Final answer:
The nurse should monitor the patient's blood pressure after administering a beta blocker and an antihypertensive drug during a procedure under general anesthesia, as these medications can cause hypotension.
Step-by-step explanation:
When a patient receives a beta blocker and an antihypertensive drug during a procedure, the primary physiological variable a nurse should monitor is blood pressure. Beta blockers can cause a decrease in heart rate and blood pressure by blocking the effects of adrenaline on the heart. Antihypertensive drugs are used to lower high blood pressure and can further contribute to lowering blood pressure. It is essential to monitor blood pressure to ensure it remains within a safe range during the procedure, as both medications can cause hypotension (abnormally low blood pressure), which can lead to dizziness, fainting, or even shock.