A nurse is assessing a client who is receiving magnesium sulfate for preeclampsia. Which of the following findings is the nurse's priority?

Rationale: A. 2+ deep-tendon reflexes: This is a normal reflex response and indicates that the client is not yet experiencing magnesium toxicity, which would be marked by decreased or absent reflexes. It does not require immediate intervention. B. Respiratory rate 10/min: A respiratory rate below 12/min is a critical indicator of magnesium toxicity. Magnesium sulfate can depress the central nervous system, leading to respiratory depression, which can be life-threatening and demands immediate action. C. Urinary output 35 mL/hr: Although slightly below the typical threshold of 30 mL/hr for safe magnesium clearance, this finding is still adequate. It should be monitored closely but is not the most urgent concern at this moment. D. 3+ pedal edema: Pedal edema is common in preeclampsia due to fluid retention and vascular changes. While notable, it does not take priority over signs of potentially life-threatening respiratory depression.