A client presents to the emergency department with symptoms of acute myocardial infarction. After a diagnostic workup, the healthcare provider prescribes a 15 ml intravenous bolus of tPA. Which finding by the nurse indicates the most serious adverse reaction to the drug?

A. Urticaria, itching and flushing: These signs suggest a mild allergic reaction or hypersensitivity, which can occur with thrombolytics like tPA (tissue plasminogen activator). While uncomfortable and needing monitoring, they are not immediately life-threatening. B. Potassium level of 5.5 mEq/L: A slightly elevated potassium level may indicate early hyperkalemia, but it is not a direct or critical adverse effect of tPA. It can be managed with standard interventions and does not pose an immediate life-threatening risk in this context. C. Blood Pressure of 98/60 mm Hg: This is a low-normal reading and might be expected following myocardial infarction. It is not the most serious or urgent adverse effect, unless accompanied by other symptoms like shock or syncope. D. Decreasing level of consciousness: This may indicate intracranial hemorrhage, a rare but life-threatening complication of thrombolytic therapy. It requires immediate provider notification, discontinuation of the drug, and emergency evaluation.