Subjects who undergone abdominal intervention and reported major symptoms and signs suggestive of gastrointestinal perforation (abdominal pain, leukocytosis, fever) within the third postoperative day.

Exclusion criteria: inability to consent to the study, age ≤18 yr, certain or probable pregnancy, inability to remain in upright position for more than 10 minutes.

All enrolled patients underwent erect chest x-rays assessment. In all cases the diagnosis of pneumoperitoneum was based upon the plain film identification of subdiaphragmatic air on the upright posteroanterior chest radiograph.

All patients were transported from their hospital rooms to the radiology department in wheelchairs and remained in an upright position for more than 10 min before the chest radiographs were obtained. In all cases upright posteroanterior was obtained with the patient standing, using 183-cm distance, 125 kVp, phototimed exposure, and radiographic film with a wide exposure latitude.

The disappearance of intraabdominal free gas will be evaluated every 48h and will be defined as the loss of the

• Prediction of the presence of gastrointestinal perforation by the finding of intra-abdominal free air on a chest radiograph after abdominal surgery

The evaluation of time taken for the absorption of intra-abominal free air and its correlation with age, sex, body mass index, previous surgery, operative time, type of surgery and use of peritoneal drainage tubes.

The disappearance of intra-abdominal free gas was defined as the loss of the gas bubble under the domes of the hemidiaphragms on an erect chest radiograph