A 65-year-old patient with a history of uncontrolled high blood pressure presents for an emergency dental appointment. Which preventive agent is safe for this patient?

The use of oxygen as a preventive agent for this patient is safe due to its non-invasive nature and the fact that it does not interact negatively with high blood pressure. Oxygen therapy is often used in various medical situations, including emergency settings, to ensure adequate oxygenation, especially in patients who may be in respiratory distress or have other systemic health concerns.

This is especially relevant for a patient with a history of uncontrolled high blood pressure, who may be sensitive to certain drugs or agents that could exacerbate their condition. In contrast, other options may carry risks: nitrous oxide can cause a temporary increase in blood pressure or anxiety, fluoride rinses might not directly address the emergency needs of the patient, and local anesthetics containing epinephrine can also elevate blood pressure due to the vasoconstrictive effects of epinephrine, making them less ideal for someone with a history of hypertension.