Your eyes may fool you... Keep your differential diagnosis open.

Selected References

Aravindhan N, Chisholm DG. Sulfhemoglobinemia presenting as pulse oximetry desaturations. Anesthesiology. 2000;93:883–884.

Gharahbaghian L et al. Methemoglobinemia and Sulfhemoglobinemia in Two Pediatric Patients after Ingestion of Hydroxylamine Sulfate. West J Emerg Med. 2009 Aug; 10(3): 197–201

Ginimuge PR et al. Methylene Blue: Revisited. J Anaesthesiol Clin Pharmacol. 2010 Oct-Dec; 26(4): 517–520.

Mack E. Focus on diagnosis: co-oximetry. Pediatr Rev. 2007;28:73–4.

So T-Y et al. Topical Benzocaine-induced Methemoglobinemia in the Pediatric Population. J Pediatr Health Care. 22(6):335–339.