What’s the treatment for this male patient’s illness?
A 25-year-old male presents to the emergency department for evaluation of shortness of breath. The patient reportedly used amyl nitrite “poppers” at a nightclub shortly before the onset of his symptoms. He is noted to be cyanotic. His heart rate is 120 and his respiratory rate is 18 with a room air oxygen saturation of 85%. Which of the following is the definitive treatment for the patient’s illness?
Question Answer Choices
- Endotracheal intubation
- Hydroxocobalamin
- Hyperbaric chamber
- Methylene blue
- Non-rebreather 15L O2
Question Explanation
Correct answer: D. Methylene blue
“Poppers” are a club drug initially popular in the disco era, but are now popular at raves. They are alkyl nitrite–class drugs. In this vignette, it is amyl nitrite. They cause a high and relax smooth muscles, the latter of which sometimes makes this a drug of choice for sexual benefit.
Sexual assault should be on the differential when encountering patients who are exposed to poppers. The drug can also cause methemoglobinemia, like the patient in this vignette.
Normally, hemoglobin alternates between a reduced and an oxidized form. The majority of the hemoglobin is in the Fe2+ state, with a small amount occurring in the Fe3+ state. The methemoglobin (Fe3+) is normally reduced by the enzyme cytochrome b5 reductase.
However, when oxidant stress occurs and the ability to reduce the Fe3+ to the Fe2+ is overwhelmed, the patient may exhibit signs of methemoglobinemia. Although this condition can be congenital, most cases are acquired. Commonly encountered etiologies include phenazopyridine, dapsone, local anesthetics and nitrites. Methemoglobinemia is treated with methylene blue. Methylene blue pulls an electron from the hexose monophosphate shunt (via the enzyme NADPH methemoglobin reductase) to help return the Fe3+ to the Fe2+.
Incorrect answer choices:
Pulse oximetry will falsely read 85-88% in the setting of methemoglobinemia. A pulse oximeter has a laser on one end and a laser detector at the other side. Deoxyhemoglobin bends the laser. The machine normally interprets the degree of deflection and is able to determine the percent deoxyhemoglobin.
In the case of methemoglobinemia, however, the deflection is such that the pulse oximeter assumes the saturation is around 85%. Thus, administration of additional oxygen via non-rebreather (Choice E) does not change the pulse oximeter. Similarly, endotracheal intubation is not indicated because the pulse oximetry fails to improve (Choice A).
Hyperbarics (Choice C) should not be used routinely in the treatment of methemoglobinemia. If methylene blue is not an option (e.g., contraindicated due to severe G6PD deficiency), one can consider hyperbarics as a bridging measure for critically-ill patients while preparing for exchange transfusion. However, most cases of methylene blue warrant treatment only with intravenous methylene blue.
Hydroxocobalamin (Choice B) is a metalloprotein with a central cobalt that binds cyanide, thereby forming cyanocobalamin, which is renally eliminated. It is used for cyanide toxicity, not methemoglobinemia.
References
Gresham C, LoVecchio F. Industrial toxins. Chapter 204. In: Tintinalli’s Emergency Medicine: A comprehensive study guide. Tintinalli JE (Eds). 9th Edition. McGraw Hill. New York. 2020.
