Acute gastroenteritis and infectious diarrhoea — branching viva

Opening — framing the problem

The examiner begins: an 18-month-old has two days of watery diarrhoea and vomiting, is restless with sunken eyes and a slow skin pinch, but is alert with warm peripheries. Talk me through your approach. [1] [3]

I would frame this as acute gastroenteritis and make my first task the grading of dehydration, because that decides everything. The combination of sunken eyes, dry mucosa, a slow skin pinch and prolonged capillary refill in an alert child with warm peripheries fits some, or mild-to-moderate, dehydration rather than shock. I would rehydrate him orally while excluding a surgical mimic. [3] [1]

Branch A — the mechanism

Why does he become dehydrated, and why will oral rehydration solution help even though his gut is pouring out fluid? [8]

He is losing water and electrolytes in the stool faster than he can replace them, because a virus such as rotavirus damages the absorptive villi and drives active secretion. Oral rehydration solution works because the sodium-glucose co-transporter on the enterocyte stays intact; supplying sodium and glucose together drives their coupled absorption and water follows osmotically, so fluid is pulled back into the body despite the ongoing secretion. [8] [1]

Branch B — designing the rehydration

How exactly would you rehydrate him, and what if he will not drink? [1]

I would use low-osmolarity oral rehydration solution, giving roughly fifty to one hundred millilitres per kilogram over four hours as small, frequent sips, then reassess his hydration. Low-osmolarity solution is preferred because it reduces stool output, vomiting and the need for a drip. If he refuses or vomits repeatedly, I would pass a nasogastric tube and give the solution that way, because nasogastric rehydration works as well as intravenous fluid and avoids the complications of a drip. [8] [1]

Branch C — adjuncts and feeding

The vomiting is limiting his oral intake. What adjuncts would you use, and what about feeding? [13]

I would give a single dose of ondansetron, which reduces vomiting and the need for intravenous fluids and admission and often allows oral rehydration to succeed. I would add zinc for ten to fourteen days where indicated, resume his normal feeds early without diluting them and continue any breastfeeding, and I would avoid antidiarrhoeal drugs such as loperamide in a child this age. [13] [5]

Branch D — the pivot to bloody diarrhoea

Now a 4-year-old presents with bloody, mucoid, febrile diarrhoea. Does that change your thinking? [11]

Yes. Bloody diarrhoea points to an invasive or Shiga-toxin organism such as Shigella, Campylobacter, non-typhoidal Salmonella or enterohaemorrhagic Escherichia coli, so I would send stool and think carefully about antibiotics rather than give them reflexively. I would treat confirmed shigellosis or the systemically unwell child, but I would withhold antibiotics if enterohaemorrhagic Escherichia coli is possible, because they may increase the risk of haemolytic uraemic syndrome. [11] [1]

Closing — the safety rule

Give me the single safety point you would emphasise in the bloody-diarrhoea child. [11]

I would watch actively for haemolytic uraemic syndrome by monitoring for pallor, bruising and falling urine output and checking a full blood count, blood film, urea and creatinine, and I would counsel the family to return urgently if the child becomes pale, passes less urine or deteriorates. I would not start empirical antibiotics for bloody diarrhoea without a clear indication. [11] [1]