Hyponatraemia and hypernatraemia — formative SAQs

SAQ 1 (10)

A 3-year-old boy is admitted with pneumonia and receives 0.45 percent saline with dextrose as maintenance fluid. On day two he has a headache, vomits and then has a generalised seizure. His serum sodium is 116 mmol/L. ^[2]

1. Name the likely complication and give the emergency treatment, with dose, route and repeat rule. (4) ^[2]
2. A colleague suggests a benzodiazepine alone and worries that hypertonic saline needs a central line. Respond with evidence. (3) ^{[2] [3]}
3. How would you prevent this in the next child admitted with pneumonia? (3) ^[5]

Model answer

Complication and emergency treatment. Headache, vomiting and a seizure with a sodium of 116 mmol/L suggest hyponatraemic encephalopathy. Ayus and Moritz treat it with a 2 mL/kg bolus of 3% NaCl, repeated 1 to 2 times if symptoms persist. A single bolus raises the serum sodium by at most about 2 mEq/L. ^[2]

Responding to the colleague. In the Sarnaik series, 28 children treated with a benzodiazepine or phenobarbital had 13 treatment failures and 10 episodes of apnoea, whereas 3% saline resolved seizures and apnoea in all cases. Ayus and Moritz state that hypertonic saline can be given safely through a peripheral vein outside intensive care. They also state that acute hyponatraemia carries no significant risk of cerebral demyelination. ^{[3] [2]}

Prevention. Ayus and Moritz advise avoiding hypotonic intravenous fluids in hospital patients with possible non-osmotic stimuli for vasopressin. The AAP recommends isotonic maintenance fluid with appropriate potassium chloride and dextrose for patients aged 28 days to 18 years, because it significantly decreases the risk of hyponatraemia. The number needed to treat to prevent hyponatraemia was 7.5. ^{[2] [5]}