Final answer:
For an IM injection in an obese patient, a longer needle should be used to reach the muscle mass and inserting the needle at a 90-degree angle is optimal. The deltoid muscle may not be the best site and needle gauge is chosen based on medication viscosity.
Step-by-step explanation:
When a nurse is preparing to administer an IM injection to a client who is obese, the appropriate action would be to use a longer needle for the injection. This is necessary to ensure that the medication is delivered into the muscle mass, beyond the adipose tissue layer. It is also recommended to insert the needle at a 90-degree angle to ensure proper needle depth. Administering the injection in the deltoid muscle may not be suitable for an obese client if the adipose tissue is too thick, and a site like the ventrogluteal or dorsogluteal may be more appropriate. A smaller gauge needle is typically not necessary and the gauge size is selected based on the viscosity of the medication being administered, not the size of the patient.