Final answer:
The LPN should notify the registered nurse immediately if the pregnant client with preeclampsia receiving magnesium sulfate exhibits an RR of 10 breaths per minute.
Step-by-step explanation:
When assisting in the care of a pregnant client with preeclampsia receiving magnesium sulfate, the licensed practical nurse (LPN) should notify the registered nurse immediately if a sign of magnesium toxicity is noted. In this case, the LPN should be concerned if the client exhibits an RR of 10 breaths per minute as this is a potential indicator of magnesium toxicity.