The nurse is caring for a client with an order for regular insulin and neutral protamine Hagedorn (NPH) insulin. When mixing the insulins in a single syringe, which action by the nurse is correct?

A. The nurse injects air into the regular insulin vial first: Air should be injected into each vial before drawing insulin to prevent creating a vacuum, but the order of air injection does not override the critical rule regarding drawing up insulin. The sequence of drawing the insulins is more important to maintain correct dosing. B. The nurse withdraws the NPH insulin first: When mixing insulins, rapid-acting or short-acting insulin (e.g., regular insulin) should be drawn up first to avoid contaminating it with NPH, which could alter the onset and peak of the short-acting insulin. Drawing NPH first is incorrect practice. C. The nurse gently rotates the NPH insulin vial: NPH insulin is a suspension that must be gently rolled to mix the insulin evenly before drawing it into the syringe. This ensures accurate dosing and prevents inconsistent absorption and unpredictable blood glucose effects. D. The nurse selects a 3 mL syringe to mix insulins: While syringe size should match the insulin dose for accuracy, selecting a 3 mL syringe is not specific to the proper technique of mixing insulins and is less critical than ensuring proper vial mixing and correct order of withdrawal.