Methemoglobinemia
An oxygen saturation in the 80s should not generally cause cyanosis (usually it must be substantially lower before cyanosis occurs). Thus, any time a patient has cyanosis with an oxygen saturation in the 80s, this suggests methemoglobinemia - Josh Farkas
image by: Anesthesia
HWN Recommends
EM@3AM: Methemoglobinemia
Normally we have ~1-3% methemoglobin in our blood and physiologic mechanisms to convert methemoglobin back to hemoglobin. When these mechanisms are overwhelmed, clinically apparent methemoglobin develops...
Infants <3 months old are more susceptible to methemoglobinemia due to fetal hemoglobin being more easily oxidized and children having ~60% activity of cytochrome b5 reductase. Well-water with high levels of nitrates poses a high risk of methemoglobinemia in kids, called “blue baby syndrome.” Enteritis-associated methemoglobinemia can be present in over 60% of infants with severe diarrhea.
Resources
A Real Pain in the Mouth: Acquired Methemoglobinemia
For patients presenting with hypoxia and cyanosis, acquired methemoglobinemia should be included on the differential. Dapsone and topical anesthetics are common offenders in methemoglobinemia, so a thorough medication history is pertinent to diagnosing and treating this condition.
Methemoglobinemia
Methylene Blue - Give 1-2 mg/kg IV over 5 minutes. Clinical improvement should occur within minutes. However, methylene blue may cause transient drops in the measured oxygen saturation (due to its blue pigment). Cyanosis should resolve within an hour.
A Rare Culprit of Methemoglobinemia
While methemoglobinemia may be inherited, its acquired form occurs when hemoglobin is exposed to oxidizing agents and is far more prevalent. Nitrate-containing compounds have been classically described as causing methemoglobinemia, ranging from aniline dyes and pesticides to medications, such as nitroglycerin, nitroprussides, and silver nitrite.1,2 Other commonly used drugs include sulfonamides, dapsone, and benzocaine—the latter 2 accounting for up to 45% of all drug-induced methemoglobinemia cases.
Acquired methemoglobinemia in infants
Methemoglobinemia is an uncommon cause of cyanosis. It should be suspected in an infant with cyanosis who has no respiratory distress or cyanotic congenital heart disease.
Blue babies and nitrate-contaminated well water
The use of nitrate-contaminated drinking water to prepare infant formula is a well-known risk factor for infant methemoglobinemia. Affected infants develop a peculiar blue-gray skin color and may become irritable or lethargic, depending on the severity of their condition.
Code Blue: Life-threatening Methemoglobinemia
Methemoglobinemia should be suspected in all patients with sudden onset of cyanosis that does not improve with the administration of oxygen. Prompt administration of methylene blue should be the first-line treatment. Ascorbic acid can be used as adjuvant therapy when there is a contraindication to methylene blue, or when methylene blue is not available.
Homemade Baby Food: The Danger of Nitrates
Nitrates aren’t the only cause of methemoglobinemia. Certain antibiotics and the numbing agent found in teething gels can also convert hemoglobin to methemoglobin. And baby food isn’t the only dietary source of nitrates. Drinking water (especially well water) can contain high levels of nitrates from fertilizer run-off. In fact, the most common cause of methemoglobinemia in babies (including those older than 6 months of age) is the ingestion of infant formula made with nitrate-containing well water!
How to recognize and treat acquired methemoglobinemia
Pulse oximetry is inaccurate in the presence of significant methemoglobinemia and cannot be relied on.
Infant Methemoglobinemia (Blue Baby Syndrome)
Methemoglobinemia is a condition that some babies are born with (congenital) or some develop early in life (acquired). Acquired methemoglobinemia is more common than the congenital form. It can be caused by exposure to a variety of substances and by some health conditions.
Methemoglobinemia and Other Dyshemoglobinemias
Methemoglobin is a metalloprotein, in which the iron in the heme group is in the Fe3+(ferric), not the Fe2+(ferrous), state of normal hemoglobin (Hb). Methemoglobinemia occurs because of either increased production of oxidized Hb due to exposure to environmental agents or diminished reduction of oxidized Hb because of underlying germline mutations.
Methemoglobinemia: Cyanosis and Street Methamphetamines
Methemoglobinemia can be detected with a simple office test. After placing 1 drop of the patient's blood on a piece of filter paper next to a drop of blood from a normal individual, when dry, the methemoglobin-containing blood will turn a deep chocolate-brown or slate-gray color.
REBEL Core Cast 90.0 – Methemoglobinemia
Methemoglobinemia can result from exposure to a number of different medications. The most common are dapsone and topical anesthetic agents (i.e. benzocaine) Consider the diagnosis in any patient with cyanosis and hypoxia that doesn’t respond to oxygen administration. Administer methylene blue to any patient with abnormal vital signs, metabolic acidosis, end organ dysfunction or, a serum level > 25%.
Recommendations for diagnosis and treatment of methemoglobinemia
Acquired methemoglobinemia is the consequence of drug ingestion or toxic exposure that cause acceleration of Hb oxidization from the ferrous to the ferric state.. The drugs that cause methemoglobinemia are numerous, including sulfonamides, lidocaine and other aniline derivatives, and nitrites. The most common drugs are benzocaine and lidocaine. Nitrates and the nitrites contaminating water supplies or used as preservatives in foods can also be trigger agents.
The Blue Baby Syndromes
Did environment or infection cause a blood disorder in newborns?
EM@3AM: Methemoglobinemia
VBG or ABG (both give same result for methemoglobin level) in a fresh sample of blood. Methemoglobin levels increase with prolonged storage. With some POC ABGs you will need to specifically order a methemoglobin level; this is laboratory dependent.
StatPearls
Methemoglobinemia is a condition with life-threatening potential in which diminution of the oxygen-carrying capacity of circulating hemoglobin occurs due to the conversion of some or all of the four iron species from the reduced ferrous (Fe2+) state to the oxidized ferric (Fe3+) state. Ferric iron is unable to bind and transport oxygen. Increased levels of methemoglobin results in functional anemia.
Introducing Stitches!
Your Path to Meaningful Connections in the World of Health and Medicine
Connect, Collaborate, and Engage!
Coming Soon - Stitches, the innovative chat app from the creators of HWN. Join meaningful conversations on health and medical topics. Share text, images, and videos seamlessly. Connect directly within HWN's topic pages and articles.