Which of the following is a sign that a vein has collapsed during venipuncture?

A collapsed vein during venipuncture is characterized by certain physical signs, one of which includes visible swelling at the puncture site. This occurs when the pressure within the vein decreases significantly, often resulting in the vein becoming flattened. When the vein collapses, blood flow is disrupted, leading to an accumulation of blood in the surrounding tissue, which manifests as swelling or hematoma in the area.

The other options do not accurately reflect signs of a collapsed vein. Increased blood flow would suggest that the vein is functioning properly, while uneven pressure during a blood draw could signal other issues but not necessarily that the vein has collapsed. Blood returning to the tube typically indicates that blood is flowing correctly from the vein. Thus, recognizing visible swelling at the puncture site is key in identifying a collapsed vein during the venipuncture process.