[A woman in her 40s with declining consciousness after initiation of enteral feeding]

Hyperammonaemic encephalopathy is a potentially life-threatening condition usually caused by liver failure, but it can also occur despite normal liver function tests, making diagnosis challenging.

A woman in her forties with prior gastric sleeve bypass (SASI) was admitted to hospital for weight loss, oedema and fatigue. Enteral nutrition via a feeding tube was initiated. A few days later, the patient was readmitted and became comatose. Her ammonia level was elevated at 298 μmol/L despite normal liver function tests. She was intubated and transferred to the ICU for treatment with dialysis, sodium benzoate, lactulose and rifaximin. Enteral nutrition was paused, and she was given glucose to prevent catabolism. Urea cycle disorders were excluded. Vitamins and minerals were supplemented. After nine days, epileptic activity ceased on EEG, ammonia levels normalised, and the patient was extubated in good condition.

Non-hepatic hyperammonaemia (NHHA) is rare and can result from primary or secondary urea cycle disorders. In this case, increased ammonia production resulted from high protein intake and muscle breakdown, while reduced elimination was due to secondary urea cycle impairment caused by post-surgery undernutrition. Clinicians should consider screening for hyperammonaemia in critically ill patients with new-onset encephalopathy, seizures or refractory vomiting despite normal liver function tests.