Pneumoperitoneum could be due to life threatening conditions and its quickly diagnosis is important in the emergency department (ED). Signs and symptoms are non-specific and radiography has low accuracy in the acute setting. Computed tomography (CT) is considered the gold standard, however it is not a cost-effective option in the vast population of patients with abdominal pain. Ultrasonography is able to detect as little as 2 ml of free air, however diagnostic accuracy of ultrasonography remains unclear. This study evaluates the accuracy of ultrasonography for the diagnosis of pneumoperitoneum, the most accurate abdominal scan and the most accurate echographic sign for the detection of free air.

Methods Consecutive patients presenting to ED for acute abdominal pain and with a diagnosis of pneumoperitoneum at CT or at surgery (study group) and a similar number of patients without a diagnosis of pneumoperitoneum (control group) undergo abdominal ultrasonography in a standardized protocol that include 10 scans for each patient registered on a video of 5 seconds. The videos are randomly reviewed by 4 sonographers and by 2 physicians with no experience in ultrasonography blind to final diagnosis and to all clinical data with the aim of detecting for each scan pneumoperitoneum. Accuracy of ultrasonography for the diagnosis of pneumoperitoneum will be calculated considering CT or surgery as gold standard. Furthermore intra and interobserver agreement and the accuracy of each ultrasonographic sign and scan will be calculated.

Inclusion Criteria:

• All patients more than 18 years with acute abdominal pain

Exclusion Criteria:

• Refused consent
• Less than 18 years old
• Not possible to perform ultrasonography

Patients more than 18 years presenting to emergency departments with acute abdominal pain and clinical suspected pneumoperitoneum