Procedures · Chest, abdomen and GI2 min read5-question check
AP and decubitus chest
AP chest: CR 3 to 4 inches below the jugular notch. Decubitus: fluid side down, air side up.
Patient and part
The AP chest is for patients who cannot stand, usually supine or semi-erect on a stretcher or in bed with a mobile unit. Sit the patient as upright as the condition allows, because erect lets the diaphragm drop, and with a horizontal beam it can show air-fluid levels. Place the receptor behind the patient, centered to the chest, with the top about 2 inches above the shoulders. Roll the shoulders forward if the patient can, and make sure the chest is not rotated on the mattress.
Central ray
Center the central ray 3 to 4 inches below the jugular notch, which is about the level of T7. Angle it caudad until it is perpendicular to the sternum, usually about 3 to 5 degrees. This keeps the clavicles from projecting over the apices and gives a truer picture of the lungs. Use 72 inches when the room allows; at a shorter distance the heart magnifies more.
What a good image shows
Expect a different-looking image. The heart sits farther from the receptor, so it appears larger than on a PA. A supine patient cannot inspire as deeply, so fewer posterior ribs show above the diaphragm, often fewer than 10. No rotation still means the medial clavicles are equidistant from the spine. Mark the image AP and supine or semi-erect.
Decubitus chest
A lateral decubitus chest uses a horizontal beam with the patient lying on one side, giving an AP or PA projection. For fluid, such as a pleural effusion, put the affected side down so the fluid layers along the lateral chest wall. For air, such as a small pneumothorax, put the affected side up so the air rises. Raise both arms over the head, place the patient on a radiolucent pad so the down side is fully included, and wait at least 5 minutes before exposure so fluid settles and air rises. Center at T7 and include both lungs.
Clinical Example
A patient with a suspected right pleural effusion cannot stand. You place her in a right lateral decubitus, lift her on a firm pad, raise her arms, and wait 5 minutes. With the horizontal beam, the fluid layers clearly along the right lateral chest wall.
Common Mistakes
- Using a vertical beam on a supine patient and expecting to see an air-fluid level.
- Putting the affected side down when looking for a pneumothorax.
- Leaving the patient flat on the mattress so the down-side lung is cut off.
- Forgetting to mark the image AP and supine or semi-erect.
Why It Matters
Portable and decubitus chests serve the sickest patients, often in the ICU. The registry asks which side goes down, where to center, and why the heart looks larger on an AP.
Key Relationships
- AP chest: CR 3 to 4 inches below the jugular notch, angled 3 to 5 degrees caudad
- AP versus PA: heart magnified, fewer ribs shown
- Fluid: affected side down; air: affected side up
- Air-fluid levels require a horizontal beam
- Wait at least 5 minutes in position before a decubitus exposure