Methaemoglobinaemia

Abstract 

Methaemoglobin is formed when ferrous haemoglobin iron (II) is oxidized to ferric iron (III), which cannot participate in oxygen transport. Methaemoglobin-forming chemical groups of particular importance in poisoning are organic nitrites (e.g. amyl and isobutyl nitrite) and amino- or nitro-derivatives of benzene (e.g. aniline, dapsone and lidocaine). An asymptomatic, apparent ‘cyanosis’ is the earliest clinical feature, occurring when approximately 15% of total haemoglobin is replaced by methaemoglobin. Progressive manifestations of tissue hypoxia ensue at increasing methaemoglobin concentrations and concentrations approaching 80% may be fatal.

Keywords: aminobenzene, cyanosis, dapsone, haemoglobin oxidation, hypoxia, lidocaine, nitrobenzene, organic nitrites