What should you know about hypernatremic dehydration in neonates?

Newborns can become dehydrated when feeding is not transferring enough milk, feeds are missed, or fluid is lost through vomiting, diarrhoea or heat. Sodium can become concentrated as water is lost. A baby may have fewer wet nappies, strong-smelling or dark urine, a dry mouth, reduced alertness, unusual fussiness, poor feeding or weight loss. The imbalance can affect the brain, so home treatment with plain water or homemade fluids is unsafe.

Contact a maternity, paediatric or emergency service promptly if you are worried about feeding or hydration. Keep offering breastfeeds or correctly prepared formula while arranging advice, unless a clinician tells you otherwise. Do not dilute formula, add extra powder, or give water, juice or oral rehydration products without specific instructions. Clinicians may check weight, feeding, urine output and blood sodium, then replace fluid gradually and monitor the baby.

Seek emergency help for a baby who is difficult to wake, floppy, having a seizure, breathing abnormally, repeatedly vomiting, refusing feeds, or producing very few wet nappies. A sunken soft spot, cold or mottled skin, or marked weakness also needs urgent assessment. These signs can occur with serious dehydration and should not be judged by urine colour alone.

Ask how much the baby is feeding, how wet nappies should be monitored, whether weight and sodium need repeat checks, and which feeding plan is safe. Ask what symptoms should prompt a return to hospital and whether an illness such as gastroenteritis needs treatment.