You are called urgently to resus over the tannoy.

You arrive to find the senior nurse beckoning for you to come over and see a 3-year old child who has been brought in by her mother.

The child has cerebral palsy secondary to birth asphyxia and is known to have epilepsy in the past. She is PEG normally fed by her parents who look after at home.

Over the last 3 days sshe has been increasingly unwell with diarrhoea (up to 12/day) and vomiting. Quite rightly, and on the advice of the GP she has continued to be fed during this time, though no increas in feeds has been instituted.

It is difficult to assess her urinary output as she wears nappies which have been contaminated with the diarrhoea.