Before administering a second sublingual nitroglycerin tablet for chest pain, which vital sign must the nurse check first?

When considering the administration of a second sublingual nitroglycerin tablet for chest pain, it is crucial to assess the patient's blood pressure prior to giving the medication. Nitroglycerin is a vasodilator that acts to widen blood vessels, which can significantly lower blood pressure. If the patient's blood pressure is already low, administering another dose of nitroglycerin could lead to complications such as hypotension, which can be dangerous.

Monitoring the blood pressure ensures that the nurse evaluates whether the patient is stable enough for additional doses. This step is essential in preventing adverse effects and maintaining patient safety. While other vital signs, such as temperature, respirations, and pulse rate, provide valuable information about the patient's overall condition, they do not directly relate to the immediate effects of nitroglycerin and the potential risks associated with its administration. Thus, checking blood pressure is the most critical action before proceeding with the second dose.