Dehydration and oral or intravenous rehydration: Viva

This infant presents with severe dehydration from acute gastroenteritis. The weight has fallen by about 10 percent, the clinical dehydration scale is in the severe band with a drowsy general appearance, very sunken eyes, dry mucous membranes, and absent tears, and the capillary refill of 4 seconds with oliguria signals a threatened circulation. The serum sodium of 149 mmol per litre is at the upper end of normal, just below the hypernatraemic threshold of 150, so the correction must be slow and isotonic to avoid cerebral oedema. The examiner will probe the severity grading, the route and the fluid, the rate of correction, and the feared complication. [11]

The dehydration is graded in three complementary ways. The percentage weight loss is about 10 percent, which places it in the severe band above 10 percent or at its boundary. The clinical dehydration scale scores general appearance, eyes, mucous membranes, and tears from zero to two, and a score of five to eight is moderate to severe, which fits. The World Health Organization classification groups children into no, some, and severe dehydration on the bedside signs, and the drowsiness and oliguria place this infant in the severe category. The severity grade selects the treatment arm at the point of the first assessment. [4]

The route is intravenous, not oral. Oral rehydration therapy is the first-line treatment for mild to moderate dehydration and is as effective as intravenous fluid, but this infant is severely dehydrated with a threatened circulation and is unable to protect the oral route reliably while drowsy, so intravenous rehydration is indicated. A child in frank shock would first receive 10 to 20 mL per kg boluses of isotonic crystalloid over 5 to 10 minutes, reassessed after each. This infant is borderline, so I would establish intravenous access, assess the perfusion carefully, and give an initial isotonic bolus if the circulation fails, then proceed to the staged protocol. [7]

The fluid is isotonic crystalloid, not hypotonic. After any shock is reversed, the NICE protocol gives 100 mL per kg of 0.9 percent sodium chloride without potassium over 10 hours for the standard case, but with a sodium of 149 mmol per litre I would manage the infant on the slow-correction pathway and recheck the sodium frequently, watching that it does not fall faster than 0.5 mmol per litre per hour with a daily ceiling of 8 to 12 mmol per litre. NICE advises an isotonic crystalloid with a sodium of 131 to 154 mmol per litre for maintenance and against the routine use of hypotonic fluids such as 0.45 percent sodium chloride or 5 percent glucose alone, because the antidiuretic hormone of the stressed state retains the free water and drives the sodium down. [10]

Potassium is added only after the sodium has normalised and the infant has passed urine. The maintenance volume follows the Holliday and Segar formula of 100 mL per kg for the first 10 kg, with the 4-2-1 rule of 4 mL per kg per hour for the first 10 kg as the hourly equivalent. The complication I most fear is cerebral oedema, which is iatrogenic and arises when the serum sodium is lowered too fast in hypernatraemia or when a hypotonic fluid is given. The prevention is the disciplined use of isotonic fluid, the controlled correction rate, and the frequent monitoring of the sodium and the conscious level. [10]

I would counsel the family on the warning signs of deterioration, the gradual reintroduction of feeding and breastfeeding once the infant tolerates it, and the general measures of hand hygiene and rotavirus vaccination that prevent the next episode. The prognosis of paediatric dehydration is excellent when it is recognised and treated promptly, and most children recover fully within a day or two of rehydration, with the poor outcomes concentrated in the child who presents late or whose sodium is corrected too fast. [11]