Pneumoperitoneum

This disorder has been observed with pulmonary barotrauma, with movement of air from a ruptured pulmonary bulla dissecting along the mediastinum to the retroperitoneal area, and then released into the peritoneum, to track under the diaphragm. It is also possible that previous injury to the lung or diaphragm, producing adhesions, could permit the direct passage of air from the lung to the subdiaphragmatic area.

Another possible cause of pneumoperitoneum is, as described earlier, a rupture of a gastrointestinal viscus, especially with barotrauma of ascent or underwater explosions.

The condition may be detected by chest x-ray study or positional abdominal x-ray study (gas under the diaphragm, in the erect position).
Treatment is by administration of 100 per cent oxygen with a non-pressurized technique. Usually, complete resolution occurs within hours. Management of the cause (pulmonary or gastrointestinal) is required, and surgical management of a ruptured gastrointestinal viscus may be needed.