Methemoglobinemia — Management Pathway

Step-by-step decision

Choose step by step as prompted; reaching an endpoint gives the management recommendation. You can go back a step or restart anytime.

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Full pathway

1. [Decision] Antidote needed?
   Cyanosis + saturation gap — is an antidote needed? (Iron Fe2+ → Fe3+ cannot carry oxygen (oxidizers: benzocaine/prilocaine/lidocaine, nitrites, dapsone, nitroglycerin, etc.). Cyanosis not relieved by oxygen + chocolate-brown blood + a saturation gap (pulse oximetry ~85% while ABG PaO2 is normal/high, gap >5%). Pulse oximetry is unreliable — confirm with blood-gas co-oximetry (sulfhemoglobin is misread as methemoglobin). Severity by absolute amount (Hb × %MetHb).)
   • Symptomatic / MetHb >20–30% → Symptomatic → methylene blue
   • Mild, asymptomatic → Mild, asymptomatic · stop drug, support
2. [End] Mild, asymptomatic · stop drug, support
   Mild, asymptomatic (low MetHb): stop the offending oxidizer, oxygen, support, monitor; most recover spontaneously once the drug is stopped. Escalate to antidote if symptoms appear or MetHb rises.
3. [End] Symptomatic → methylene blue
   Symptomatic or MetHb >20–30%: methylene blue 1–2 mg/kg IV push (over >5 min, may repeat). Contraindicated/use with caution: G6PD deficiency (causes hemolysis and is ineffective — use high-dose vitamin C/exchange transfusion/hyperbaric oxygen instead), concurrent serotonergic drugs (methylene blue is an MAOI → serotonin syndrome), pregnancy; high doses (>5–7 mg/kg) paradoxically cause methemoglobinemia/hemolysis. Refractory: exchange transfusion, hyperbaric oxygen. Stop the oxidizer, oxygen, support.

Source guidelines & references

• Methemoglobinemia (StatPearls; WikEM)

This pathway is our own synthesis of the decision logic in the guidelines above (not the guideline verbatim); thresholds and workflows change as guidelines update — in practice follow the latest guideline, your institution's protocol and the individual patient.

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