When performing a lateral decubitus abdomen to visualize air in the peritoneal cavity, which side should be up?

• A. Affected side
• B. Unaffected side
• C. Right side
• D. Left side

Answer: (A)

When performing a lateral decubitus position to visualize air in the peritoneal cavity, the affected side should be up. This is based on the principle that free air will rise to the highest point in the cavity, allowing for better visualization on imaging. If the affected side, where a possible perforation or condition causing air accumulation is located, is facing down, any air present will rise to the opposite side. By keeping the affected side up, the air can accumulate at the highest point, which will be evident in the imaging. This technique is crucial for accurately diagnosing conditions such as free air due to perforated viscera and ensuring optimal diagnostic clarity.