Abstract
Methaemoglobinaemia is an unusual cause of cyanosis whether it is congenital or acquired. Hence, the diagnosis may not be immediately obvious and appropriate treatment may be delayed. The case described shows that it should be considered when pulse oximetry and arterial blood gas analysis appear to give conflicting results. A healthy 24-yr-old woman was found to have a pulse oximeter reading of 82% prior to induction of anaesthesia for minor surgery. Clinical examination confirmed cyanosis but no other abnormality was detected. She had no important medical history and was not receiving any medications. Arterial blood gas analysis with the patient breathing air showed PaO2 12.03 kPa (90 mmHg). Co-oximeter analysis of this sample revealed a methaemoglobin content of 13.4% and she was subsequently found to have congenital methaemoglobin reductase deficiency. Anaesthesia was induced and maintained with incremental doses of propofol and fentanyl. A spontaneously breathing technique with oxygen in nitrous oxide was employed uneventfully. No specific treatment for methaemoglobinaemia was given. Perioperative pulse oximetry is one of the major advances in patient monitoring in recent years but unexpected results should not be accepted uncritically. A knowledge of the working principles of oximetry is essential to enable appropriate management in the presence of dyshaemoglobins.
Résumé
La methémoglobinémie est une cause rare de cyanose congénitale ou acquise. Le diagnostic peut ne pas être immédiatement manifeste et son traitement peut être retardé. Cette observation montre qu’il faut y penser quand l’oxmyétrie puisée et les gaz du sang artériel semblent se contredire. L’oxymétrie pulsée d’une femme de 24 ans bien portante indique 82% de saturation avant l’induction de l’anesthésie pour une chirurgie mineure. L’examen clinique confirme la cyanose mais on ne décèle pas d’autre anomalies. L’anamnèse est sans particularité et la patiente ne reçoit aucun médicament. Lorsque la patiente respire de l’air, l’analyse des gaz du sang artériel montre une PaO2 de 12,03 kPa (90 mmHg). L’analyse au co-oxymètre de l’échantillon révèle un contenu en methémoglobine de 13,4%. Par la suite, on diagnostique une déficience congénitale de la methémoglobine réductase. L’anesthésie est induite et entretenue avec des doses répétées de propofol et de fentanyl. Une technique de respiration spontanée avec de l’oxygène dans du protoxyde d’azote est utilisée sans incident. On n’administre pas de traitement spécifique pour la methémoglobinémie. Ces dernières années, l’oxymétrie puisée peropératoire a représenté un des progrès majeur du monitorage mais des résultats inattendus ne doivent pas être acceptés sans discernement. Une connaissance des principes de l’oxymétrie est essentielle pour une conduite appropriée en présence d’une dyshémoglobinémie.
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Chisholm, D.G., Stuart, H. Congenital methaemoglobinaemia detected by preoperative pulse oximetry. Can J Anaesth 41, 519–522 (1994). https://doi.org/10.1007/BF03011548
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DOI: https://doi.org/10.1007/BF03011548