Final answer:
Among the symptoms listed, a respiratory rate of 8 breaths per minute is an indication of magnesium toxicity and would require immediate intervention.
Step-by-step explanation:
A nurse is tasked with monitoring a client in preterm labor who is receiving magnesium sulfate via continuous IV infusion. Among the symptoms listed, respiratory rate of 8 breaths per minute is a significant indicator of magnesium toxicity. Magnesium sulfate is used to treat or prevent seizures in women with eclampsia but must be carefully monitored due to its potential side effects, including magnesium toxicity. Hypotension can also be associated with magnesium toxicity, but a respiratory rate as low as 8 breaths per minute is particularly concerning and requires immediate medical attention. Urinary retention and increased deep tendon reflexes are typically not associated with magnesium toxicity.