How is pneumoperitoneum most reliably detected in an unstable patient?

How is pneumoperitoneum most reliably detected in an unstable patient?

• A. Free intraperitoneal air on upright radiographs or CT
• B. Abdominal ultrasound
• C. MRI
• D. Lateral decubitus radiographs

Answer: (A)

In a patient who is unstable, you want the imaging method that most reliably shows free air in the peritoneal cavity to guide urgent management. Free intraperitoneal air rises and collects under the diaphragms, so an upright radiograph of the chest/abdomen can reveal air outlining the under-surface of the diaphragm—this finding is highly specific for pneumoperitoneum. If the patient can be transported and stabilized enough for it, computed tomography is even more sensitive and can detect very small amounts of free air and precisely localize its source, while also identifying other injuries. Ultrasound is fast and portable but far less reliable for detecting small volumes of free air and is highly operator-dependent. MRI is impractical in an emergent setting due to time, availability, and the need for patient stability. If upright imaging isn’t possible, a lateral decubitus radiograph can still show free air, but it’s not as reliable as an upright view or CT.

In a patient who is unstable, you want the imaging method that most reliably shows free air in the peritoneal cavity to guide urgent management. Free intraperitoneal air rises and collects under the diaphragms, so an upright radiograph of the chest/abdomen can reveal air outlining the under-surface of the diaphragm—this finding is highly specific for pneumoperitoneum. If the patient can be transported and stabilized enough for it, computed tomography is even more sensitive and can detect very small amounts of free air and precisely localize its source, while also identifying other injuries.

Ultrasound is fast and portable but far less reliable for detecting small volumes of free air and is highly operator-dependent. MRI is impractical in an emergent setting due to time, availability, and the need for patient stability. If upright imaging isn’t possible, a lateral decubitus radiograph can still show free air, but it’s not as reliable as an upright view or CT.