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]

Question 2 (10 marks)

Describe the clinical dehydration scale and the percentage weight loss bands, explain the composition and the principle of reduced-osmolarity oral rehydration solution, and state when oral rehydration therapy is preferred over intravenous fluid. [4]

The clinical dehydration scale scores four findings, each from zero to two, for a total from zero to eight. General appearance is zero when normal, one when thirsty or restless or lethargic but consolable, and two when drowsy or limp or poorly responsive. The eyes are scored as normal, slightly sunken, or very sunken, the mucous membranes as moist, sticky, or dry, and the tears as normal, reduced, or absent. A score of zero is no dehydration, one to four is some or moderate dehydration, and five to eight is moderate to severe dehydration. The percentage weight loss bands are mild below 5 percent, moderate 5 to 10 percent, and severe above 10 percent. This boy, with a 9 percent weight loss and a high score, sits at the moderate to severe boundary, which is consistent with his presentation. [4]

Reduced-osmolarity oral rehydration solution has an osmolarity of about 245 mOsm per litre, a sodium of 75 mmol per litre, a glucose of 75 mmol per litre, and a potassium of 20 mmol per litre. It replaced the older standard solution of 311 mOsm per litre with 90 mmol per litre sodium because the lower osmolarity improves absorption through the sodium-glucose cotransporter in the intestinal brush border and reduces stool output and the need for intravenous fluid without provoking hypernatraemia. The principle is that the coupled absorption of sodium and glucose drives the absorption of water even in the face of continuing secretory diarrhoea, so that the solution works when plain water would not. For moderate dehydration, 50 mL per kg is given over 4 hours in addition to ongoing losses, by spoon or syringe as 5 mL every one to two minutes. [7]

Oral rehydration therapy is the first-line treatment for mild to moderate dehydration, and the Cochrane review by Hartling and colleagues confirmed that it is as effective as intravenous fluid in correcting the deficit while avoiding the cannula, the admission, and the complications. A single dose of oral ondansetron reduces vomiting and the need for intravenous rehydration and is the standard adjunct that makes oral therapy feasible. Intravenous rehydration is reserved for the child who fails oral therapy, who has moderate to severe dehydration such as this boy, who is hypernatraemic or hyponatraemic, or who is in shock. The decision between the two routes is therefore made at the bedside on the severity, the sodium, and the response to an oral trial. [7]