Dehydration and oral or intravenous rehydration: Case

This 16-month-old presents with severe dehydration and a threatened circulation complicating acute gastroenteritis. The weight has fallen by about 11 percent, which is in the severe band above 10 percent, and his clinical dehydration scale is in the severe range with an irritable general appearance, very sunken eyes, dry mucous membranes, and absent tears. The capillary refill of 4 seconds, the tachycardia, and the oliguria for 14 hours indicate that the circulation is failing, and the serum sodium of 158 mmol per litre confirms hypernatraemic dehydration, which makes the speed of correction the dominant concern. The metabolic acidosis reflects poor perfusion and diarrhoeal bicarbonate loss. [11]

The immediate priority is to assess and support the circulation. I would manage him in a high-dependency or resuscitation area with continuous monitoring. His capillary refill of 4 seconds and oliguria indicate shock rather than simple dehydration, so I would give 10 to 20 mL per kg boluses of isotonic crystalloid, either 0.9 percent sodium chloride or a balanced crystalloid such as Hartmann solution, over 5 to 10 minutes, reassessing the perfusion after each bolus and repeating up to a total of 60 mL per kg before escalating to inotropes and intensive care. The bolus is reserved for the child whose perfusion has failed, which this child has. [11]

Once the circulation is restored, I would manage the hypernatraemia carefully. The brain has accumulated idiogenic osmoles to defend its volume, so a rapid fall in serum sodium draws water into the brain and causes cerebral oedema, seizures, and potentially death. I would use isotonic crystalloid rather than a hypotonic solution, and I would aim to lower the sodium no faster than 0.5 mmol per litre per hour, with a daily ceiling of 8 to 12 mmol per litre, rechecking the sodium every 2 to 4 hours initially and titrating the fluid to the rate of fall. Free water and rapid correction are avoided at all costs. I would monitor his conscious level for the early signs of cerebral oedema, which are headache, vomiting, drowsiness, and seizures. [10]

Potassium would be added to the fluid only after the serum sodium has begun to normalise and he has passed urine, because his potassium is already low and adding potassium too early risks hyperkalaemia in an oliguric child. Once his clinical signs have resolved and his sodium is trending down safely, I would move onto maintenance fluid following the Holliday and Segar formula of 100 mL per kg for the first 10 kg and 50 mL per kg for the next 10 kg, with the 4-2-1 rule as the hourly equivalent, using an isotonic crystalloid with added potassium and dextrose rather than a hypotonic fluid, because NICE advises a sodium of 131 to 154 mmol per litre for maintenance and against the routine use of hypotonic fluids to prevent hospital-acquired hyponatraemia. [1]

As soon as he tolerates it, I would reintroduce oral feeding, including milk and his normal diet, alongside the intravenous fluid. A single dose of oral ondansetron may help control the vomiting once the oral route is re-established, and reduced-osmolarity oral rehydration solution can be used to cover ongoing losses. I would seek and treat the cause of the gastroenteritis, send a stool sample if the diarrhoea is bloody or prolonged, and exclude an alternative diagnosis such as diabetic ketoacidosis, sepsis, or a surgical cause, which the history, the normal glucose, and the absence of bilious vomiting make unlikely. [8]

The prognosis is excellent with prompt and careful rehydration, and most children recover fully within a day or two, with the poor outcomes concentrated in the child whose hypernatraemia is corrected too fast. The discharge plan would address the gradual return to a normal diet, the warning signs of drowsiness, persistent vomiting, and reduced urine output that should bring the family back, and the prevention of the next episode through hand hygiene and rotavirus vaccination. I would counsel the family that the oral rehydration solution works even when there is diarrhoea, that small frequent sips are the key to home management, and that most children recover completely. [7]