The nurse should prepare a total of 42 units of insulin in the syringe.
The calculation is as follows:
14 units of regular insulin + 28 units of NPH insulin = 42 units total
The nurse will mix these two types of insulin in the same syringe, following the proper procedure for drawing up and administering mixed insulin doses. The regular (short-acting) insulin should be drawn up into the syringe first, followed by the NPH (intermediate-acting) insulin to prevent contamination of the regular insulin vial with NPH insulin. This is because regular insulin can be given intravenously, but NPH insulin cannot. If contamination were to occur, it could potentially create issues if that regular insulin were later used for an IV.