Dehydration and oral or intravenous rehydration: SAQ

This boy presents with moderate to severe dehydration complicating acute gastroenteritis, and the serum sodium of 156 mmol per litre places him in the hypernatraemic category that governs the speed of correction. His weight has fallen by about 9 percent, which is at the moderate to severe boundary, and his clinical dehydration scale is high, with reduced general appearance, sunken eyes, dry mucous membranes, and reduced tears. The capillary refill of 3 seconds and the oliguria suggest a threatened circulation, though he is not yet in frank shock. The metabolic acidosis reflects poor perfusion and diarrhoeal bicarbonate loss. The single most important feature is the sodium, because a rapid correction would risk cerebral oedema. ^[11]

Question 1 (10 marks)

Outline the immediate assessment and management of this child, including the decision between oral and intravenous therapy, the intravenous fluid regimen, and the management of his hypernatraemia. ^[11]

I would first assess the airway, breathing, and circulation and treat any shock. His capillary refill of 3 seconds is prolonged, and although he is not frankly shocked, I would monitor him closely. A child in shock would receive 10 to 20 mL per kg boluses of isotonic crystalloid over 5 to 10 minutes, reassessed after each. Because his perfusion is borderline rather than failed, I would not give a routine bolus, but I would be ready to if he deteriorates. I would establish intravenous access and send a full set of bloods including a repeat sodium, potassium, renal function, venous gas, glucose, and a full blood count. ^[11]

Because of the degree of dehydration and the hypernatraemia, I would manage him with intravenous rather than oral rehydration. I would use the NICE protocol adapted for hypernatraemia, giving isotonic crystalloid rather than a hypotonic solution. I would give 0.9 percent sodium chloride without potassium over the first phase of rehydration, aiming to correct the deficit slowly. The serum sodium must fall no faster than 0.5 mmol per litre per hour, with a daily ceiling of 8 to 12 mmol per litre, because his brain has accumulated idiogenic osmoles and a rapid fall would draw water into the brain and cause cerebral oedema, seizures, and potentially death. I would recheck the sodium every 2 to 4 hours initially and titrate the fluid to the rate of fall. ^[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 at the lower end of normal and adding potassium too early risks hyperkalaemia in an oliguric child. I would monitor his conscious level closely for the early signs of cerebral oedema, which are headache, vomiting, drowsiness, and seizures. I would correct the hypoglycaemia if present, though his glucose is normal. Once his clinical signs have resolved, his sodium is trending down safely, and he is passing urine, I would move onto maintenance fluid following the Holliday and Segar formula of 100 mL per kg for the first 10 kg, with the 4-2-1 rule as the hourly equivalent, and reintroduce oral feeding including breastfeeding as soon as he tolerates it. ^[1]