The peritoneum is the membrane that covers all the organs of the abdomen (see Diagram –Gastrointestinal System). If bacteria spill out of the bowel into the abdomen, a horrible infection spreads all over the peritoneal cavity (under the membrane, over & around all the organs). One example is from a ruptured appendix. Without antibiotics & surgery, peritonitis is always fatal.
Abdominal pain may begin gradually or abruptly. Then comes nausea & vomiting, sooner or later a fever. Without treatment, the blood pressure drops, leading to death.
We suspect peritonitis if the abdomen is tender with even gentle palpating. Often it’s is rock hard. Often the patient can’t stand up straight, & walks doubled-over. Any jarring of the abdomen is very tender (if a child can jump off the exam table without pain, there’s no peritonitis).
We don’t do any tests to diagnose peritonitis. If we suspect it, we send the patient to an ER. If we’re working in an ER, we call a surgeon. There’s a more subtle type of peritonitis that occurs in persons with Cirrhosis of the liver. The scarred liver can cause ascites, fluid in the abdomen, which can get infected. Symptoms here may be minimal, maybe just new abdominal pain, or a fever. Such patients need an ultrasound or CT scan to see if there’s ascites; if so, it needs to be drained & examined for infection. This is done in an ER.