[Pulse oximetry and methemoglobinemia].

Background: Cyanosis associated to low oxygen saturation may reveal hemoglobin pathology.
Case Report: A 3 year-old child had a nephroblastoma with pleural effusion. He suddenly developed persistent cyanosis despite pleural effusion drainage; transcutaneous and measured oxygen saturations were low and PaO2 on arterial blood gases was high. Methemoglobinemia was diagnosed, due to prilocaine-lignocaine cream used for local anesthesia, associated to partial G6PD deficiency. The methemoglobinemia disappeared after methylene blue treatment.
Conclusion: Cyanosis with low oxygen saturation and high or normal PaO2 should lead to the search of a hemoglobin pathology, especially methemoglobinemia, by appropriate methods.