Final answer:
The nurse should assess the client's deep tendon reflexes and level of consciousness due to the potential risk of magnesium toxicity indicated by the elevated magnesium level.
Step-by-step explanation:
Based on receiving a laboratory report stating that a client receiving magnesium sulfate 2 g/h IV for preeclampsia has a magnesium level of 6.4 mEq/L (0.30 mmol/L), the nurse should assess the client's deep tendon reflexes and level of consciousness. These assessments are crucial because they can indicate signs of magnesium toxicity, which is a critical situation. If either deep tendon reflexes are absent or the level of consciousness is decreased, the healthcare provider should be notified immediately, and the magnesium sulfate infusion should be stopped.