Methemoglobinemia: Difference between revisions
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*Rarely congenital, NADH reductase deficiency - unable to reduce ferric to ferrous iron (Fe<sup>3+</sup> → Fe<sup>2+</sup>)
*Rarely congenital, NADH reductase deficiency - unable to reduce ferric to ferrous iron (Fe<sup>3+</sup> → Fe<sup>2+</sup>)
*Exposure to oxidizing agent
*Exposure to oxidizing agent
**Benzocaine and other local anesthetics
**[[Benzocaine]] and other local anesthetics
**cyanide kit, nitrites, nitrates, well water (nitrates)
**[[Cyanokit]], nitrites, nitrates, well water (nitrates)
**Antimalarials
**[[Antimalarials]]
**Quinolones
**[[Quinolones]]
**Dapsone (used to treat leprosy, PCP pneumonia, toxoplasmosis, dermatitis herpetiformis, brown recluse bite)
**[[Dapsone]] (used to treat leprosy, PCP pneumonia, toxoplasmosis, dermatitis herpetiformis, brown recluse bite)
**Aniline dyes
**Aniline dyes
**Phenazopyridine<ref>Jeffery WH, Zelicoff AP, Hardy WR. Acquired methemoglobinemia and hemolytic anemia after usual doses of phenazopyridine. Drug Intell Clin Pharm. 1982 Feb;16(2):157-9.</ref>
**Phenazopyridine<ref>Jeffery WH, Zelicoff AP, Hardy WR. Acquired methemoglobinemia and hemolytic anemia after usual doses of phenazopyridine. Drug Intell Clin Pharm. 1982 Feb;16(2):157-9.</ref>
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==Clinical Features==
==Clinical Features==
*Depends on level of metHb
*Depends on level of metHb
**''Patients with anemia or preexisting cardiopulmonary disease will show symptoms sooner''
**''Patients with [[anemia]] or preexisting cardiopulmonary disease will show symptoms sooner''
**<20%: asymptomatic, gray-blue cyanosis
**<20%: asymptomatic, gray-blue cyanosis
**20-30%: anxiety, headache, weakness, light-headedness, tachycardia
**20-30%: anxiety, [[headache]], [[weakness]], light-headedness, [[tachycardia]]
**50-60%: myocardial ischemia, dysrhythmias, depressed mental status, seizure
**50-60%: [[myocardial ischemia]], [[dysrhythmias]], depressed mental status, [[seizure]]
**>70%: usually fatal
**>70%: usually fatal
*Ask about family or personal history of G6PD deficiency as methylene blue contraindicated<ref>Denshaw-Burke et al. Methemoglobinemia: Practice Essentials. Jan 4, 2016. http://emedicine.medscape.com/article/204178-overview</ref>
*Ask about family or personal history of G6PD deficiency as methylene blue contraindicated<ref>Denshaw-Burke et al. Methemoglobinemia: Practice Essentials. Jan 4, 2016. http://emedicine.medscape.com/article/204178-overview</ref>
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==Differential Diagnosis==
==Differential Diagnosis==
*Consider rare entity of [[sulfhemoglobinemia]]
*Consider rare entity of [[sulfhemoglobinemia]]
**Sulfonamides, sulfasalazine, phenazopyridine
**[[Sulfonamides]], [[sulfasalazine]], [[phenazopyridine]]
**Occupational exposure
**Occupational exposure
**Conventional co-oximerty misidentifies sulfhemoglobin as methemoglobin so diagnosis is suspected when patient does not respond to methylene blue
**Conventional co-oximerty misidentifies sulfhemoglobin as methemoglobin so diagnosis is suspected when patient does not respond to methylene blue
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*[[Methylene blue]]
*[[Methylene blue]]
**Treat if symptomatic '''OR''' asymptomatic with MetHb >25%
**Treat if symptomatic '''OR''' asymptomatic with MetHb >25%
**1-2mg/kg Methylene Blue IV over 5min; repeat dose if no effect
**1-2mg/kg [[Methylene blue]] IV over 5min; repeat dose if no effect
**Improvement seen within 20min
**Improvement seen within 20min
**'''Contraindicated in [[G6PD]] deficiency'''
**'''Contraindicated in [[G6PD]] deficiency'''
***May induce acute hemolytic anemia
***May induce acute [[hemolytic anemia]]
***Instead use moderate dose of ascorbic acid (vitamin C),  300 to 1000 mg/day orally in divided doses
***Instead use moderate dose of ascorbic acid (vitamin C),  300 to 1000 mg/day orally in divided doses
*Other treatment modalities<ref>Denshaw-Burke et al. Methemoglobinemia: Practice Essentials. Jan 4, 2016. http://emedicine.medscape.com/article/204178-overview</ref>
*Other treatment modalities<ref>Denshaw-Burke et al. Methemoglobinemia: Practice Essentials. Jan 4, 2016. http://emedicine.medscape.com/article/204178-overview</ref>
**[[Exchange transfusion]] for symptomatic methemoglobinemia in patient with G6PD deficiency
**[[Exchange transfusion]] for symptomatic methemoglobinemia in patient with G6PD deficiency
**Hyperbaric O2 when methylene blue ineffective or contraindicated
**Hyperbaric O2 when methylene blue ineffective or contraindicated
**IV hydration and bicarbonate for metabolic acidosis
**IV hydration and [[bicarbonate]] for metabolic acidosis


