What is the primary purpose of using a tourniquet during venipuncture?

The primary purpose of using a tourniquet during venipuncture is to restrict venous blood flow. By applying a tourniquet above the site where the needle will be inserted, it occludes the veins in the area, allowing the blood to pool in the veins. This distension makes the veins more prominent and easier to locate and puncture.

The process of restricting blood flow, combined with the natural response of veins to this occlusion, helps the healthcare professional successfully access a vein for blood draws or infusions. It's important to release the tourniquet once access is achieved to restore normal blood flow and minimize discomfort for the patient.

Other options, such as calming the patient or enhancing blood clotting, do not accurately describe the primary function of a tourniquet. While ensuring a patient is calm is always beneficial and easier access can help with needle penetration, those are secondary to the main goal of using a tourniquet in this context.