Final answer:
The nurse should administer Naloxone to the patient experiencing respiratory depression from an overdose of morphine, as it is designed to reverse the effects of opioids.
Step-by-step explanation:
A nurse is assessing a client who is receiving morphine IV bolus for pain following a cesarean birth. When the nurse notices a respiratory rate of 8/min, which is below the normal range and indicates respiratory depression, a side effect of opioid medications such as morphine, the appropriate action is to administer an opioid antagonist. Of the options provided, Naloxone is the medication specifically designed to reverse the effects of opioids, including respiratory depression caused by an overdose. Therefore, the nurse should administer Naloxone (Option 4) to the patient. Fentanyl, another opioid analgesic, would worsen the respiratory depression. Acetaminophen would not reverse opioid-induced respiratory depression. Nalbuphine, while it is an opioid antagonist, it also has agonist properties and is not the primary choice for reversing severe opioid-induced respiratory depression.