**Core Concept**
In labour wards, patients often receive opioid analgesia to manage pain. However, opioids can cause respiratory depression, a life-threatening condition that requires immediate reversal. Naloxone is a specific antidote designed to counteract opioid effects, making it a critical component in labour ward emergency kits.

**Why the Correct Answer is Right**
Naloxone works by competitively binding to opioid receptors in the brain and peripheral tissues, thereby reversing the effects of opioids. This includes the reversal of analgesia, sedation, and respiratory depression. Naloxone's rapid onset of action allows for prompt intervention in cases of opioid-induced respiratory failure. The recommended dose of naloxone is 0.2-0.4 mg IV, with repeated doses as needed to maintain adequate respiration.

**Why Each Wrong Option is Incorrect**
**Option A:** Fentanyl is an opioid analgesic itself and would not be used to reverse opioid-induced respiratory depression.
**Option C:** Morphine is another opioid analgesic that would exacerbate respiratory depression, not reverse it.
**Option D:** Bupivacaine is a local anaesthetic used for regional analgesia in labour and would not be effective in reversing opioid-induced respiratory depression.

**Clinical Pearl / High-Yield Fact**
Always remember the mnemonic "NARCAN" to recall the antidote for opioid-induced respiratory depression: Naloxone And Resuscitation, Cardiac Arrest, and Neurological assessment. This mnemonic helps you recall the importance of naloxone in emergency situations.

**✓ Correct Answer: B. Naloxone**