A charge nurse is educating a newly licensed nurse about fluid and electrolyte balance. Which of the following manifestations should the newly licensed nurse identify as a sign of magnesium sulfate toxicity?

A. Bradypnea: Magnesium sulfate toxicity depresses the central nervous system, leading to respiratory depression such as bradypnea. This is a critical sign requiring immediate intervention, as respiratory rates below 12 breaths per minute can be life-threatening. B. Tremors: Tremors are typically associated with hypomagnesemia or withdrawal states, not magnesium toxicity. Magnesium toxicity causes muscle weakness and diminished reflexes rather than increased neuromuscular activity. C. Insomnia: Insomnia is not a recognized symptom of magnesium toxicity. In contrast, elevated magnesium levels tend to cause sedation, lethargy, and decreased mental alertness. D. Hypertension: Magnesium sulfate can actually lower blood pressure due to its vasodilatory effects. Hypertension would be inconsistent with toxicity and more commonly seen in preeclampsia before magnesium is administered.