Case 1

A 20 month old girl presented with a short history of vomiting, cough, and anorexia. She had attended the accident and emergency department on four occasions—with a viral illness, urinary tract infection, pertussis, and breath holding. She was admitted for observation, and a provisional diagnosis of viral illness was made. The girl refused solid food but took fluids well over the next 48 hours. At this time she had a tonic seizure associated with apnoea but responded to treatment with rectal diazepam. Biochemical investigations showed serum sodium concentration 116 mmol/l, chloride 84 mmol/l, potassium 2.8 mmol/l, urea 2.8 mmol/l, and creatinine 35 mmol/l.

The patient's fluid intake was restricted to 60% of the maintenance requirement, but four hours later she had a further tonic seizure associated with decerebrate posturing. She was intubated and ventilated and given intravenous mannitol and phenytoin. Computed tomograms of the brain showed diffuse cerebral oedema (figure). Her urine output over the next 12 hours was approximately 12 ml/kg per hour, and with fluid restriction her serum electrolyte values returned to normal. Repeat computed tomography 24 hours later showed appreciable improvement, with normal basal cisterns …