Final answer:
If a nurse pulls back blood in the syringe while administering meperidine IM, they should withdraw the needle, dispose of the contaminated syringe, and choose a new injection site.
Step-by-step explanation:
If a nurse aspirates and pulls back blood in the syringe while administering meperidine IM in the right deltoid of a client, it means that the needle has punctured a blood vessel, causing blood to enter the syringe. When this happens, the nurse should withdraw the needle immediately and dispose of the contaminated syringe properly. They should then reassess the injection site and choose a new location to administer the medication. It is important to avoid injecting medication into a blood vessel as the medication might not be effective and there can be complications associated with intravascular injection.