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Poisoning with inhalational nitrites is a recognised cause of methaemoglobinaemia presenting to the emergency department. Methaemoglobin (MetHb) is the oxidised form of haemoglobin and incapable of carrying oxygen. The concentration of MetHb does not exceed 1%–2% in the normal physiological state. Previously reported cases 1,2 include patients with severe poisoning who were comatosed on presentation or required repeat treatment with methylene blue (MB). Two cases of severe methaemoglobinaemia secondary to misuse of amyl nitrite are presented. A MetHb level of greater than 50% was measured in each case, however, both patients were conscious and talking on presentation and showed clinical and biochemical response to treatment with one dose of MB.
CASE REPORT 1
A 32 year old white woman was brought by ambulance to the emergency department. She had been found “collapsed” on the street but was alert and appropriately responsive. She admitted sniffing half the contents of a small bottle of amyl nitrite, drinking one unit of alcohol, and smoking cocaine. On examination a deep blue-grey discoloration was noted of her skin especially over the lips, nose, and ears despite 15 l/min high flow oxygen therapy. A pulse oximetry reading of 82%, together with a pulse rate of 130 beat/min, blood pressure 100/50 mm Hg, and a respiratory rate of 22 breaths/min were noted. Neurological examination was unremarkable with a Glasgow coma score of 15, no focal neurology, and normally reactive pupils.
An arterial blood sample was chocolate brown coloured and had a MetHb level …