Final answer:
The nurse should instruct the client to withhold digoxin for 48 hours prior to cardioversion because it can affect the heart rhythm and interfere with the procedure.
Step-by-step explanation:
The nurse should instruct the client to withhold digoxin for 48 hours prior to cardioversion. Digoxin is a medication used to treat certain heart conditions, but it can affect the heart rhythm and interfere with the effectiveness of cardioversion. Withholding digoxin helps ensure the accuracy and safety of the procedure.