In mixing insulin with NPH, which step is correct to perform first?

• A. Draw up the correct dosage of NPH insulin into the syringe.
• B. Inject air equal to the amount of NPH insulin prescribed into the vial of NPH insulin.
• C. Inject air equal to the amount of regular insulin prescribed into the vial of regular insulin.
• D. Draw up the correct dosage of regular insulin into the syringe.

Answer: (B)

When mixing two insulins in one syringe, you must manage air pressure in the vials so you can withdraw the correct amounts without cross-contamination. The first step is to inject air into the NPH vial equal to the amount of NPH you plan to draw. This creates space in that vial and prevents a vacuum that could make drawing NPH difficult later. After that, you would inject air into the regular insulin vial for its dose, then draw the regular insulin, and finally draw the NPH insulin. The key is starting with the NPH vial to set up the correct pressure and sequencing for drawing the two insulins.