Management of Nitrobenzene Compound Poisioning – A Case Report

INTRODUCTION: Nitrobenzene injection results in methaemoglobinemia causing cyanosis desaturation and death. CASE REPORT: A 60 year old male consumed nitrobenzene 20% along with 300 mL alcohol. He was brought to casualty in a drowsy state and looked cyanosed. BP was 160/90 mmhg, pulse rate was 60bpm, and Spo2 was 80% on room air. In view of progressive deterioration of GCS and desaturation, patient was intubated and put on SIMV with pressure support (PS) and Fio2 80%, RR of 16, TV of 400 mL, PEEP of 5cmH2O, pressure support of 16cmH2O and was shifted to MICU. ABG had a chocolate brown appearance with pH 7.27, pCo2 50 mmhg, Hco3 17mEq/L and Spo2- 85%. Nitrobenzene poisoning causing methaemoglobinemia was treated with injection methylene blue 1% 50 mg 6th hourly. The right side internal jugular vein was cannulated along with left sided radial artery. Urine output was maintained. On investigation Hb was10 gm% and other blood parameters were within normal range. Intravenous methylene blue improved Spo2 to 97% over the next 30 minutes only to return to 85% in the next 3 hours, with a similar response to another dose. Two units of fresh blood were transfused which improved the Spo2 from 92% to 94%. On day 3, patient was conscious. Vital signs were maintained. On day 4, methylene blue was stopped in view of improved Spo2 (94-100%) with fio2 of 0.4% and patient was extubated. Patient was maintaining Spo2 of 95% on room air. DISCUSSION: Methaemoglobin level of 10 to 15%, leads only to cyanosis. When it exceeds 20%, it leads to multiple signs and symptoms including headache, breathlessness, chest pain, increased respirations, and tachycardia. When it reaches 40 to 50%, confusion, lethargy, and metabolic acidosis occur which will ultimately lead on to seizures, bradycardia, ventricular dysarrthymia, hypertension, and coma. The levels around 70% are fatal.(1,2,3) Methylene blue, 1 to 2 mg/kg is administered as a 1% solution IV over 3 to 5 minutes, repeated at 1 mg/kg in 1 hour as necessary. Methylene blue can also cause false SpO(2) levels. This antidote is toxic at doses more than 7 mg/kg and can cause breathlessness, chest pain, and haemolysis.(3,4) CONCLUSION: Acute methemoglobinemia is usually associated with high mortality; hence, an early aggressive management of poisoning should be attempted.