The presence of free gas within the peritoneal cavity is referred to as pneumoperitoneum. This condition is most commonly encountered in patients who suffered a perforation of the gastrointestinal tract and thus indicates the necessity of urgent intervention to prevent peritonitis, septic shock, and death.
PP patients may have a medical history of gastrointestinal disease or recent surgery, and corresponding anamnestic data should be considered when interpreting clinical signs, before deciding on a therapeutic approach. While the presence of free air in the peritoneal cavity cannot be diagnosed during a general examination, abdominal distension, intense pain, rigidity and rebound tenderness are indicative of peritonitis and possibly GIT perforation. In these cases, bowel sounds are usually absent and patients present constitutive symptoms like fever, volume depletion, hypotension and tachycardia; they may suffer from nausea and vomiting. Furthermore, patients may report not to have passed stools or gasses since symptom onset .
In contrast, postoperative PP doesn't generally cause major complaints, and mild to moderate abdominal distension and pain may merely result from the underlying disease or surgery. This condition should normalize within a week.
Abdominal imaging is the mainstay of PP diagnosis. To this effect, plain radiography has long since been the technique of first choice. Very small volumes of free gas - as little as 1 ml - can be observed in images obtained by means of this technique. Upright, anterior-posterior chest radiographs are most suited and typically depict a translucent, crescent area below the diaphragm . The Rigler's sign may be observed; it corresponds to the display of both sides of the intestinal wall . Similarly, the telltale triangle sign implies PP: A triangle of gas may be visualized between three adjoining bowel loops, or two loops and the peritoneal wall . In emergency settings, radiographs may be obtained from a patient in the supine decubitus position.
Computed tomography scans may be reserved for doubtful cases. Its superior spatial resolution is helpful to localize minimum quantities of free gas and to distinguish PP from pseudo- pneumoperitoneum. The latter term refers to any condition that mimics PP, such as pneumatosis cystoides intestinalis and interposition of viscera .
The term pneumoperitoneum (PP) refers to the presence of gas within the peritoneal cavity. Most commonly, this gas originates from the gastrointestinal tract (GIT) and thus indicates a disruption of its physical integrity. Any part of the GIT may be affected and PP may complicate diseases like gastric ulcer, mesenteric infarction, toxic megacolon, and abdominal cancer. Interestingly, perforated appendicitis seldom entails PP . Rarely, emphysematous inflammation of abdominal organs may give rise to PP . PP may also occur after penetrating abdominal trauma or abdominal surgery. Postoperative PP may or may not indicate leaking anastomoses, since air may be introduced into the peritoneal cavity during surgery . Indeed, PP may be induced intentionally by insufflation of carbon dioxide or helium to facilitate laparoscopic procedures and intraperitoneal chemotherapy . Although such a measure may be contraindicated in patients suffering from cardiorespiratory disorders and increased intracranial pressure  , the presence of gas within the abdominal cavity per se is not detrimental. However, pathological PP as described above is virtually always associated with the presence of pathogens and toxins in the peritoneal cavity. Therefore, it is an indicator of a life-threatening situation that requires emergency surgery.