Methemoglobinemia: Difference between revisions
No edit summary |
|||
(12 intermediate revisions by 5 users not shown) | |||
Line 3: | Line 3: | ||
*Methemoglobin refers to ferric form of hemoglobin (Fe3+) that is unable to bind O2 | *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 | *Suspect in any patient with cyanosis not responsive to supplemental O2 | ||
**Consider in pediatric patient (<6 months) with diarrhe and low oxygen saturation | |||
===Causes | ===Causes=== | ||
*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<ref>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.</ref><ref>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.</ref> | ||
**[[Benzocaine]] and other local anesthetics | **[[Benzocaine]] and other local anesthetics | ||
**[[Cyanokit]], nitrites, nitrates, well water (nitrates) | **[[Cyanokit]], nitrites, nitrates, well water (nitrates) | ||
Line 18: | Line 19: | ||
[[File:Eplasty16ic18 fig1.jpg|thumb|Cyanosis from methemoglobinemia.]] | [[File:Eplasty16ic18 fig1.jpg|thumb|Cyanosis from methemoglobinemia.]] | ||
[[File:Eplasty16ic18 fig3.jpg|thumb|Cyanosis resolved after methylene blue.]] | [[File:Eplasty16ic18 fig3.jpg|thumb|Cyanosis resolved after methylene blue.]] | ||
[[File:PMC4987464 CRIEM2016-9013816.001.png|thumb|Severe methemoglobinemia.]] | |||
[[File:ChocolateBrownBlood (cropped)2.jpg|thumb|Chocolate-brown blood due to methemoglobinemia.]] | [[File:ChocolateBrownBlood (cropped)2.jpg|thumb|Chocolate-brown blood due to methemoglobinemia.]] | ||
{| {{table}} | |||
| align="center" style="background:#f0f0f0;"|'''MetHb level (%)''' | |||
| align="center" style="background:#f0f0f0;"|'''Signs & Symptoms^''' | |||
|- | |||
| <3||None | |||
|- | |||
| 3-15||Blue/slate-gray skin | |||
|- | |||
| 15-30||Cyanosis, chocolate-brown blood | |||
|- | |||
| 30-50||[[Breathlessness]], [[headache]], [[dizziness]], [[syncope]] | |||
|- | |||
| 50-70||Tachypnea, [[myocardial ischemia]], [[lactic acidosis]], [[arrythmia]], [[seizure]], [[CNS depression]], [[coma]] | |||
|- | |||
| >70||Death | |||
|} | |||
^''Patients with [[anemia]] or preexisting cardiopulmonary disease will show symptoms sooner'' | |||
*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> | ||
Line 39: | Line 53: | ||
[[File:ChocolateBrownBlood (cropped).jpg|thumb|Chocolate-brown blood due to methemoglobinemia.]] | [[File:ChocolateBrownBlood (cropped).jpg|thumb|Chocolate-brown blood due to methemoglobinemia.]] | ||
[[File:MethemoglobinDiag.jpg|thumb|Color chart for the detection of the amount of methemoglobin in the blood.]] | [[File:MethemoglobinDiag.jpg|thumb|Color chart for the detection of the amount of methemoglobin in the blood.]] | ||
*Diagnosis requires high index of suspicion; lack of improvement in oxygen saturation with high-flow oxygen plus discrepancy in oxygen saturation >5% between measurements by ABG vs pulse oximetry ("saturation gap") should raise suspicion. Diagnosis is then confirmed by measuring level of methemoglobin in blood | |||
*Co-oximetry | *Co-oximetry | ||
**Measures relative levels of oxyhemoglobin, carboxyhemoglobin, methemoglobin, reduced hemoglobin | **Measures relative levels of oxyhemoglobin, carboxyhemoglobin, methemoglobin, reduced hemoglobin | ||
Line 49: | Line 64: | ||
==Management== | ==Management== | ||
*[[High-Flow Oxygen]] | |||
** All patients warrant supplemental oxygen. Symptoms may improve with a non-rebreather but the pulse oximeter reading will remain unchanged and patients may remain cyanotic. This is a diagnostic clue. | |||
*[[Methylene blue]] | *[[Methylene blue]] | ||
