Rehydration of children: causes of dehydration, solutions, and prevention

Dehydration is one of the most common emergencies in children, especially in cases of gastroenteritis or heat waves. Knowing how to quickly identify the signs and having the right rehydration reflexes often prevents worsening and hospitalization. This guide reviews children's fluid needs, the most common causes of dehydration, and various rehydration solutions, from a simple glass of water to oral rehydration solution.

1. Understanding a Child's Fluid Needs

A child is growing, which implies particular needs for nutrients and water. The European Food Safety Authority (EFSA) has established nutritional reference values to follow for hydration:

These are recommendations to cover water needs under moderate ambient temperature conditions and during normal physical activity. These values are minimum thresholds, which may be insufficient in cases of high heat, for example. It is then important to ensure that children have regular access to water so that they can drink whenever they feel the need. In overweight or obese children, fluid needs may also be higher.

Furthermore, it is important to know the signs of dehydration in infants and children to be able to intervene quickly and restore hydration. Since infants cannot yet identify and express their need for water, they require particular attention from those around them. Here are the symptoms to be aware of in infants:

• Dry mouth, often accompanied by a lack of saliva. The appearance of the lips can facilitate its identification.
• Fewer wet diapers or the need to change fewer than 4 diapers per day.
• Abnormal sunkenness of the anterior fontanelle (soft spot on the head).
• Crying without tears.
• Drowsiness or unusual irritability.

These signs evolve as the child grows (from 2 to 7 years old). Even if they can express their thirst or symptoms more easily, it is still necessary to remain attentive in the following cases:

• Intense thirst.
• Very dark and infrequent urine.
• Dizziness and fatigue.
• Dry, dark-circled, or sunken eyes.
• Confusion and abnormal irritability.
• Sticky or dry oral mucous membranes (tongue, lips).

A sudden decrease in weight is also a warning sign. In children, dehydration can occur with a loss of just 2% of body weight, and becomes severe beyond 5%. When the loss exceeds 10%, the situation is critical: the functioning of vital organs is compromised, which requires urgent medical attention.

2. Common Causes of Dehydration in Children

Certain situations expose children to a high risk of dehydration. The main causes are excessive losses or insufficient water intake.

Diarrhea and vomiting, common in cases of gastroenteritis, are among the most worrying causes. These rapid digestive losses lead to a significant loss of water and electrolytes. However, in children, the sensation of thirst is not always sufficient to spontaneously compensate for these losses: it is therefore essential to encourage them to drink. At the same time, food intake should not be interrupted, as it remains crucial to limit the associated risks of malnutrition. It is then preferable to avoid foods that are difficult to digest or laxative, such as some green vegetables or acidic fruits. Instead, favor anti-diarrhea foods, such as rice, ripe bananas, and apple sauce.

Another major cause of dehydration is perspiration, which naturally increases during intense physical activity and high heat. As long as the child has easy access to water and feels thirsty, these losses can be compensated. There is also fever, which can lead to excessive sweating. In this context, the sensation of thirst may no longer be sufficient and may seem secondary compared to other symptoms. It is then necessary to encourage regular hydration, even in small quantities.

Finally, the simplest cause of dehydration is insufficient water consumption. This can be due to a child underestimating their thirst, or not having a drink available. It is therefore important to regularly offer them water, even in the absence of complaints from them, and especially to teach them to recognize the signs of thirst or fatigue related to dehydration.

3. Types of Rehydration

There are several ways to rehydrate, which vary according to their effectiveness, ease of use, and taste acceptability.

3.1 Oral Rehydration (First-line Solution)

First, there are oral rehydration solutions (ORS). They involve ingesting a solution containing water, electrolytes (notably sodium, potassium, and chloride), and glucose. These elements facilitate the absorption of water by the intestine via sodium-glucose co-transport (SGLT-1). They are an essential solution in cases of moderate to severe dehydration, when water consumption alone is no longer sufficient, or when the necessary volumes would be too large to be well tolerated.

They are thus recommended for infants, who are more vulnerable and can be difficult to rehydrate, especially after gastroenteritis, which causes significant water and electrolyte losses. However, they can be useful at any age as soon as dehydration becomes visible, especially in aggravating circumstances such as high heat.

If you do not have a ready-to-use ORS, it is possible to prepare a simple homemade solution, recommended by the WHO:

• 1 liter of water (preferably boiled then cooled)
• 6 level teaspoons of sugar (≈ 30g)
• ½ level teaspoon of salt (≈ 2.5g)

Mix well until completely dissolved, then administer the solution in small, repeated quantities. Strictly adhere to these proportions: an excess of salt can be dangerous for the child; this solution does not replace medical advice if in doubt.

3.2 Intravenous Rehydration (Severe Cases)

In cases of moderate to severe dehydration, intravenous rehydration may be implemented in the hospital. This particularly concerns situations where oral rehydration is impossible or insufficient: inability to drink, excessively large fluid losses, or marked electrolyte imbalance.

Once a healthcare professional has determined that this method is necessary, the patient is placed on an IV drip. A solution composed of water, glucose, and electrolytes is slowly administered into the blood. The patient is then closely monitored to avoid fluid overload and to observe changes in their condition.

This method of rehydration bypasses the digestive system, which is particularly useful in cases of digestive disorders or impaired absorption. Hospital monitoring also allows for precise control of water and electrolyte levels in the blood, which cannot be done at home. However, this method is reserved for hospital settings or emergency care, with indications strictly defined by a doctor.

4. Recommended Practices for Child Hydration

Beyond ORS, other methods can effectively contribute to maintaining or restoring good hydration in children. Encouraging frequent intake of small amounts of water is more pleasant for the child but requires particular attention and regular reminders from parents.

Incorporating water-rich foods can also supplement fluid intake:

• Fresh fruits (watermelon, melon, orange, strawberries)
• Vegetables (cucumber, tomato, zucchini)
• Light broths and soups, particularly appreciated in cases of fatigue or loss of appetite

Not all drinks are equal when it comes to hydration: sodas or concentrated juices will be less effective than plain water or a slice of watermelon, due to their high sugar content. At home, a few simple habits help to establish these good practices: offering water at set times (meals, waking up, after school), varying containers to make drinking more appealing, and avoiding conditioning fluid intake on the expression of already established thirst.

5. Preventing Dehydration in Children

As the saying goes, prevention is better than cure. By establishing good hydration habits from an early age, you significantly reduce the risk of dehydration.

Make sure your child adopts good daily habits. They should always have a water bottle or a glass of water within reach, especially on hot days or during physical activities. Teach them to drink regularly, even when not feeling thirsty, such as in case of fever, or after vomiting or diarrhea, when fluid and electrolyte losses are increased. Also, make them aware of listening to their body: unusual fatigue, a dry mouth, darker urine, or headaches can be early signs of dehydration. Encourage them to tell you as soon as they feel them.

For your part, learn the first signs of dehydration to be able to react as quickly as possible.

To learn more, also consult the Ameli.fr dehydration sheet, the dedicated page on Santé.fr, or the professional sheet from the MSD Manual.

Bibliography

EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary reference values for water. EFSA Journal 2010; 8(3):1459. https://doi.org/10.2903/j.efsa.2010.1459

Sentongo T. A. (2004). The use of oral rehydration solutions in children and adults. Current gastroenterology reports, 6(4), 307-313. https://doi.org/10.1007/s11894-004-0083-5