A nurse is preparing to administer 10 units of regular insulin and 20 units of NPH insulin to a client who has diabetes mellitus. When mixing the two types of insulin, which of the following actions should the nurse take first?

A. Inject 20 units of air into the NPH insulin vial: When mixing regular insulin and NPH insulin, the first step is to inject air into the NPH vial (the cloudy insulin) to equalize the pressure in the vial. This prevents contamination of the regular insulin vial with NPH insulin and ensures accurate dosing. B. Withdraw 10 units of insulin from the regular insulin vial: Withdrawing insulin from the regular insulin vial should be done after the air is injected into both vials. First, you inject air into the NPH vial and then into the regular insulin vial before drawing up the insulin. C. Replace the needle for withdrawal with a safety needle: There is no need to replace the needle unless it is contaminated or dull. You should be able to use the same needle for both drawing air and insulin. D. Inject 10 units of air into the regular insulin vial: Injecting air into the regular insulin vial first could risk contamination of the regular insulin with NPH insulin when the NPH insulin is withdrawn.