Metabolic encephalopathy caused by nitrous oxide (‘laughing gas’) induced hyperammonaemia

A 26-year-old man presented at the emergency department with confusion and decreased consciousness after several days of vomiting. In the preceding 6 months, he had used a 2-litre tank of nitrous oxide (N 2 O) weekly. His metabolic encephalopathy was caused by hyperammonaemia which probably resulted from interference of N 2 O-induced vitamin B 12 deficiency with ammonia degradation. A catabolic state might have contributed to the hyperammonaemia in this case. After treatment with vitamin B 12 and lactulose, both his consciousness and hyperammonaemia improved. He reported no residual complaints after 3 months of follow-up. Since N 2 O is increasingly used as a recreational drug, we recommend considering hyperammonaemia as a cause of metabolic encephalopathy in cases of N 2 O use and altered mental status.