The right lateral decubitus position means lying on your right side. “Lateral” refers to the side, “decubitus” comes from a Latin word meaning to lie down, and “right” specifies which side is against the surface beneath you. In medical settings, this position is used for specific imaging studies, surgical procedures, and digestive assessments, and it has distinct effects on your organs depending on how gravity shifts their weight and position.
How the Position Works
When you lie on your right side, gravity pulls your internal organs toward the right. Your right lung, which sits lower, gets compressed by the weight of the structures above it, including the heart and the tissue between your lungs. Meanwhile, your left lung sits higher and expands more freely. Blood flow also shifts downward, increasing circulation to the right lung while decreasing it on the left side. This redistribution of air and blood is one reason the position matters so much in medicine: it changes how your lungs, heart, stomach, and major blood vessels function, sometimes in helpful ways and sometimes not.
Lung Function and Breathing
In the right lateral decubitus position, the right lung (now the “dependent” lung, meaning the one closest to the ground) receives more blood flow due to gravity. At the same time, the weight of the liver and the heart’s surrounding structures compresses it, which can reduce how much air it takes in. Research shows that ventilation shifts toward whichever lung is lower, but this compression from adjacent organs can create a mismatch between airflow and blood flow. In healthy people this effect is minor, but for someone with lung disease, the position choice can meaningfully affect oxygen levels.
Detecting Fluid in the Chest
One of the most common medical uses for the right lateral decubitus position is chest X-rays designed to find fluid around the lungs, known as pleural effusion. When you lie on your right side, any free-flowing fluid in the right chest cavity settles along the lowest point, creating a visible horizontal line on the X-ray. If the fluid flows freely and creates a smooth, complete line from the diaphragm to the top of the chest, doctors can confirm there are no adhesions (areas where the lung lining has stuck together). An irregular or segmented line suggests the fluid is trapped in pockets. In one study of 66 patients, about 39% showed a smooth, complete fluid line indicating freely moving fluid, while roughly 61% showed an irregular pattern pointing to loculated (trapped) collections.
Stomach Emptying and Digestion
Your stomach’s natural anatomy makes the right lateral decubitus position particularly useful for digestion. The stomach’s outlet, called the pylorus, sits on the right side of your body. When you lie on your right side, gravity helps move food toward this exit and into the small intestine. Studies in infants found that gastric emptying at 60 minutes in the supine (flat on the back) position averaged only 35%, but after switching to the right lateral position, emptying jumped to 60% by 90 minutes. Many patients who initially appeared to have delayed stomach emptying showed significant improvement simply by changing position, which is why some imaging centers routinely add right-side-down views to their stomach emptying studies.
This same anatomical feature creates a downside for acid reflux. When you lie on your right side, the stomach sits above the junction where it connects to the esophagus. If the muscular valve between the two is weak or relaxed, stomach acid flows more easily upward into the esophagus. A meta-analysis found that sleeping on the right side significantly increased acid exposure time compared to sleeping on the left side, with a mean difference of about 2% more acid contact time. That may sound small, but for people with gastroesophageal reflux disease, it translates into noticeably more heartburn and reflux episodes overnight.
Surgery and Procedural Access
Surgeons use the right lateral decubitus position when they need access to the left side of the body, particularly for kidney operations, certain spinal procedures, and lung surgeries. Placing the patient on their right side opens up the left flank and ribcage area for the surgical team. The reverse is also true: left lateral decubitus (lying on the left side) is used for right-sided access. For laparoscopic surgeries, this positioning allows a combined approach from both the front and back of the body. Surgeons have reported using this technique successfully for kidney removal and lymph node procedures, finding it both safe and effective for reaching structures that would be difficult to access with the patient lying flat.
For colonoscopies, starting in the right lateral position rather than the traditional left lateral position has been studied in randomized trials. A meta-analysis of five trials with over 800 participants found no significant difference between the two positions in terms of how quickly the scope reached the end of the colon, the overall success rate of the procedure, or patient discomfort. In practice, most colonoscopies still begin with the patient on their left side, but the right side is a viable alternative when needed.
Pregnancy and Blood Flow
During late pregnancy, lying flat on your back can compress a major vein (the inferior vena cava) that returns blood from your lower body to your heart. The growing uterus presses down on this vessel, potentially reducing blood flow to both the mother and baby. Left-side lying has long been the standard recommendation to relieve this compression, and MRI-based research supports it: at a 30-degree left-side tilt, the volume of the inferior vena cava was significantly larger than at either a 15- or 30-degree right-side tilt. In 70% of pregnant women studied, the 30-degree left tilt produced the best blood flow through this vein.
Interestingly, about 23% of the women in the study actually had the best vena cava volume in the 30-degree right-side tilt position. At a gentler 15-degree angle, there was no statistically significant difference between left and right tilting. So while left-side sleeping remains the go-to recommendation during pregnancy, the right lateral position is not universally harmful, and individual anatomy plays a role.
Heart Imaging
Echocardiograms, the ultrasound tests used to visualize the heart, are typically performed with the patient lying on their left side. This shifts the heart closer to the chest wall, making it easier for the ultrasound probe to capture clear images. However, when an ultrasound probe is passed through the esophagus (a transesophageal echocardiogram), the right lateral decubitus position produces comparable image quality to the left. One notable difference: blood flow velocities in the right pulmonary vein change depending on which side is down. Peak flow in that vein dropped from about 48 cm/s in the right lateral position to 38 cm/s in the left lateral position, reflecting how gravity shifts blood distribution between the lungs. For most diagnostic purposes, though, either position works.