Dehydration and Hypoglycaemia: Managing the Infant with Gastroenteritis

Full strength milk can be given to the infant once fluids are tolerated or where the child is hungry: as young children with gastroenteritis are susceptible to hypoglycaemia.

The acutely unwell older infant (> 6 months old) can be rehydrated rapidly with 50 mL/kg oral rehydration therapy (ORT) over 4 hours, with the understanding that this is maximal enteral fluid replacement and that the occasional emit does not preclude from the use of ORT. A child who has been unwell for more than 48 hours will, however, need more gradual fluid replacement over 24 hours, in which case the clinician takes account also for maintenance and ongoing losses into their calculation.

To calculate the fluid deficit, a comparison of body weight is best; otherwise, approximate from clinical findings: an irritable, restless infant with sunken eyes and tachycardic is at least 5% of body weight dehydrated. The lethargic, peripherally shutdown, tachypnoeic infant with sluggish capillary refill (about 3 seconds) time is near 10% dehydrated.

Consider giving ondansetron 2 mg PO and start with 5 mL (1 tsp) bubble-gum Pedialyte¹ fluid per minute. Where ongoing losses exceed this, the child will need NGT or intravenous fluids: refer this child immediately to the ED. Or, if the ED is some time away, and you can, start 10 mL/kg/hr 0.9% NS + 5% D.

So then:

1. Deficit (mL) = % dehydration x body weight (kg) x 10
   • replace over 24 hours with isotonic fluid (e.g. Hartmann’s)
2. Maintenance: give as isotonic fluid at one of the following rates:
   • 3-10 kg: 4 mL/kg/hr
   • 10-20 kg: (40 + 2) mL/kg per hour
   • > 20 kg: (60 + 1) mL/kg per hour
3. Ongoing losses = 2 mL/kg/hour, in acute gastroenteritis
   • replace proactively with 4%D + N/5 over 24 hours
     • i.e. calculate the expected daily loss over the next 24 hours and replace in real time

Good.

Shock: If the child is hypotensive or acidotic, forget all that and just go straight for a 10 mL/kg 0.9% NaCl bolus first up. That child is shocked and needs immediate resuscitative crystalloid. This is the rule for all except those children with presumed ICH, encephalitis/ meningitis, those with bronchiolitis/ pneumonia, or if suspected hyper/hyponatraemic, in which case, because of significant SIADH, deficit replacement is more gradual, over 48 hours, and the calculated maintenance fluid amount is reduced by one-third (i.e. to ~ 60% maintenance).

But if the child has a high fever, has capillary leak (e.g. allergy, sepsis), or third spacing (bowel obstruction), then requirements again are increased. In these children, look for rapid weight gain (> 5% per day) or eyelid or lower limb oedema as signs of fluid overload and pare back on the rate of fluid administration and maybe check electrolytes, serum sodium in particular.

But if you’re managing to get the fluids in orally and the child is taking in only water, consider also to check the BGL, particularly in the young infant or where there are large ketones in the urine or the child is lethargic; and treat if BSL < 3.0 mmol/L. Give this child 5 mL/kg of 10% Dextrose IV. If you cannot do that, feed the child milk.

At Day 1, it is 60 mL/kg (80 in a preterm) of fluid needs, and this need increases by 20 mL/kg each day until a target of 150-170 mL/kg/day of fluid volume is reached. You can give this as either breast milk or bottle feeds. [The maximum glucose oxidation rate is 12 mg/kg/min for a term child and 6-8 mg/kg/min for a preterm child].

Note that:

• 5% Glc: 5 g in 100 mL
  • 10% Glc: 10 g in 100 mL
• 1 g Glc = 3.8 kcal (15.9 kJ)
• e.g. An infant of weight 6 kg can metabolise a maximum of 72 mg Glc every minute, so that 100 mL of 5% Glc (or 19 kcal) should be given over an hour (70 minutes). An infant at 3 months of age requires 220-240 kJ (57 kcal) per day, so that total daily energy requirements (equiv. to 15 g Glc) can be given over about 3 hours.

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1. Pedialyte^® is a therapeutic oral hydration solution that replenishes vital minerals and nutrients lost during diarrhoea and vomiting and to help prevent mild to moderate dehydration in infants, children and adults.

Refer to the Paediatric Handbook (9th Edn), by Gwee, Rimer, and Marks for more.