Correct Answer: Opioid overdose (opioid-induced respiratory depression)

Explanation

This presentation is highly characteristic of severe opioid toxicity. The combination of:

• Marked central nervous system depression → drowsiness progressing to unresponsiveness
• Severe respiratory depression → respiratory rate 7/min
• Hypoxemia → SpO₂ 84%
• Pinpoint pupils (miosis)
• Sudden deterioration after an unknown substance exposure

strongly suggests an opioid overdose.

The classic clinical triad of opioid overdose is:

Depressed consciousness + respiratory depression + pinpoint pupils

The WHO specifically describes opioid overdose by the combination of unconsciousness, low respiratory rate, and pinpoint pupils.

Opioids such as heroin, morphine, fentanyl, codeine, methadone, buprenorphine, and tramadol can produce this toxidrome. Opioids suppress the respiratory centers in the brainstem, reducing the normal ventilatory response to carbon dioxide. Severe toxicity can therefore progress from hypoventilation and hypoxemia to respiratory arrest and death.

Why are the pupils pinpoint?

Miosis is a characteristic effect of opioid receptor activation. Although pinpoint pupils are not absolutely required for diagnosis, their presence together with profound respiratory depression and reduced consciousness is highly suggestive of opioid poisoning. The CDC lists unresponsiveness, slow or shallow breathing, and small constricted pupils among the major signs of opioid overdose.

Immediate management

This patient has life-threatening respiratory depression, so management should begin with airway and breathing support, rather than waiting for toxicology results.

Initial priorities:

1. Airway assessment and positioning
2. Provide supplemental oxygen
3. Assist ventilation with bag-mask ventilation if breathing is inadequate
4. Administer naloxone when opioid overdose is suspected
5. Continue monitoring respiratory rate, oxygenation, consciousness, and recurrence of respiratory depression.

Naloxone is a competitive opioid receptor antagonist that rapidly reverses opioid-induced respiratory depression. WHO guidance emphasizes that in suspected opioid overdose, first responders should prioritize airway management, assisted ventilation, and naloxone.

Naloxone should be titrated to restoration of adequate spontaneous ventilation, rather than simply aiming for complete awakening. Repeated doses may be required because some opioids have a longer duration of action than naloxone.

Clinical Pearl

In an unconscious adolescent with an unknown substance exposure, severe respiratory depression plus pinpoint pupils should be treated as suspected opioid overdose, even when the specific opioid is unknown. Naloxone has little effect in patients who have not taken opioids, so it can be administered when opioid overdose is strongly suspected while definitive assessment continues

A useful exam mnemonic is:

“Down, slow, and small”

• Down → depressed consciousness
• Slow → slow breathing
• Small → small pupils

You can also practice another MCQ on Poisoning. 

External Resources

For further reading on recognition and emergency management of opioid overdose:

• World Health Organization (WHO): Opioid Overdose — Provides information on the clinical features of opioid overdose, including respiratory depression, unconsciousness, and pinpoint pupils, as well as the role of naloxone.
• Centers for Disease Control and Prevention (CDC): 5 Things to Know About Naloxone — Provides practical information on recognizing opioid overdose and the use of naloxone.

References

1. World Health Organization. Opioid overdose. WHO; 2025.
2. World Health Organization. Community management of opioid overdose. Geneva: World Health Organization; 2014.
3. Centers for Disease Control and Prevention. 5 Things to Know About Naloxone. CDC; 2024.