Final answer:
The nurse should administer Flumazenil to reverse the respiratory depression caused by midazolam, as it is a benzodiazepine antagonist suitable for this situation.
Step-by-step explanation:
If a client who is receiving moderate (conscious) sedation with midazolam has a decreased respiratory rate from 16/min to 6/min and a drop in oxygen saturation from 92% to 85%, the nurse should administer Flumazenil. Midazolam is a benzodiazepine, and Flumazenil is an antagonist that reverses the effects of benzodiazepines, including respiratory depression. Naloxone is used to reverse opioid overdose, Atropine is used for bradycardia (not respiratory depression), and Epinephrine is used for severe allergic reactions and cardiac arrest.