Final answer:
The tourniquet should be placed above the site of venipuncture when collecting blood from a vein in the back of the hand. This helps to engorge the veins for easier access. The placement should be about 3 to 4 inches above the puncture site to allow arterial blood flow while obstructing venous flow.
Step-by-step explanation:
When collecting blood from a vein in the back of the hand, the tourniquet should be placed above the site of venipuncture. A tourniquet is typically used in this procedure to engorge the veins, making them easier to access. The pressure from the tourniquet obstructs the venous blood flow which helps to fill and dilate the superficial veins, this does not affect the arterial blood flow into the limb. Therefore, tourniquet placement should be about 3 to 4 inches above the selected puncture site, which is sufficient to engorge the veins while still allowing arterial flow.
The use of a tourniquet is important during venipuncture procedures to provide a clearer view and better access to the veins, thereby increasing the success rate of the procedure. Additionally, the positioning of equipment such as the IV bag in relation to the vein is also a key consideration. For example, IV bags for blood collection are often placed below the donor to facilitate the flow of blood into the bag.