RT Book, Section A1 Bissonnette, Bruno A1 Luginbuehl, Igor A1 Engelhardt, Thomas SR Print(0) ID 1164078566 T1 Methemoglobinemia (Congenital) T2 Syndromes: Rapid Recognition and Perioperative Implications, 2e YR 2019 FD 2019 PB McGraw-Hill Education PP New York, NY SN 9781259861789 LK accessanesthesiology.mhmedical.com/content.aspx?aid=1164078566 RD 2024/03/28 AB Congenital presence of high levels of methemoglobin in blood. The presence of abnormally high levels of methemoglobin in the blood is the result of a congenital anomaly of one chain of hemoglobin (hemoglobins M) or congenital deficit in NADH cytochrome b5 reductase. Clinically, patients with a blood level around 15% present shortness of breath, cyanosis, mental status changes in 50% of patients, headache, fatigue, exercise intolerance, dizziness, and loss of hairlines. Patients with severe methemoglobinemia (>50%) have seizures, coma, and death (>70%). Healthy people may not have many symptoms with methemoglobin levels below 15%. However, patients with comorbidities, such as anemia, cardiovascular disease, lung disease, sepsis, or presence of other abnormal hemoglobin species (eg, carboxyhemoglobin, sulfhemoglobin, or sickle hemoglobin), may experience moderate-to-severe symptoms with levels as low as 5 to 8%.