Final answer:
The tourniquet is applied to the upper arm, above the antecubital region where venipuncture will occur, to enhance venous visibility, making the median cubital vein a suitable site for drawing blood.
Step-by-step explanation:
When draining a vein in the antecubital region, the tourniquet is applied to the upper arm, typically about 3 to 4 inches above the site where the venipuncture will be performed. The tourniquet is wrapped snugly to impede venous flow while still allowing arterial blood to enter the limb, which causes the veins to become more pronounced, thereby facilitating the venipuncture. It is important to place the tourniquet at the correct level and to ensure that it is not left on for an excessively long time to prevent discomfort and potential complications.
The median cubital vein, a superficial vessel located in the antecubital region that links the cephalic vein to the basilic vein, is a frequent site from which to draw blood, due to its accessibility. Care must be taken to apply the tourniquet properly so as not to cause undue harm and to ensure that the vein can be punctured successfully for the purpose of blood draw or intravenous therapy.