Final answer:
The nurse needs to monitor the client's blood pressure because most antipsychotic medications cause wide fluctuations in blood pressure throughout the day.
Step-by-step explanation:
The nurse needs to monitor the client's blood pressure because most antipsychotic medications cause wide fluctuations in blood pressure throughout the day. This is known as orthostatic hypotension, which means that blood pressure goes below the homeostatic set point when the client changes positions. Monitoring the blood pressure will help the nurse identify any abnormal fluctuations and take appropriate action to manage this side effect.