Final answer:
The nurse should monitor the client for hypotension when the heart rate is observed to be 140 bpm on the monitor.
Step-by-step explanation:
The nurse should monitor the client for hypotension when the client's heart rate is observed to be 140 bpm on the monitor. Hypotension is characterized by low blood pressure, and a high heart rate can sometimes be a compensatory mechanism in response to low blood pressure. Monitoring for hypotension is important to ensure adequate blood flow and oxygen delivery to the body's organs and tissues.