Methaemoglobinaemia – Clinical Case 2

A 47 year old Afro-Caribbean male is brought in by ambulance as a red standby with reduced GCS and hypoxia. His wife tells you he was well earlier and this morning had a tooth removed at the dentist. When he came home he started complaining of a headache and became groggy. He has problems with his heart and takes heart medicines that he’s been on for a few years.

The ambulance gave 15L of oxygen via a NRB mask as sats were 85%. They have not improved. He is lethargic but is maintaining his own airway and his GCS is 14/15 (E3 V5 M6). He is tachycardic, apyrexial and normotensive. ECG is unremarkable. You suspect methaemoglobinaemia and the diagnosis is quickly confirmed on ABG – his MetHb is 28%. You also note his Hb is 9.9.

You decide to give this patient Methylene Blue. What factors have you considered when making this decision?

You give Methylene Blue and there is no improvement. You give another dose and there is still no response. His Hb has now fallen to 7.5 and he is less responsive. Why?

What is your next step?

What is the most likely cause of this patient’s methaemoglobinaemia?