Abdomen (lateral decubitus view)

The lateral decubitus abdominal radiograph is used to identify free intraperitoneal gas (pneumoperitoneum). It can be performed when the patient is unable to be transferred to, or other imaging modalities (e.g. CT) are not available. The most useful position for detecting free intraperitoneal air is the left lateral decubitus position.

Indication

To assess for a pneumoperitoneum when other imaging modalities are unfeasible for technical or availability reasons.

Patient position

• the patient is lying on either the left (left lateral decubitus) or right (right lateral decubitus) side

  • the left lateral decubitus is preferred as any free intraperitoneal gas will be contrasted by the liver

  • having a radiolucent sponge to elevate the patient's downside may ensure the entire abdominal region is captured well

• the detector can be placed anteriorly or posteriorly

• patient's hands should be raised to avoid superimposing on the region of interest; legs may be flexed for balance

• rotation of shoulders or pelvis should be minimized, but not as critical as on other abdominal radiographic views

• patients should be changed into a hospital gown, with radiopaque items (e.g. belts, zippers) removed

• x-ray is often performed on expiration however this will depend on department protocols 

Technical factors

• lateral decubitus

• centering point

  • midsagittal place (xiphisternum) just superior to the iliac crest

• collimation

  • laterally to the elevated lateral abdominal wall (e.g. right side for a left lateral decubitus x-ray)

  • superior to the diaphragm

  • inferior to the inferior pubic rami

• orientation

  • portrait

• detector size

  • 35 cm x 43 cm

• exposure

  • 70 - 80 kVp

  • 30 - 120 mAs

• SID

  • 100 cm

• grid

  • yes

Image technical evaluation

• it is essential that the elevated lateral abdominal wall is included on the image to detect any free intraperitoneal gas.

• there should be no blurring of the bowel gas due to respiratory motion.

Practical points

These x-rays are often performed as mobile examinations as the patient is too unwell to travel to the radiology department.

The lateral decubitus x-ray may be more useful than the PA erect view for detecting intraperitoneal free gas ¹.