it seems that the inclusion of a us examination to the e - fast method in order to detect free gas in the peritoneal cavity is justified since it is a sign of gastrointestinal perforation , and is clinically as relevant as the presence of free fluid . the authors do not report any financial or personal links with other persons or organizations , which might negatively affect the content of this publication and claim authorship rights to this publication .
in most cases , pneumoperitoneum is caused by gastrointestinal perforation , which usually requires surgical treatment . 
 many authors believe that ultrasound imaging of pneumoperitoneum is at least as effective as conventional radiography , or even that its efficacy is superior . 
 in such a situation , it is imperative to make this modality one of the main tools in the diagnostic arsenal of emergency medicine . 
 this is the main aim of this paper . 
 first , ultrasound anatomy of so - called thoracic - abdominal border is discussed . 
 the equipment requirements emphasize that the diagnostic process can be conducted with the simplest portable us scanner , even without the doppler mode . 
 the technique of a us examination , the aim of which is to detect , free air in the peritoneal cavity is also simple and conducted with the patients lying down , either in the supine or lateral position . 
 a convex transducer with the frequency of 3.55 mhz is applied above the lower intercostal spaces on the right and left side , to the epigastric region below the xiphoid process and in various sites of the abdominal wall . 
 the most effective examination , however , is conducted in the left lateral position via the right intercostal spaces . 
 the differential diagnosis on the right side under the diaphragm should include the presence of a subdiaphragmatic abscess with gas and a hepatic abscess with a similar content as well as transposition of the colon in between the diaphragm and the liver ( chilaiditi syndrome ) . 
 it seems that the inclusion of a us examination to the e - fast method in order to detect free gas in the peritoneal cavity is justified since it is a sign of gastrointestinal perforation in numerous cases , and is clinically as relevant as the presence of free fluid .