dehydration in infants

Last reviewed 03/2021

The water loss associated with conditions such as gastroenteritis can impose a relatively greater stress on the young infant due to the higher percentage of body water when compared to an adult (1) (a term baby is 80% water, which reduces to a proportion of 60% at a year).

In children water as a percentage of body weight is higher than in adults (1). However children are at greater risk for dehydration than adults due to:

• their higher surface to mass ratio
• difference in thirst sensitivities and body cooling mechanisms (2).

Infants are more vulnerable to fluid and electrolyte imbalance than adults due to the following factors:

• high surface-to-body-weight ratio
• limited ability to excrete solutes and to concentrate urine
• low ability to express thirst
• high metabolic rate (1)

The following patients are at increased risk of dehydration:

• children younger than 1year, particularly those younger than 6 months
• infants who were of low birth weight
• children who have passed more than five diarrhoeal stools in the previous 24 hours
• children who have vomited more than twice in the previous 24 hours
• children who have not been offered or have not been able to tolerate supplementaryfluids before presentation
• infants who have stopped breastfeeding during the illness
• children with signs of malnutrition (3)

Fever (due to increased insensible water loss), vomiting, diarrhoea and the use of formula not diluted appropriately may result in dehydration in infants.

It is very important to note that it is both easy for an infant to become dehydrated, and easy to rehydrate that infant with oral rehydration therapy in the vast majority of cases.

Reference:

• (1) Jéquier E, Constant F. Water as an essential nutrient: the physiological basis of hydration. Eur J Clin Nutr. 2010;64(2):115-23
• (2) D'Anci KE, Constant F, Rosenberg IH. Hydration and cognitive function in children. Nutr Rev. 2006;64(10 Pt 1):457-64
• (3) National Institute for Health and Clinical Excellence (NICE) 2009. Diarrhoea and vomiting in children. Diarrhoea and vomiting caused by gastroenteritis: diagnosis, assessment and management in children younger than 5 years