Critically Ill Patient with Acquired Refractory Methemoglobinemia Successfully Treated with Therapeutic Erythrocytapheresis: A Case Report

REPORTalkalosis, pO 2 -369 mm Hg, and methemoglobin was 15%.The oxygen saturation gap, that is, the difference between oxygen saturation in arterial blood gas sample (SaO 2 ) and SpO 2, was greater than 5%.His blood was chocolate brown in color.The patient had methemoglobinemia, probably due to poisoning.In the meantime, the patient had seizures and was intubated.Around 60 mg (1 mg/kg) of intravenous (IV) methylene blue was administered over 3 hours, and the patient was shifted to the ICU.The patient was continued on mechanical ventilator support.SpO 2 remained 85% on 100% FiO 2 .The patient was drowsy without any sedation.Hemodynamics were stable.G6PD levels and other lab investigations were normal.The ABG taken on the next day at 7:30 am showed 3.9% methemoglobin.As cyanosis persisted, a second dose of 60 mg IV methylene blue was given.Despite two doses of methylene blue, SpO 2 remained 85% on 100% FiO 2 .The 1,