Children are the most susceptible to dehydration because they are often unable to communicate effectively, their parents are often new to the world of parenting and although mean well may not adequately understand the signs and symptoms of dehydration, and because children (who are always keen to put things in their mouth) experience the most amount of gastroenteritis of any age bracket.
The most common cause of dehydration in children is gastroenteritis, which results in large quantities of fluid loss through vomiting and diarrhoea. Other relatively common causes of dehydration include poor oral intake due to diseases such as diabetes mellitus, which causes osmotic diuresis (and is generally diagnosed in childhood) and insensible fluid loss due to infections and fever. As a paramedic, we attend many children who appear dehydrated. Often, the dehydration can easily be corrected with an increase in oral fluid intake and correction of the fluid loss. However, it is important to look for the illness that you do not see. For example, check for early signs of diabetes mellitus (diabetes type 1).
If the child has vomiting and diarrhoea, check with the parents how they are replacing the child’s fluids. Too much clear fluids (tap water) will replace the fluid volume, but not the solvents (salt) and the child may become hyponatremic. This is where the plasma volume has been reduced, while the free fluid (water) has maintained its normal levels. Dehydration with concurrent hyponatremia is clinically more dangerous than dehydration on its own. Alternatively, too much boiled milk, thickened soups or incorrectly diluted infant formula will cause the child to become hypernatremic. In this case, the child will have adequate plasma volume without adequate free fluid replacement. Hypernatremia if left untreated will lead to CNS disturbances, seizures and eventually death. However, it is generally treated easily with basic IV fluid replacement. There is a potential risk of cerebral oedema if excessive free fluid replacement is provided too rapidly.
Dehydration versus volume depletion – The terms dehydration and volume depletion are commonly used synonymously when discussing intravascular fluid depletion. In generally, this is correct, however, as a paramedic or any other clinician, it is important to understand how the two terms may vary.
Volume depletion involves a reduction of the total intravascular plasma pool; whereas dehydration is caused by loss of plasma free water (which is disproportionate to the loss of sodium). Although both volume depletion and dehydration are caused by fluid loss, it is important to identify the differences because you can have one without the other and the medical treatment should differ accordingly.
In children with dehydration, the most common underlying problem actually is volume depletion, not dehydration. Intravascular sodium levels are within the normal range, indicating that excess free water is not being lost from plasma. Instead, the entire plasma pool is reduced along with solutes (mostly salt) and solvents (mostly water) in proportional quantities. This is volume depletion without dehydration. The most common cause is excessive extrinsic loss of fluids in conditions such as vomiting and diarrhoea which is commonly seen in just about every child at some stage in their early life.
Children are often susceptible to volume depletion as a result of vomiting, diarrhoea, or increases in insensible water loss through fevers. Significant fluid losses may occur rapidly. Children may utilise more fluid than an adult and at a much faster rate because they have: higher metabolisms, increased body surface area to mass index, and higher water content than adults. Most anatomy and physiology textbooks identify average water content in the human body at various stages of life to be 70% in infants, 65% in children, 60% in adults and less than 50% by the age of 80!
As paramedics, it is important to be particularly diligent when assessing small children with suspected dehydration. Most children will become dehydrated at some stage in their life and they will respond well to treatment. But unrecognised, the dehydrated child may continue to progress down a very steep spiral of systemic pathologies.