From the Guidelines
Methemoglobinemia symptoms include bluish discoloration of the skin, shortness of breath, fatigue, headache, dizziness, and confusion, with severity correlating with methemoglobin levels, and treatment typically involving removal of the offending agent and administration of methylene blue for symptomatic patients or those with levels above 20%. The symptoms of methemoglobinemia occur due to the inability of methemoglobin to carry oxygen effectively, resulting in tissue hypoxia 1. Methemoglobinemia can be congenital or acquired through exposure to certain medications or chemicals like nitrates, local anesthetics, dapsone, and some antibiotics 1.
Key Symptoms
- Bluish discoloration of the skin (cyanosis)
- Shortness of breath
- Fatigue
- Headache
- Dizziness
- Confusion
- Seizures, arrhythmias, and coma or death in severe cases
Treatment
- Removal of the offending agent
- Administration of methylene blue (1-2 mg/kg IV over 5 minutes) for symptomatic patients or those with levels above 20% 1
- Alternative treatment with ascorbic acid or hyperbaric oxygen therapy in severe cases or for patients with G6PD deficiency
- Supportive therapy, including intravenous hydration, oxygen supplementation, and cardiopulmonary support as needed 1
Severity and Treatment
The severity of symptoms correlates with methemoglobin levels, with mild symptoms appearing at 10-20% levels, moderate symptoms at 20-50%, and severe, life-threatening symptoms above 50% 1. Treatment should be initiated for symptomatic patients or those with high methemoglobin levels, with methylene blue being the first-line treatment 1.
From the Research
Methemoglobinemia Symptoms
- Methemoglobinemia presents clinically with symptoms and signs of tissue hypoxia, including headache, dizziness, nausea, and cyanosis 2, 3
- Concentrations around 80% are life-threatening 2
- Features of toxicity may develop over hours or even days when exposure, whether by inhalation or repeated skin contact, is to relatively low concentrations of inducing chemical(s) 2
- The 'cyanosis' is unresponsive to oxygen therapy 2
- Shortness of breath and respiratory distress are also common symptoms 3
Diagnosis and Treatment
- Pulse oximetry is unreliable in the presence of methemoglobinemia 2
- Arterial blood gas analysis is mandatory in severe poisoning and reveals normal partial pressures of oxygen (pO2) and carbon dioxide (pCO2,) a normal 'calculated' haemoglobin oxygen saturation, an increased methaemoglobin concentration and possibly a metabolic acidosis 2
- Methylene blue can be used successfully provided the patient has no evidence of glucose 6 phosphate deficiency 4, 5, 6
- Hyperbaric oxygen and intravenous ascorbic acid are other treatment options 4, 5, 6
- Plasmapheresis may have a role in severe methemoglobinemia unresponsive to standard treatment options 4