What is the difference between right and left lateral decubitus?

October 1, 2025 •

4 min read

In medical imaging, the lateral decubitus position is a specialized technique used for patients who cannot stand. A fundamental difference exists in how and why clinicians choose between the right and left lateral decubitus positions for specific diagnostic and procedural goals.

Quick Summary

The distinction between right and left lateral decubitus positions is defined by the side the patient lies on, with the choice impacting medical imaging and procedures by leveraging gravity for diagnostic accuracy.

Key Points

Position Definition: The difference between right and left lateral decubitus is the side on which the patient is lying.
Gravity's Role: The choice of position is medically significant because it uses gravity to displace and visualize fluids or air inside the body during imaging.
Left Lateral Benefits: Left lateral decubitus is often preferred for cardiac imaging (less magnification) and for pregnant patients (avoids inferior vena cava compression).
Right Lateral Uses: Right lateral decubitus is used for specific surgical procedures (like on the kidneys) and for diagnosing conditions on the opposite side of the body.
Diagnosis of Effusion/Pneumothorax: For fluid (pleural effusion), the affected side is placed down; for air (pneumothorax), the affected side is placed up.
Patient Safety: Proper technique, including using padding and stabilization, is essential in both positions to prevent patient injury.

The lateral decubitus position is a standard part of medical practice, particularly in radiology, where it provides a specific view of a patient's internal anatomy. The core difference between a right and left lateral decubitus position is simply the side on which the patient is lying. The term "decubitus" refers to lying down, so right lateral decubitus means lying on the right side, and left lateral decubitus means lying on the left side. This seemingly simple choice is critical because gravity influences the movement of fluids and air inside the body, making the specific positioning essential for accurate diagnosis and effective treatment.

Right Lateral Decubitus (RLD) Explained

In the right lateral decubitus position, the patient lies on their right side. This orientation is used for several specific purposes, primarily in diagnostic imaging and surgical procedures.

Applications of Right Lateral Decubitus

Pleural Effusion (right side): For a suspected fluid accumulation in the right lung cavity, the patient is placed in the RLD position. Gravity causes the fluid to settle along the right side, making it more visible on a chest X-ray.
Pneumothorax (left side): If there is a suspected air pocket in the left lung cavity, the RLD position is used. The patient lies on the unaffected (right) side, allowing the air to rise and accumulate along the patient's elevated (left) side, which improves visibility on the radiograph.
Surgical Procedures: This position is common for surgeries involving the thorax, kidneys, or hips, particularly if the procedure is on the patient's left side.
Abdominal Imaging: In specific cases of abdominal imaging, the RLD position may be used to assess the distribution of gas within the stomach and to confirm a diagnosis like gastric volvulus.

Left Lateral Decubitus (LLD) Explained

In the left lateral decubitus position, the patient lies on their left side, with their right side elevated. This is often the more commonly used position for non-urgent procedures due to its physiological benefits.

Applications of Left Lateral Decubitus

Pleural Effusion (left side): When assessing fluid in the left lung cavity, the LLD position is utilized to allow the fluid to pool along the dependent side, making it easier to visualize.
Pneumothorax (right side): For a suspected pneumothorax on the right side, the patient is placed in the LLD position. The unaffected (left) side is down, while the air in the right lung cavity rises to the highest point.
Improved Cardiac Imaging: LLD is often preferred for chest X-rays when imaging the heart and associated structures. With the heart closer to the image receptor, there is less chance for magnification, leading to a clearer image.
Gastrointestinal Health: For some patients, lying on the left side can aid digestion, reduce acid reflux, and relieve pressure on the liver, which is located on the right side of the body.
Pregnancy: This position is especially important for pregnant patients, as it prevents the fetus from compressing the inferior vena cava. This enhances cardiac output and improves blood flow for both the mother and baby.
Minimizing Complications: In critically ill patients, LLD can be used to improve lung function and perfusion, although the benefits can vary by individual.

Key Differences in Application and Effect

The choice between right and left lateral decubitus is not arbitrary; it is a clinical decision based on the specific condition and the goal of the examination or procedure. The fundamental difference lies in how gravity is leveraged to displace internal substances, such as air and fluid.

Comparison of Right vs. Left Lateral Decubitus


Feature	Right Lateral Decubitus (RLD)	Left Lateral Decubitus (LLD)
Patient Position	Lying on the right side	Lying on the left side
Primary Use (Pleural Effusion)	Diagnosing fluid in the right chest cavity	Diagnosing fluid in the left chest cavity
Primary Use (Pneumothorax)	Diagnosing air in the left chest cavity	Diagnosing air in the right chest cavity
Cardiac Imaging	Less common; structures are farther from the image detector	Often preferred; heart is closer to the image detector, reducing magnification
Abdominal Considerations	Used for specific evaluations of gas distribution in the stomach	Can alleviate pressure on the liver and aid digestion
Pregnancy	Avoids compression of the inferior vena cava less effectively than LLD	Recommended to prevent uterine compression of the inferior vena cava
Other Surgical Uses	Used for procedures on the patient's left side (kidney, thorax)	Used in specific procedures like laparoscopic right posterior lobectomy

Considerations for Positioning

Proper positioning in lateral decubitus is crucial for patient safety and comfort, and to ensure the diagnostic accuracy of the procedure. Medical professionals follow specific protocols to achieve this.

Stability: The patient must be stabilized to prevent rolling, often using pillows or supports between the knees and behind the back.
Padding: Pressure points, such as the axilla, iliac crest, and knees, are padded to prevent pressure injuries and nerve damage.
Timing: For imaging of air or fluid, the patient must be kept in the decubitus position for at least five minutes before the image is taken to allow internal contents to settle due to gravity.
Airway Management: In a surgical setting, access to the airway and proper patient alignment are critical.

Conclusion

In summary, the difference between right and left lateral decubitus is determined by the patient's dependent side. This positional choice is far from arbitrary; it is a critical tool in medicine that leverages gravity to enhance visibility during imaging and to optimize patient outcomes during specific procedures. The specific side chosen depends entirely on the clinical objective, whether it's to visualize free-flowing fluid or air, optimize cardiac imaging, or ensure comfort and safety for conditions like pregnancy. Proper patient positioning is a foundational aspect of safe and effective medical care. For more on surgical positioning, read about proper patient positioning guidelines based on information from the AliMed Blog.

Frequently Asked Questions

The primary purpose is to use gravity to diagnose conditions like pleural effusion (fluid in the chest cavity) and pneumothorax (air in the chest cavity), especially in patients who cannot stand.

To visualize a suspected pneumothorax on the right side, a left lateral decubitus X-ray is performed with the patient lying on their left (unaffected) side. This allows the air to rise to the patient's right side, making it easier to see on the image.

The left lateral decubitus position is preferred for pregnant women because it helps prevent the uterus from compressing the inferior vena cava, which improves blood flow and cardiac output for both mother and fetus.

Yes, patients should be prepared by removing any jewelry or opaque objects from the area to be imaged. For imaging purposes, the patient must often be kept in the position for several minutes to allow air and fluid to settle.

The right lateral decubitus position is commonly used for surgical procedures involving the thorax, kidney, or hip, especially when the surgery is performed on the patient's left side.

Proper padding is crucial to protect pressure points like the shoulders, hips, and knees from potential injuries, nerve damage, and reduced blood flow, particularly during longer procedures.

Yes, lateral decubitus positioning can be used for abdominal X-rays, especially for patients unable to stand. The specific side used can help highlight different structures or confirm conditions like abdominal free air.