The nurse administers a sublingual nitroglycerin tablet to a client with unstable angina. Which finding is most important for the nurse to report to the healthcare provider (HCP)?

A. Bilateral tinnitus when initially standing up: Tinnitus is not a common or serious adverse effect of nitroglycerin. While it may indicate another underlying issue, such as hypertension or ototoxicity, it is not immediately life-threatening. B. Dizziness when rising from the bedside: Dizziness can result from the vasodilatory effects of nitroglycerin causing orthostatic hypotension. It is relatively common and usually managed with safety precautions and monitoring rather than immediate reporting. C. Hypotension with a systolic of 90 mm Hg: A systolic blood pressure of 90 mm Hg is concerning after nitroglycerin administration, as the drug significantly lowers preload and can precipitate hemodynamic instability. This finding requires prompt HCP notification to prevent complications such as syncope or myocardial underperfusion. D. Onset of headache after administration: Headache is a well-known and expected side effect of nitroglycerin due to cerebral vasodilation. While uncomfortable, it is generally benign and does not warrant immediate reporting unless it becomes severe or unrelenting.