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

A. Respiratory rate 10/min: Magnesium sulfate can cause central nervous system depression, and respiratory depression is a life-threatening adverse effect. A respiratory rate below 12/min indicates potential magnesium toxicity and requires immediate intervention, making it the priority assessment finding. B. 2+ deep-tendon reflexes: A reflex grade of 2+ is normal and indicates that neuromuscular function is intact. While deep-tendon reflexes are monitored for magnesium toxicity, this finding does not represent an immediate threat. C. 3+ pedal edema: Peripheral edema is a common finding in preeclampsia due to fluid shifts and vascular permeability. While it requires monitoring, it is not immediately life-threatening compared with respiratory depression. D. Urinary output 35 mL/hr: Although reduced urine output can increase the risk of magnesium accumulation, 35 mL/hr is slightly below normal but not critically low. Monitoring is necessary, but the priority remains the depressed respiratory rate.