==Disposition==
==Disposition==

Revision as of 22:05, 20 August 2019

Background

  • Methemoglobin refers to ferric form of hemoglobin (Fe3+) that is unable to bind O2
  • Suspect in any patient with cyanosis not responsive to supplemental O2

Causes[1][2]

  • Rarely congenital, NADH reductase deficiency - unable to reduce ferric to ferrous iron (Fe3+ → Fe2+)
  • Exposure to oxidizing agent
    • Benzocaine and other local anesthetics
    • Cyanokit, nitrites, nitrates, well water (nitrates)
    • Antimalarials
    • Quinolones
    • Dapsone (used to treat leprosy, PCP pneumonia, toxoplasmosis, dermatitis herpetiformis, brown recluse bite)
    • Aniline dyes
    • Phenazopyridine[3]

Clinical Features

  • Depends on level of metHb
  • Ask about family or personal history of G6PD deficiency as methylene blue contraindicated[4]
Methemoglobinemia.JPG

Differential Diagnosis

  • Consider rare entity of sulfhemoglobinemia
    • Sulfonamides, sulfasalazine, phenazopyridine
    • Occupational exposure
    • Conventional co-oximerty misidentifies sulfhemoglobin as methemoglobin so diagnosis is suspected when patient does not respond to methylene blue
    • Typically requires no treatment other than removal of offending agent
    • Blue-green discoloration of blood

Acute dyspnea

Emergent

Non-Emergent

Evaluation

  • Co-oximetry
    • Measures relative levels of oxyhemoglobin, carboxyhemoglobin, methemoglobin, reduced hemoglobin
    • Usually performed on arterial blood sample, but fingertip CO-oximeter devices are available
  • Normal PaO2
  • SpO2 will initially be falsely elevated
    • Once MetHb >30% → SpO2 will fall to 80-85%
    • Mid-80s SpO2 due to light absorption of both oxyHb and deoxyHb
  • "Chocolate brown" color of blood

Management

  • Methylene blue
    • Treat if symptomatic OR asymptomatic with MetHb >25%
    • 1-2mg/kg Methylene blue IV over 5min; repeat dose if no effect
    • Improvement seen within 20min
    • Contraindicated in G6PD deficiency
      • May induce acute hemolytic anemia
      • Instead use moderate dose of ascorbic acid (vitamin C), 300 to 1000 mg/day orally in divided doses
  • Other treatment modalities[5]
    • Exchange transfusion for symptomatic methemoglobinemia in patient with G6PD deficiency
    • Hyperbaric O2 when methylene blue ineffective or contraindicated
    • IV hydration and bicarbonate for metabolic acidosis

Disposition

See Also

References

  1. ↑ Fernandez-Frackelton M, Bocock J: Cyanosis, in Marx JA, Hockberger RS, Walls RM, et al (eds): Rosen’s Emergency Medicine: Concepts and Clinical Practice, ed 7. St. Louis, Mosby, Inc., 2010, (Ch) 29:p 211-216.
  2. ↑ Mody, A., Silverman, B.: Problems in the Early Neonatal Period, In Fleisher and Ludwig's Textbook of Pediatric Emergency Medicine, Lippincott, WIlliams and Wilkins 2010, Page 995.
  3. ↑ Jeffery WH, Zelicoff AP, Hardy WR. Acquired methemoglobinemia and hemolytic anemia after usual doses of phenazopyridine. Drug Intell Clin Pharm. 1982 Feb;16(2):157-9.
  4. ↑ Denshaw-Burke et al. Methemoglobinemia: Practice Essentials. Jan 4, 2016. http://emedicine.medscape.com/article/204178-overview
  5. ↑ Denshaw-Burke et al. Methemoglobinemia: Practice Essentials. Jan 4, 2016. http://emedicine.medscape.com/article/204178-overview
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