Methaemoglobinaemia due to nitrobenzene poisoning

Abstract

An acute poisoning with nitrobenzene presenting as methaemoglobinaemia is an uncommon medical emergency. Here, we report the case of a 33-year-old male presenting with an alleged history of consumption of an unknown substance 24 h ago. On admission, he was unconscious (Glasgow Coma Scale score 3) and gasping. General physical examination revealed cyanosis of the fingers, lips and tongue, pulse: 128/min, blood pressure: 98/70 mmHg and arterial oxygen saturation by pulse oximeter (SpO2): 70%. Pupils on both sides were dilated and sluggishly reacting to light. Respiratory system examination revealed bilateral basal crepitations. Rest of the physical examination was normal. Tracheal intubation was done, and he was initiated on mechanical ventilator support. Arterial blood gas analysis showed pH: 7.28; arterial carbon dioxide tension (PaCO2): 29.9 mmHg, arterial oxygen tension (PaO2): 45 mmHg, arterial oxygen saturation (SaO2): 83.8% and bicarbonate: 13.4 mEq/L. In spite of mechanical ventilator support, he continued to have hypoxia and cyanosis. Saturation gap was calculated to be 13%. In view of which methaemoglobinaemia was considered and blood sample has been sent for methaemoglobin levels and started him on injectable methylene blue and ascorbic acid. After a week, hypoxia and cyanosis improved and he was discharged in a haemodynamically stable condition.

Keywords

• methaemoglobinaemia
• nitrobenzene
• saturation gap