When assessing ascites by percussion, what is the purpose of having the patient turn onto one side?

The purpose of having the patient turn onto one side during the assessment of ascites by percussion is to test for shifting of dullness. When a patient is placed in a lateral decubitus position, any fluid that may be present in the abdominal cavity will settle toward the dependent side, allowing the physician or healthcare provider to assess the presence of free fluid more effectively.

In this position, percussion can reveal a shift from tympanic sound to dullness on the side where the fluid accumulates. When the patient is subsequently placed back in a supine position and percussion is performed again, a change in the area of dullness can be noted, indicating the presence of fluid, as opposed to the normal resonant sounds of the intestines or air-filled structures. This shift is a classic sign used in clinical practice to confirm ascites.

The other options provide alternative scenarios, but they do not address the core reason for changing the patient's position for the purpose of diagnosing ascites.