Which action indicates a need for further teaching when mixing regular insulin and NPH insulin?

When mixing regular insulin and NPH insulin, the correct procedure is to withdraw the regular insulin first before NPH insulin. This is important because regular insulin is a short-acting insulin, while NPH is an intermediate-acting insulin. By withdrawing regular insulin first, you prevent contamination of the regular insulin vial with NPH, which could affect how the short-acting insulin works.

Selecting NPH first would lead to situations where longer-acting insulin could mix with the shorter-acting insulin, potentially causing inconsistencies in dosage and administration. Hence, withdrawing NPH insulin first signifies a misunderstanding of the correct mixing technique, which indicates a need for further education on safe and effective insulin administration practices.

The other actions related to conventional practices regarding air injection into vials are appropriate and necessary steps in the process of administering insulin safely.