**Treat if symptomatic '''OR''' asymptomatic with MetHb >25% | **Treat if symptomatic '''OR''' asymptomatic with MetHb >25% | ||
Line 62: | Line 80: | ||
==Disposition== | ==Disposition== | ||
*Will vary depending on response to the antidote and persistence of symptoms. Discuss with toxicologist/[[poison control]] | |||
==See Also== | ==See Also== | ||
*[[Toxicology (Main)]] | |||
*[[Toxidromes]] | *[[Toxidromes]] | ||
*[[Dyshemoglobinemia]] | *[[Dyshemoglobinemia]] | ||
*[[Carbon monoxide]] | |||
*[[Cyanide toxicity]] | |||
==External Links== | |||
*http://www.emdocs.net/tox-card-methemoglobinemia/ | |||
==References== | ==References== |
Latest revision as of 18:46, 15 March 2023
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
- Consider in pediatric patient (<6 months) with diarrhe and low oxygen saturation
Causes
- Rarely congenital, NADH reductase deficiency - unable to reduce ferric to ferrous iron (Fe3+ → Fe2+)
- Exposure to oxidizing agent[1][2]
- 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
MetHb level (%) | Signs & Symptoms^ |
<3 | None |
3-15 | Blue/slate-gray skin |
15-30 | Cyanosis, chocolate-brown blood |
30-50 | Breathlessness, headache, dizziness, syncope |
50-70 | Tachypnea, myocardial ischemia, lactic acidosis, arrythmia, seizure, CNS depression, coma |
>70 | Death |
^Patients with anemia or preexisting cardiopulmonary disease will show symptoms sooner
- Ask about family or personal history of G6PD deficiency as methylene blue contraindicated[4]
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
- Pulmonary
- Airway obstruction
- Anaphylaxis
- Angioedema
- Aspiration
- Asthma
- Cor pulmonale
- Inhalation exposure
- Noncardiogenic pulmonary edema
- Pneumonia
- Pneumocystis Pneumonia (PCP)
- Pulmonary embolism
- Pulmonary hypertension
- Tension pneumothorax
- Idiopathic pulmonary fibrosis acute exacerbation
- Cystic fibrosis exacerbation
- Cardiac
- Other Associated with Normal/↑ Respiratory Effort
- Other Associated with ↓ Respiratory Effort
Non-Emergent
- ALS
- Ascites
- Uncorrected ASD
- Congenital heart disease
- COPD exacerbation
- Fever
- Hyperventilation
- Interstitial lung disease
- Neoplasm
- Obesity
- Panic attack
- Pleural effusion
- Polymyositis
- Porphyria
- Pregnancy
- Rib fracture
- Spontaneous pneumothorax
- Thyroid Disease
- URI
Evaluation
- Diagnosis requires high index of suspicion; lack of improvement in oxygen saturation with high-flow oxygen plus discrepancy in oxygen saturation >5% between measurements by ABG vs pulse oximetry ("saturation gap") should raise suspicion. Diagnosis is then confirmed by measuring level of methemoglobin in blood
- 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
- High-Flow Oxygen
- All patients warrant supplemental oxygen. Symptoms may improve with a non-rebreather but the pulse oximeter reading will remain unchanged and patients may remain cyanotic. This is a diagnostic clue.
- 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
- Will vary depending on response to the antidote and persistence of symptoms. Discuss with toxicologist/poison control
See Also
External Links
References
- ↑ 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.
- ↑ 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.
- ↑ 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.
- ↑ Denshaw-Burke et al. Methemoglobinemia: Practice Essentials. Jan 4, 2016. http://emedicine.medscape.com/article/204178-overview
- ↑ Denshaw-Burke et al. Methemoglobinemia: Practice Essentials. Jan 4, 2016. http://emedicine.medscape.com/article/204178-overview