Question

"A 56-year-old man was found unconscious at home with a respiratory rate of 6 breaths per minute and pinprick pupils. An ambulance was called and the paramedics administered naloxone.

An arterial blood gas was performed on arrival to A&E, after the patient has just been started on 15L of oxygen. It revealed the following:
PaO2: 7.5 kPa (56 mmHg)
pH: 7.31
PaCO2: 7.1 kPa (53 mmHg)
HCO3-: 24 mmol/L
BE: +1
What does the ABG show?
(A) 7.5 kPa (56 mmHg)
(B) 7.1 kPa (53 mmHg)
(C) 24 mmol/L
(D) +1

Answer 1

The ABG shows that the patient has respiratory acidosis with a pH below the normal range, indicating an acidotic state with no significant metabolic compensation. The patient’s presentation and treatment with naloxone suggest an opioid overdose.

Step-by-step explanation:

The arterial blood gas (ABG) of a 56-year-old man with a respiratory rate of 6 breaths per minute and pinprick pupils reveals the following results: PaO2: 7.5 kPa (56 mmHg), pH: 7.31, PaCO2: 7.1 kPa (53 mmHg), and HCO3-: 24 mmol/L. According to the reference values, a normal pH ranges from 7.35 to 7.45, indicating that a pH of 7.31 is considered acidotic. The elevated PaCO2 suggests respiratory acidosis, which is consistent with the patient's decreased respiratory rate. The normal bicarbonate level (HCO3-: 24 mmol/L) suggests there is no significant metabolic compensation occurring. Intervention with naloxone, an opioid-overdose antidote, was likely given due to suspicion of opioid overdose, accounting for the patient's presentation prior to A&E admission.

Opioid overdose can lead to significantly diminished respiratory rates, which in turn elevates PaCO2, causing a respiratory acidosis. The administered naloxone works by displacing the opioids from the receptors, reversing the opioid effects and hopefully restoring normal respiratory function.