well walled-off abscess often needs no operation and is drained with a fine tube guided by ultrasound or CT.

The bowel does not recover at once, so for a few days feeding is arranged differently: through a tube passed into the small bowel, or into a vein if the bowel is not working at all. Spontaneous bacterial peritonitis in cirrhosis is not operated on. It is treated with antibiotics and intravenous albumin, after which long-term preventive antibiotics and assessment for a liver transplant are discussed, because one episode makes the next much more likely.

Online consultation

An acute abdomen cannot be sorted out online: if the pain is severe right now, what is needed is an ambulance, not a message. An online appointment is genuinely useful around this problem, though. After discharge, a doctor can go through the hospital summary, explain which parts of healing are normal and which mean going back, and say when physical effort and work can resume. With anyone on peritoneal dialysis it is worth revisiting bag exchange technique and the rule that cloudy fluid means contacting the unit the same day. With anyone who has cirrhosis and ascites, the subject is preventive treatment and how long it should run. And if you have been taking anti-inflammatory painkillers for years, the conversation about protecting your stomach and about what else could be used is better had before a perforation than after one.

This material is for information only and does not replace medical advice.