Methemoglobinemia

• Autor(a) principal: Murinello, António
• Data de Publicação: 2023
• Outros Autores: Bicho, Manuel, Estrela Inácio, Rosa, Loureiro, Maria Conceição
• Tipo de documento: Artigo
• Idioma: por
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: https://revista.spmi.pt/index.php/rpmi/article/view/2023
• topic: Meta-hemoglobinemia; azul de metileno; redutase do citocrómio-b; Methemoglobinemia; methylene blue; cytochrome-b

Methemoglobinemia refers to the existence of high blood concentrations of methemoglobin, resulting from the oxidation offerrous iron to ferric iron within the hemoglobin molecule. An extensive review of methemoglobinemia is done, initiaJJy focusing on physiological enzymatic mechanisms of oxidation/ reduction of hemoglobin, referring its efficacy in pathologic methemoglobinemia. Methe­ moglobinemia causes tissue hypoxia, being responsible for chocolate colour type of cyanosis, and other progressive symptoms, including abnormalities of respiratory and cardiac function as the concentration of methemoglobin grow up. Etiology can be genetic or acquired. Acquired form is much more common, and there are a great number of oxidizing agents causing it, namely dn,gs. The most common genetic cause is deficiency of enzymatic system of cytochrome-b5 reductase, from which we know three differentgenetic variations with weak activity. Laboratory confirmation of methemoglobinemia requires co-oxymetry, but clinicai diagnosis is essential. Oxidizing  agents  besides  causing  methe­ moglobinemia can be responsible for some degree of hemolysis, mostly if there is concomitant deficiency of glucose-6-phosphate dehydrogenase, in which case it is better not to use methylene blue in the treatment of methemoglobinemia. ln high doses methylene blue is an oxidizing agent, causing induction of methemoglobin. If there is deficiency of the referred enzyme, the haemolytic action of methylene blue will happen with lower doses of the drug. Exchange transfusions are alternative therapy in serious cases. Recently N-acetylcysteine is being considered as alternative therapy to methylene blue.