Gastroenteritis and Oral Rehydration in Children

❍ Dehydration assessment and ORS management

Assess dehydration using clinical signs. Children under 2 and infants are at highest risk because of their higher fluid-to-body-mass ratio and limited ability to self-regulate intake.

No clinically detectable dehydration: alert and active, moist mucous membranes, normal skin turgor, normal urine output, normal capillary refill. Management: ORS at home with clear parental safety-netting.

Clinical dehydration (approximately 3-8%): appears unwell or irritable, dry mucous membranes, reduced skin turgor, eyes slightly sunken, fewer than 3 wet nappies per day or no urine for over 8 hours, capillary refill 2-3 seconds. Management: supervised ORS in clinic; hospital if unable to tolerate.

Severe dehydration (approximately 8-10% or above): lethargic, very sunken eyes, absent tears, markedly reduced skin turgor, capillary refill over 3 seconds, tachycardia, cool peripheries, weak pulse. Management: urgent IV access and fluid resuscitation; hospital admission.¹

Serum electrolytes are required in children with clinical or severe dehydration, and in any child with altered consciousness or signs of shock. Stool culture is not required in uncomplicated gastroenteritis; consider if blood is present in stool, if there is high fever, or after overseas travel.

ORS rehydration schedule: give 5-10 mL by spoon or syringe every 1-2 minutes - children often tolerate small frequent volumes even when vomiting. For mild dehydration: 50 mL/kg ORS over 4 hours. For clinical dehydration: 100 mL/kg ORS over 4 hours with close monitoring.

Feeding: continue breastfeeding throughout illness. Resume a normal age-appropriate diet as soon as tolerated; do not withhold solid food for more than 4-6 hours once oral rehydration is established. Full-fat dairy and fruit are well tolerated in most cases.

❍ Ondansetron, other agents, and admission criteria

Ondansetron (a 5-HT3 receptor antagonist) reduces vomiting frequency and decreases hospitalisation rate in children with moderate gastroenteritis.² It is used in NZ emergency departments and increasingly in primary care. Dosing: 0.15 mg/kg orally (max 8 mg), single dose; may be repeated once after 8 hours. As of 2024, ondansetron is not funded for outpatient use in NZ - families may need to purchase it at cost. Not routinely recommended in infants under 6 months or in children with suspected surgical abdomen.

Probiotics have inconsistent evidence; the most studied strains (Lactobacillus rhamnosus GG, Saccharomyces boulardii) may modestly reduce duration of diarrhoea but are not a substitute for ORS.³ Loperamide is contraindicated under 2 years and not recommended under 12.

Refer to secondary care for: severe dehydration (shock, significantly altered consciousness, no urine for over 12 hours); clinical dehydration failing to improve after 4 hours of supervised ORS; inability to tolerate any oral fluids despite ondansetron; age under 3 months with significant symptoms; bloody diarrhoea with high fever or toxic appearance (consider haemolytic uraemic syndrome); suspicion of a surgical cause (bilious vomiting, abdominal distension, right iliac fossa tenderness). Safety-net all children managed at home: return if the child develops any red features, reduced consciousness, more than 8 episodes of diarrhoea per day, persistent vomiting despite ondansetron, or parental concern that the child is not improving.