Point of Care Ultrasound for Diagnosis of Abdominal Free Air

Free peritoneal air is a marker of potential intraabdominal catastrophe, reflecting perforation of a hollow viscous organ such as stomach or intestine. While definitively identified by computed tomography, this diagnostic test can be delayed. Presence of air beneath the diaphragm on an upright chest or abdominal radiograph can allow for faster diagnosis, but again can present limitations in terms of timing. Bedside clinician performed ultrasound has become standard practice in emergency medicine and critical care settings. Traditionally, air is not conducive to diagnostic ultrasound, but the artifacts it creates can be used to give clues about certain conditions. Recently this artifact has been proposed as a means to identify free peritoneal air. Several small studies have shown promise for the technique, but further investigation is warranted. In this study the investigators will generate a database of standardized abdominal ultrasound images in subjects undergoing laparoscopic surgery. During this surgery, the peritoneal cavity is intentionally insufflated with air. The majority of this is removed at the end of the case, but small volumes of air remain, as evidence by the presence of air on CT scan when performed shortly after surgery. The investigators will obtain a standardized set of images preoperatively and post operatively which will then be reviewed in a blinded fashion by three expert reviewers, one each from radiology, surgery and emergency medicine, with data analysis to determine sensitivity and specificity of ultrasound for free air.