Final answer:
The nurse should anchor the vein by placing a thumb below the insertion site and apply a tourniquet to aid in palpating the vein, while keeping the angle of insertion between 15 to 30 degrees.
Step-by-step explanation:
The action a nurse should perform to best ensure effective insertion of a venous access device into a patient's arm is to anchor the vein by placing a thumb 1 to 2 inches below the puncture site. This technique prevents the vein from rolling and provides stability, which facilitates the insertion of the needle. Additionally, applying a tourniquet 8 to 12 inches above the insertion site can help distend the vein, making it more palpable and easier to access. However, the needle should be inserted at a low angle to the skin, typically 15 to 30 degrees, not at 45 degrees as stated in option B. Option C is not specific to the moment of insertion, and option D is a method related to measuring blood pressure rather than inserting an IV.