Which intervention is critical when a patient is experiencing lightheadedness from atenolol?

When a patient experiences lightheadedness from atenolol, checking blood pressure is critical because atenolol is a beta-blocker that can lower heart rate and blood pressure. Lightheadedness in this context may indicate hypotension (low blood pressure), which can occur as a side effect of the medication. Monitoring blood pressure allows for an assessment of the patient's hemodynamic stability and helps determine if adjustments in medication or additional interventions are necessary.

Providing fluids and electrolytes might help if the lightheadedness were due to dehydration, but it does not address the direct effects of the medication on blood pressure. Administering vitamin C is unrelated to the management of lightheadedness or older adult medication adjustments, and encouraging physical activity could worsen symptoms if the patient is experiencing significant dizziness or hypotension. Therefore, assessing blood pressure is the most relevant and critical intervention in this scenario.