Final answer:
The nurse should monitor the client for nausea and vomiting.
Step-by-step explanation:
The nurse should monitor the client for nausea and vomiting as a potential side effect of taking ergotamine, a medication used to treat vascular headaches. Ergotamine can cause gastrointestinal symptoms such as nausea and vomiting. While muscle weakness, increased heart rate, and blurred vision can occur with vascular headaches, they are not specific to the medication and do not need to be monitored for specifically in relation to taking ergotamine.