Authors: Dr. Sifrah Isaac , Dr. Nitin Jagasia

Abstract

Methemoglobinemia is a rare but life-threatening hematologic condition where hemoglobin is oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state, impairing oxygen delivery to tissues. While congenital forms exist, acquired methemoglobinemia often triggered by medications or chemical exposures is more common. Prevalence in pediatric populations is estimated at approximately 0.0015%. ​

Case Presentation: A 6-year-old male presented to the Apollo Hospitals Navi Mumbai Emergency Department with fever, abdominal pain, vomiting, epistaxis, and acute breathlessness. Physical examination revealed central and peripheral cyanosis with an SpO2 of 88% on room air, which only improved to 92% despite high-flow oxygen (10L). Notably, the patient had a history of exposure to a watch repair solution and prior consumption of "outside food." ​

Diagnostic Workup: Venous Blood Gas (VBG) analysis confirmed methemoglobinemia with a level (FMetHb) of 31.0% and respiratory alkalosis. Laboratory results showed mild thrombocytopenia (Platelets: 89,000) and a normal hemoglobin (15.5 g/dL). G6PD deficiency was ruled out. Despite initial chest X-ray findings suggesting cardiomegaly, 2D echocardiography with contrast confirmed normal cardiac function and no pulmonary arteriovenous malformations.

 ​Management and Outcome: The primary objective was to restore oxygen-carrying capacity. The patient received a 1 mg/kg IV bolus of Methylene Blue (20 mg diluted in 0.9% NS) over 15 minutes, alongside Vitamin C (500 mg BD) and supportive oxygen. Following the antidote, SpO2 improved to 100%, and cyanosis resolved. Post-treatment VBG showed FMetHb reduced to 6.1%. The patient remained hemodynamically stable and was successfully weaned from oxygen.

 ​Discussion: This case highlights the "saturation gap" low SpO2 unresponsive to supplemental oxygen as a clinical hallmark of methemoglobinemia. Prompt administration of Methylene Blue is the gold standard for levels >20% or symptomatic patients. ​

Conclusion: Early recognition of environmental toxins is critical for diagnosis. Management must focus on rapid reversal with Methylene Blue and comprehensive patient counseling to prevent re-exposure to oxidizing agents. In refractory cases, escalation to exchange transfusion or hyperbaric oxygen may be necessary. 

Keywords: Methhemoglobinemia