[Infant with cyanosis and hypoxemia].

We report on an 8-week-old infant who presented as an outpatient due to abnormal skin color a few hours after surgical achillotomy under local anesthesia. The infant showed a dirty brownish, cyanotic skin color with reduced general condition and hypoxemia at SaO2 84% without improvement by oxygen supplementation. The blood gas analysis showed lactic acidosis and a significantly elevated methemoglobin level of 38% (reference value≤1.5%). Due to the temporal correlation, this is most likely due to the infiltration anesthesia with mepivacaine, which was performed for the achillotomy. Treatment with methylene blue was administered, resulting in a restitutio ad integrum.Methemoglobin is formed by the oxidation of iron contained in hemoglobin, which prevents oxygen from binding. Significant cyanosis can occur when the methemoglobin level exceeds 10%. The reduction of methemoglobin to oxyhemoglobin by the enzyme NADH cytochrome b5 reductase is physiologically not fully developed in young infants. Furthermore, the hemoglobin of young infants is more easily oxidized, which makes these children susceptible to methemoglobinaemia. As the methemoglobin content increases, the blood turns brown with increasing levels of methemoglobin, which is visible clinically and in blood samples.Local anesthetics applied cutaneously, subcutaneously or mucous membranes can cause clinically relevant methemoglobinemia, which can result in potentially severe hypoxemia. The risk is increased in young infants. It is important to recognize methemoglobinemia as the cause of cyanosis in time, as it is easily treatable.