Causes of central cyanosis [1, 2, 7]
Cardiac	∙ Hemodynamic pulmonary edema
	∙ Cardiac malformations with arteriovenous shunt
Pulmonary	∙ Pneumonia
	∙ Respiratory insufficiency
	∙ Pulmonary embolism
Methemoglobinemia
Congenital	∙ NADH diaphorase enzyme deficiency, transmitted in an autosomal recessive mode, in these subjects the methemoglobin level varies between 20% and 45%
	∙ Structural abnormalities of hemoglobin that will favor the ferric form of heme
Nonorganic causes	∙ Poppers, nitrates (plant fertilizers, Ajax), gunpowder, chlorates
Organic causes	∙ Anesthetics (benzocaine, lidocaine, prilocaine) quinines and derivatives, metoclopramide, sulfonamides and sulfone (dapsone), phenazopyridine, phenylacetamide and derivatives, aminobenzene (aniline, naphthalene), nitrobenzene and derivatives, nitrotoluene.