cyanosis, hypoxia, diagnostics


A 44-year-old lady offered with shortness of breath, fatigue, and bilateral decrease extremity edema. She was hypoxic to 85% on room air with pale pores and skin, cyanotic lips, and anasarca.

The affected person was persistently hypoxic to 85% regardless of being positioned on a nonrebreather at 15 L. She had just lately been admitted to a different hospital for renal failure, quantity overload, and coronary heart failure. She was identified with IgA nephropathy throughout that admission and began on high-dose steroids and diuretics.

She had gone to her clinic for her first rituximab infusion earlier than coming to our ED, however she was shortly transferred to the ED for quantity overload, initiation of upper dose diuretics, and concern for COVID-19. The affected person did have diffuse edema, however her lungs had been clear on examination, and her chest x-ray didn’t present pulmonary edema of diffuse, patchy opacities.

The affected person’s mom arrived with a bag of medicines from her current discharge that weren’t included within the affected person’s digital medical document. We discovered that she had been began on dapsone as prophylaxis for Pneumocystis jiroveci pneumonia.

What is that this affected person’s analysis?

Discover a dialogue on subsequent web page.

Prognosis: Methemoglobinemia (Not The whole lot is COVID)

We added a methemoglobin stage to the lab request as a result of she had been began on dapsone. It returned at 19.7%.

Methemoglobinemia is a congenital or acquired situation. Emergency physicians are most involved with the acquired model, which may be extreme and even deadly however is reversible. Acquired instances are mostly the results of elevated methemoglobin induced by drugs similar to anesthetics, antimalarial brokers, and aniline dyes; nitrates or nitrites; antifreeze; illicit medication that include nitrates or are lower with different inducing drugs; and, on this case, dapsone.

Methemoglobin is produced when a heme iron of hemoglobin is oxidized from the ferrous to the ferric state, which is unable to bind to oxygen. The inner enzyme cytochrome b5 reductase (Cyb5R) converts the ferric state to the ferrous state throughout regular metabolism of crimson blood cells, and it retains the physiologic stage of methemoglobin within the physique at any time to roughly 1%.

The stability of ferrous to ferric is disturbed and the extent of methemoglobin rises in a affected person who has a decrease quantity of Cyb5R or an awesome quantity of an inducing substance. The remaining ferrous iron within the hemoglobin tetrameric molecule will bind to oxygen with a better affinity in response to the ferric iron, and it’ll not launch wanted oxygen to the tissue. Given the decreased potential to dump and bind to out there oxygen, the affected person can undergo extreme tissue hypoxia even with oxygen administration.


Physicians might anchor on a COVID analysis when a affected person presents with hypoxia, however this case highlights the significance of sustaining a large differential utilizing bodily examination and chest radiograph to assist assist considerations, remembering that zebras do happen and recognizing anchor bias. Figuring out shortly that this affected person was not solely in danger for coronary heart failure and COVID but in addition for a extreme, deadly situation due to her drugs was key to treating her appropriately.

Her oxygen stage being persistently at 85% no matter intervention was one other clue. Pulse oximetry can not detect methemoglobin and causes an error in estimating the true oxygen stage, so it can show at roughly 85%. We drew arterial (determine on earlier web page) and venous blood gases (determine this web page contains ABG and VBG), and a visible inspection raised additional concern for methemoglobinemia as the reason for the affected person’s hypoxia. Blood in these sufferers is often described as trying like chocolate milk, and the ABG and VBG had been related in shade on this case, demonstrating a scarcity of oxygenation or oxygen offload.

Remedy for acquired methemoglobinemia is predicated on the methemoglobin stage and whether or not we now have concern for concomitant G6PD deficiency. A affected person with vital signs or a stage above 30% requires therapy with vitamin C or methylene blue, although a affected person with a historical past of G6PD deficiency ought to obtain vitamin C. The therapy of selection is methylene blue for many different instances. The preliminary therapy is the elimination of the offending agent and supportive take care of all instances.

Our affected person was began on methylene blue and stored within the hospital for 2 days for repeated doses due to the lengthy half-life of dapsone, which was discontinued. She was discharged dwelling on trimethoprim/sulfamethoxazole for PJP prophylaxis.

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Dr. Eutermoseris an assistant professor of emergency medication at Denver Well being and College of Colorado Hospital.

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