Final answer:
The nurse should notify the healthcare provider first if the client's DTRs are observed to be decreased while receiving mag sulfate IV, as this could be a sign of magnesium sulfate toxicity.
Step-by-step explanation:
If the nurse assesses that the client's deep tendon reflexes (DTRs) are decreased while receiving mag sulfate IV, the first action the nurse should take is b) Notify the healthcare provider. Decreased DTRs may be an indication of magnesium sulfate toxicity, and it is important for the healthcare provider to be informed so that appropriate interventions can be initiated. Administering a bolus of magnesium sulfate (a) or increasing the infusion rate (c) may worsen the client's condition. Administering calcium gluconate (d) may be considered to counteract the effects of magnesium sulfate toxicity, but consulting with the healthcare provider should be the first step.